[71] "Hypermetamorphoses et Moeurs des Meloides," Ann. Sc. Nat., iv. Serie, t. 7, 1857, p. 299; also "Nouvelles observations sur l'hypermetamorphose et les Moeurs des Meloides," ibid., t. 9, 1858, p. 265.



Carcasses of animals stored up.—These insects lay up for their offspring stores manufactured by themselves or by others. The class we are now about to consider makes provision of animals either dead or in a torpid condition, with more or less art and more or less sure instinct. Most people have seen the Necrophorus or Burying Beetle working in fields or gardens. These are large Coleoptera who feed on abandoned carrion; everything is good to them—bodies of small mammals, birds, or frogs; they are very easy to please, and as long as the beast is dead that is all they require. When they have found such remains, and consider only how to satisfy their hunger, they do not take much trouble, and gnaw the prey on the spot where they have found it. They are not alone at the feast, and in spite of their diligence numerous rivals come up to dispute it; it is necessary to share with a great number of noisy and voracious flies and insects. In the adult state they come out well from this competition; but as good parents they wish to save their larvae from it, as in a feeble condition these might suffer severely. They desire to lay up a carcass for their young alone, and with this object they bury it in the earth. The eggs also which will thus develop in the soil have more chance of escaping destruction by various insectivorous animals. If these diggers find a rat (Fig. 16) or a dead bird, three or four unite their efforts, glide beneath it, and dig with immense activity, kicking away with their hind legs the earth withdrawn from the hole. They do not pause, and their work soon perceptibly advances. The rat gradually sinks in the pit as it grows deeper. When they have the good fortune to find the earth soft they can sink the prey in less than two hours to a depth of thirty centimetres. At this level they stop, and throw back into the hole the earth they have dug out, carefully smoothing the hillock which covers the grave. Thus stored up, the carcass is ready to receive the Necrophorus eggs. The females enter the soil and lay on the buried mammal; then they retire, satisfied to leave their little ones, when they appear, face to face with such abundant nourishment. When they emerge from the envelope the young larvae find themselves in the presence of this stored food, which has been softened by putrefaction and rendered more easy of digestion. If the treasure has not fallen on a spot easy to dig, the Necrophorus quickly recognise the fact, and do not waste time in useless labour. Endowed with considerable strength relatively to their size, three or four of them creep beneath the prey, and co-ordinating their efforts they transport it several metres off to a spot which they know by experience to be suitable for their labours. It may happen that soft earth is too far away, and transport becoming too difficult a task, they renounce it. But as good food should never be wasted, they utilise it by feeding themselves, awaiting a more manageable god-send for their offspring.

Many observers have studied these beetles, and all are surprised at their sagacity, and the way in which their various operations are adapted to circumstances; genuine reflection governs their acts, which are always combined to produce a definite effect.

Provision of paralysed living animals.—It is unnecessary to say how much better it would be for the young larva to have at its disposal instead of a carcass a living animal, but paralysed and rendered motionless by some method. It is difficult to believe the thing possible, yet nothing is better established. There is a hymenopterous relative of the Wasp called the Sphex. Instead of laying up honey they store animal provisions for their larvae. Fabre has studied one of them, the Sphex flavipennis.[72] It is in September that this wasp lays her eggs; during this month to shelter her little ones she hollows out a dozen burrows and provisions them. She has then to devote about three days' work to each of them, for there is much to do, as may be imagined. For each of these hiding-places the Sphex first pierces a horizontal gallery about two or three inches long; then she bends it obliquely so that it penetrates deeply into the earth, and it is again continued in this direction for about three inches. At the end of this passage three or four chambers are made, usually three; each of these is meant to receive one egg. The insect interrupts its mining task, not forming the three chambers consecutively; when the first is completed she provisions it—we shall soon see in what manner—and lays an egg there; then she blocks it up, suppressing all communication between this cell and the gallery; this done she bores a second passage, provisions it, and lays another egg, closes up the orifice, and proceeds to prepare the third. This work is pushed on with great activity, and when completed the Sphex entirely fills up the subterranean passage, and completely isolates the hope of the race at a depth sufficient to shelter it well. A last precaution is taken: before leaving, the rubbish in front of the obstructed opening is cleared away, and every trace of the operation disappears. The nest is then definitely abandoned, and another one prepared.

[72] "Etude sur l'instinct et les metamorphoses des Sphegiens," Ann. Sci. Nat., 1856.

The chambers in which the larvae are enclosed—hastily made with little care, and with rough unsmoothed walls—are not very solid, and could not last long without slipping; but as they only have to last for a single season they possess sufficient resistance for the insect's purpose. The larva also knows very well how to protect itself against the roughness of the walls, and overlays them with a silky secretion produced by its glands.

We have now to consider the nature of the provisions placed by the Sphex near the egg. Each cell must contain four crickets. That is the amount of food necessary for a larva during its evolution, and these insects are in fact large enough to supply a considerable amount of nourishment. When the Sphex interrupts digging operations it is to fly on a hunting expedition. It soon returns with a cricket it has seized, holding it by one antenna which it turns round in its jaws. It is a heavy burden for the slender Sphex to bear. Sometimes on foot, dragging its burden after it, sometimes flying, and carrying the suspended cricket always in a passive condition, the burrow is gradually reached, not without difficulty. In spite of appearances, the cricket is not dead; it cannot move, but if kept for several days it will not putrefy, and its joints remain supple. It is simply the victim of a general paralysis.

The cause of the paralysis.—It was evidently of the greatest interest to know how the Sphex contrived this capture, and what method it used to suppress the movements of the prey. In order to obtain the solution of this problem, Fabre during a long period accumulated experiments and observations, and at last discovered in every detail how the thing was done. In order to compel the Sphex to act in his presence, he placed himself in front of the orifice of a gallery in which the insect was working; he soon saw it returning with a paralysed cricket. Arrived at the burrow, the insect placed the prey on the ground for a moment and disappeared in the passage to see that everything was in order, and that no damage had taken place since its departure. Everything was going well, and it reappeared, took up its burden, and again entered the subterranean passage, drawing the victim along. It brought it into the chamber for which it was destined, placing it on its back, the head down and the feet towards the door. Then it set out hunting again until it had ranged four crickets side by side. Before attempting a decisive experiment, the observer felt his way. At the moment when the Sphex was buried in the earth examining the chamber, Fabre withdrew the prey a short distance and awaited events. Having made the domiciliary visit, the Sphex then went straight to the place where it had left its insect, but could not find it. It was naturally very perplexed, and examined the neighbourhood with extreme agitation, not knowing what had happened, and evidently regarding the whole affair as very extraordinary; at last it found the victim it was seeking. The cricket still preserved the same immobility; its executioner seized it by an antenna and drew it anew to the entrance of the hole. In the interior of the subterranean domain everything is in good order; the insect had just assured itself of the fact, and we should expect to see it enter with its prey; not at all, it entered alone, and only decided to introduce the prey after it had made a fresh inspection. This fact is surprising, and it is still more surprising that if the practical joke of removing the cricket is repeated several times in succession, the Sphex drags it anew every time to the entrance of the burrow and first descends alone; forty times over this experiment succeeded without the insect deciding to renounce the habitual manoeuvre. Fabre insists on this fact, and rightly, for nothing should be neglected; he makes it a text to show how automatic instinct is, and how the acts which proceed from it are invariably regulated so as to succeed one another always in the same order. In their nature these acts are quite indistinguishable from intelligent acts; only the creature is not capable of modifying them to bring them into harmony with unforeseen circumstances. All this is correct, but where it becomes excessive is in endowing animals alone with instinct and separating them from this point of view from Man. It is incontestable that the custom of visiting the burrow before introducing a victim into it has become so imperious in the Sphex that it cannot be broken, even when it is of no use. It is a mechanical instinct. But we may see an exactly parallel manifestation of human intelligence. In face of danger man utters cries of distress; they are heard and assistance comes. But these appeals are not intelligent and appropriate to the end; they are instinctive. Place the same individual in a situation where he knows very well that his voice cannot be heard; this will not hinder him from reproducing the same acts if he finds himself in the presence of danger. It is thus that the Sphex proceeds, guided by instincts, and it is no reason for despising it. And even in the course of this little experiment the insect gives proof of judgment. When it finds its cricket, it is perfectly aware that it is the same cricket which it brought, that there is no life in it, and that there is no need to re-commence the struggle; it sees too that it is not an ordinary corpse liable to putrefaction, but the very same cricket, and it does not hesitate to utilise it at once.

These habits being ascertained, Fabre proceeded to find out how the paralysis is produced. He awaited near a burrow the Sphex's arrival, dragging a victim by an antenna, and while the insect was occupied in the subterranean survey he substituted a living cricket for that which the Sphex had left, expecting to find it on the spot where it had been placed. On emerging it perceives the cricket scampering away; not a moment was to be lost, and without reflection it leapt on the refractory victim. A lively struggle followed, a duel to the death among the blades of grass; it was a truly dramatic spectacle, the agile assailant whirling around the Cricket, who kicked violently with his hind legs. If a blow were to reach the Sphex it would be disembowelled; but it avoids the blows skilfully without ceasing its own violent attack. At last the combat ends; the cricket is brought to earth, turned on to its back, and maintained in this position by the Sphex. Still on its guard, the latter seizes in its jaws one of the filaments which terminate the abdomen of the vanquished, placing its legs on the belly; with the two posterior legs it holds the head turned back so as to stretch the under side of the neck. The cricket is unable to move and the conqueror's sting wanders over the horny carapace seeking a joint, feeling for a soft place in which it can enter to give the finishing stroke. The dart at last reaches, between the head and the neck, the spot where the hard portions articulate, leaving between them a space without covering. The joint in the armour is found. The Sphex's abdomen is agitated convulsively; the sting penetrates the skin, piercing a ganglion situated just beneath this point; the venom spreads and acts on the nervous cells, which can no longer convey messages to the muscles. That is not all; the sting wanders over the cricket's belly, this time seeking the joint between the neck and the thorax; it finds it, and is again thrust in with fury; a second ganglion of the nervous chain is thus perforated and poisoned. After these two wounds the victim is completely paralysed.

As already mentioned, several facts enable us to recognise that the Cricket is by no means dead. It is simply incapable of movement, as would happen after an injection of curare. This poison kills a superior animal, for it hinders the muscular movements of the chest and diaphragm, necessary to respiration; but if a frog, which can breathe through its skin, is thus acted on it comes to life again at the end of twenty-four or forty-eight hours if the dose has not been too strong. The cricket is in a similar condition; it neither eats nor breathes; being incapable also of movement, there is no vital expenditure; it remains in a sort of torpor, or latent life, awaiting the tragic fate that is reserved for it. When it has been deposited in the little mortuary chamber the Sphex lays an egg on its thorax. The larva will soon come out to penetrate the body of the prey by enlarging the hole left by the sting. It thus finds for its first meals a food which unites the flavour of living flesh with the immobility of death. Nothing can be more convenient. When the first body is eaten it proceeds to the second, and thus devours successively the four victims stored up by maternal foresight.

In order not to interrupt the description and interfere with the succession of the acts, I have passed without remark the experiment in which Fabre substituted a living animal for the Sphex's already paralysed captive. It seems to me, however, that in this circumstance the insect showed judgment, and knew how to act in accordance with new requirements. It was evidently the first time in insect memory in which so surprising a phenomenon had been seen as a victim at the last moment again taking the field. We cannot make instinct intervene here. If the Sphex's acts are so automatic as we are sometimes led to believe, in accordance with facts which are perfectly accurate, we ought always to observe the following succession of acts: first, hollowing of the burrow; second, the chase; third, the blows of the dart; fourth, the different manoeuvres for placing the victim in the sarcophagus. Now in the present case the insect had accomplished the first three series of actions, and had even begun the fourth; it ought next to drag the cricket into the burrow without listening to the recriminations which the latter had no business to make, since it was to be regarded as having received the two routine doses of poison. But the Sphex sees its victim come to life, understands this fact, and without seeking to fathom the cause judges that a new struggle and new blows of the sting are necessary; he understands that it is necessary to begin afresh, since the usual result has not been attained. He is then capable of reflection, and the series of acts which he accomplishes are not ordained with such inflexibility that it is impossible for him to modify them in order to conform them to varying circumstances.

The Sphex occitanica acts in the same manner as its relative in this complicated art of laying up provisions for the family. The differences are only in detail. Instead of hollowing the burrow first and then setting out on the chase to fill it, it does not devote itself to the labour of digging until a successful expedition has already assured the victim. (Fig. 17.) Instead of attacking crickets it seeks a larger orthopterous insect, the Ephippigera. The struggle is no doubt more difficult, but the result is proportionately greater, and the pursuit does not need to be so often renewed; a single captive is sufficient for its larva.[73]

[73] For some remarks on the action of the Sphex, and for Darwin's opinion on the matter, see Romanes' Mental Evolution in Animals, pp. 299-303.



The sureness of instinct.—It is not doubtful that a sure inherited instinct conducts the Sphex to prick its victim in the situation of the nervous ganglia, which will be wounded in the act. It may be said that the lesion results from the position in which the hymenopterous insect maintains its victim; for the sting is on the median line, and can only penetrate at the soft points; the two points attacked are then rigorously determined by physical circumstances. But these arguments have no bearing if we consider the method of procedure adopted by the Ammophila,[74] a hymenopterous insect related to the preceding, which paralyses caterpillars. It is free in this case to insert its sting at any portion of the body; yet it knows how to turn over and arrange the captive so that the dart shall penetrate both times at two points where ganglia will be poisoned and immobility without death be induced. It must then be agreed that there is here an instinct much too sure to be called mechanical; but these facts, which considered alone seem simply marvellous, become much less so, and lend themselves to evolutionary interpretation, when it is recognised that they are related by insensible degrees to other facts of the same order, much more intelligent and at the same time less sure.

[74] Paul Marchal, "Observations sur l'Ammophila affinis," Arch. de Zool. exp. et gener., ii. Serie, t. x., 1892.

Similar cases in which the specific instinct is less powerful and individual initiative greater.—Here is, for instance, the case of the Chlorion, where each animal possesses more considerable initiative.[75] It attacks the Cockroach. These insects are of an extremely varied size, according to age, and as they are also very agile the Chlorion is not certain of being always able to obtain victims of the same dimension. The orifice of its burrow, which it hollows in walls between the crevices of the stones, is calculated on the average size of its victims. It has also the habit of paralysing the cockroach by stinging it on the nervous chain. These preliminary operations do not impede it, but it is embarrassed when it wishes to introduce through the entrance of its gallery an insect which is too large. It pulls at first as much as it can, but seeing the failure of its efforts it does not persevere in this attempt, and comes out to survey the situation. Decidedly the victim is too large and cannot pass through. The Chlorion begins by cutting off the elytra, which maintain it rigid and prevent it from being compressed. This done, it harnesses itself anew and re-commences its efforts. But this is not sufficient, and the victim still resists. The insect returns, and again examines the situation. Now it is a leg which is placed cross-ways and opposes the introduction of the body; strong diseases need strong remedies, and our Chlorion sets itself to amputate this encumbering appendage. It triumphs at last; the cockroach yields to its efforts, and little by little penetrates the hole. As may be seen, the labour is laborious and painful, and may present itself beneath various aspects which call for a certain ingenuity on the part of the animal.

[75] Reaumur, Memoires pour servir a l'histoire des Insectes, Paris, 1742, t. vi., pp. 282-284.

Up to recent years the Cerceris was considered to act with as much certainty as the Sphex, and to obey an infallible instinct which always guided it for the best in the interests of its offspring. The insects it attacks belong to the genus Buprestis. It consumes them in considerable numbers. Its manner of action, as described by Leon Dufour,[76] much resembles that of the Sphex, and it would be superfluous to describe it. The only fact which I wish to mention, and which has been put out of doubt by the illustrious naturalist, is this: the Buprestis are paralysed, not dead; all the joints of the antennae and legs remain flexible and the intestines in good condition. He was able to dissect some which had been in a state of lethargy for at least a week or a fortnight, although, under normal conditions, these insects in summer decay rapidly, and after forty-eight hours cannot be used for anatomical purposes. Another observer, Paul Marchal, took up this question afresh, and the results which he obtained seemed to indicate an instinct much less firm than earlier studies tended to show.[77]

[76] "Histoire des Cerceris," Ann. Sc. Nat., ii. Serie, t. xv., 1841, pp. 353-370.

[77] Arch. de Zool. exp., 1887.

Genera less skilful in the art of paralysing victims.—These researches show us that in the Cerceris instinct is still subject to defect. In some neighbouring genera we can seize it, as it were, in process of formation. The way in which the Bembex, or Sand Wasp, provisions burrows by maternal foresight is much less mechanical than that of the Sphex. It is again Fabre who has described with most care the customs of this hymenopterous insect.[78] It hollows out for each egg a chamber communicating with the air by a gallery, and performs this work with little care and very roughly. Less skilful than the others, it does not amass at once all the provisions which its larvae will need during the period of evolution. When the offspring has absorbed the last prey brought, it is necessary to bring a new victim. This insect is scarcely more advanced than birds, who feed their young from day to day. And it is a great labour to re-open every time the gallery which leads to the nursery; on all these visits, in fact, the Bembex fills it up on leaving, and causes the disappearance of all revealing traces. It is obliged to take so much trouble, because it has not inherited from its ancestors the receipt for the paralysing sting; it throws itself without care on its victim, delivers a few chance blows, and kills it. Necessarily it cannot, under these conditions, lay up provisions for the future; they would corrupt, and the larvae would not be benefited; hence the obligation of frequently returning to the nest, and of a perpetual hunt to feed descendants whom nature has gifted with an excellent appetite. According to the age of the offspring, the mother chooses prey of different sizes; at first she brings small Diptera; then, when it has grown, she captures for it large blow-flies, and lastly gadflies.[79] It will be seen, then, that if we suppose the instinct of the Sphex to be slowly developed by being derived from a sting given at random, we make a supposition which is quite admissible and rests on ascertained facts. However this may be, the Bembex, returning to its burrow, is able to find it again with marvellous certainty, in spite of the care taken to hide it by removing every trace that might reveal its existence. It is guided by an extraordinary topographic instinct, which men not only do not possess, but cannot even understand the nature of.

[78] Souvenirs entomologiques, 1879, pp. 225 et seq.

[79] A Wasp found in La Plata, the Monedula punctata, as described by Hudson (Naturalist in La Plata, pp. 162-164), is an adroit fly-catcher, and thus supplies her grub with fresh food, carefully covering the mouth of the hole with loose earth after each visit; as many as six or seven freshly-killed insects may be found for the use of one grub.

It would appear that certain Hymenoptera, fearing to kill their victim with the sting, and not knowing the art of skilful lesions, attempt to immobilise them by wounds of another sort. This is the case with the Pompilius, according to Goureau,[80] who has studied it. This insect nourishes its larvae with spiders; it seems certain that in most cases the spider is not pricked. Victims who have been taken from the interior of provision burrows can live for a long time in spite of their wounds; they cannot, therefore, have received venom by inoculation. The author already quoted believes that the Pompilius seizes its captive by the pedicle which unites the abdomen to the cephalothorax, and that it triturates this point between its jaws. From this either death or temporary immobility may follow. The Pompilius also makes up for its relative ignorance by considerable ingenuity. Thus sometimes, when it fears a return to life of the victim destined for its larvae, it cuts off the legs while it is still passive. Goureau has found in the nest of this insect living spiders with their legs cut off.

[80] "Observations pour servir a l'histoire de quelques Insectes," Ann. Soc. entomol. de France, t. 8, 1839, p. 541.



CHAPTER VI.

DWELLINGS.

ANIMALS NATURALLY PROVIDED WITH DWELLINGS—ANIMALS WHO INCREASE THEIR NATURAL PROTECTION BY THE ADDITION OF FOREIGN BODIES—ANIMALS WHO ESTABLISH THEIR HOME IN THE NATURAL OR ARTIFICIAL DWELLINGS OF OTHERS—CLASSIFICATION OF ARTIFICIAL SHELTERS—HOLLOWED DWELLINGS—RUDIMENTARY BURROWS—CAREFULLY-DISPOSED BURROWS—BURROWS WITH BARNS ADJOINED—DWELLINGS HOLLOWED OUT IN WOOD—WOVEN DWELLINGS—RUDIMENTS OF THIS INDUSTRY—DWELLINGS FORMED OF COARSELY-ENTANGLED MATERIALS—DWELLINGS WOVEN OF FLEXIBLE SUBSTANCES—DWELLINGS WOVEN WITH GREATER ART—THE ART OF SEWING AMONG BIRDS—MODIFICATIONS OF DWELLINGS ACCORDING TO SEASON AND CLIMATE—BUILT DWELLINGS—PAPER NESTS—GELATINE NESTS—CONSTRUCTIONS BUILT OF EARTH—SOLITARY MASONS—MASONS WORKING IN ASSOCIATION—INDIVIDUAL SKILL AND REFLECTION—DWELLINGS BUILT OF HARD MATERIALS UNITED BY MORTAR—THE DAMS OF BEAVERS.

Animals construct dwellings either to protect themselves from the cold, heat, rain, and other chances of the weather, or to retire to at moments when the search for food does not compel them to be outside and exposed to the attacks of enemies. Some inhabit these refuges permanently; others only remain there during the winter; others, again, who live during the rest of the year in the open air set up dwellings to bring forth their young, or to lay their eggs and rear the offspring. Whatever the object may be for which these retreats are built, they constitute altogether various manifestations of the same industry, and I will class them, not according to the uses which they are to serve, but according to the amount of art displayed by the architect.

In this series, as in those which we have already studied, we shall find every stage from that of beings provided for by nature, and endowed with a special organ which secretes for them a shelter, up to those who are constrained by necessity to seek in their own intelligence an expedient to repair the forgetfulness of nature. These productions, so different in their origin, can only be compared from the point of view of the part they play; there are analogies between them but not the least homology.

Animals naturally provided with dwellings.—Nearly all the Mollusca are enveloped by a very hard calcareous case, secreted by their mantle: this shell, which is a movable house, they bear about with them and retire into at the slightest warning.

Caterpillars which are about to be transformed into chrysalides weave a cocoon, a very close dwelling in which they can go through their metamorphosis far from exterior troubles. It is an organic form of dwelling, or produced by an organ. It is not necessary to multiply examples of this kind; they are extremely numerous. In the same category must be ranged the cells issuing from the wax-glands which supply Bees with materials for their combs in which they enclose the eggs of the queen with a provision of honey.

I do not wish to insist on creations of this kind which are independent of the animal's will and reflection. Near these facts must be placed those in which animals, still using a natural secretion, yet endeavour to obtain ingenious advantages from it unknown by related species.



There is, for example, the Macropus viridi-auratus, or Paradise-fish, which blows air bubbles in the mucus produced from its mouth. This mucus becomes fairly resistant, and all the bubbles imprisoned and sticking aside by side at last form a floor. It is beneath this floating shelter that the fish suspends its eggs for its little ones to undergo their early development.

Animals who increase their natural protection by the addition of foreign bodies.—Certain tubicolar Annelids, whose skin furnishes abundant mucus which does not become sufficiently hard to form an efficacious protection, utilise it to weld together and unite around them neighbouring substances, grains of sand, fragments of shell, etc. They thus construct a case which both resembles formations by special organs and manufacture by the aid of foreign materials. The larvae of Phryganea, who lead an aquatic life, use this method to separate themselves from the world and prepare tubes in which to dwell. (Fig. 18.) All the fragments carried down by the stream are good for their labours on condition only that they are denser than the water. They take possession of fragments of aquatic leaves, and little fragments of wood which have been sufficiently long in the water to have thoroughly imbibed it and so become heavy enough to keep themselves at the bottom, or at least to prevent them from floating to the surface. It is the larva of Phryganea striata which has been best studied; those of neighbouring species evidently act much in the same way, with differences only in detail. The little carpenter stops a fragment rather longer than his own body, lies on it and brings it in contact with other pieces along his own sides. He thus obtains the skeleton of a cylinder. The largest holes are filled up with detritus of all kinds. Then these materials are agglutinated by a special secretion. The larva overlays the interior of its tube with a covering of soft silk which renders the cylinder watertight and consolidates the earlier labours. The insect is thus in possession of a safe retreat. Resembling some piece of rubbish, it completes its metamorphosis in peace, undisturbed by the carnivora of the stream. There is here already a tendency towards the dwellings of which I shall speak later on, and which are entirely formed of the external environment.

Animals who establish their home in the natural or artificial dwellings of others.—Between the beings whom nature has endowed with a shelter and those who construct it by their own industry, we may intercept those who, deprived of a natural asylum and not having the inclination or the power to make one, utilise the dwellings of others, either when the latter still inhabit them, or when they are empty on account of the death or departure of the owner. In the natural sciences there is no group of facts around which may be traced a clear boundary; each of them is more or less closely related to a group which appears at first of an entirely different nature. Thus it does not enter into our plan to speak of parasites. Yet, if among these some turn to a host to demand of him both food and shelter, if even they can come to be so modified and so marked by parasitism that they can live in no other way, there are others who ask for lodging only from an animal better protected than they are themselves. It is these whose customs we are called upon to consider. In the interior of the branchial chamber of many bivalvular Mollusca, and especially the Mussel, there lives a little crustaceous commensal called the Pea-crab (Pinnoteres pisum). He goes, comes, hunts, and retires at the least alarm within his host's shell. The mussel, as the price of its hospitality, no doubt profits by the prizes which fall to the little crab's claws. It is even said that the crab in recognition of the benefits bestowed by his indolent friend keeps him acquainted with what is passing on around, and as he is much more active and alert than his companion he sees danger much farther away, and gives notice of it, asking for the door to be shut by lightly pinching the mussel's gill. But this gratitude of the Crustacean towards a sympathetic bivalve is merely a hypothesis; we do not exactly know what passes in the intimacy of these two widely-differing natures.

For birds like the Cuckoo and the Molothrus it is not possible to plead attenuating circumstances. They occupy a place in an inhabited house without paying any sort of rent. Every one knows the Cuckoo's audacity. The female lays her eggs in different nests and troubles herself no further about their fate. She seeks for her offspring a shelter which she does not take the trouble to construct, and moreover at the same time assures for them the cares of a stranger in place of her own.

In North America a kind of Starling, the Molothrus pecoris, commonly called the Cow-bird, acts in the same careless fashion. It lives in the midst of herds, and owes its specific name to this custom; it feeds on the parasites on the skin of cattle. This bird constructs no nest. At the moment of laying the female seeks out an inhabited dwelling, and when the owner is absent she furtively lays an egg there. The young intruder breaks his shell after four days' incubation, that is to say, usually much before the legitimate children; and the parents, in order to silence the beak of the stranger who, without shame, claims his share with loud cries, neglect their own brood which have not yet appeared, and which they abandon. Their foster children repay them, however, with the blackest ingratitude. As soon as the little Molothrus feels his body covered with feathers and his little wings strong enough to sustain him he quits his adopted parents without consideration. These birds show a love of independence very rare among animals, with whom conjugal fidelity has become proverbial; they do not unite in couples; unions are free, and the mother hastens to deliver herself from the cares of bringing up her young in the manner we have seen. Two other species of Molothrus have the same habit, as have the American Cuckoo and the Golden Cuckoo of South Africa.

The habits of the Molothrus bovariensis, a closely allied Argentine Cow-bird, have been carefully studied by Mr. W. H. Hudson, who has also some interesting remarks as to the vestiges of the nesting instinct in this interesting parasitical bird, which now is constantly dropping eggs in all sorts of places, even on the ground, most of them being lost. "Before and during the breeding-season the females, sometimes accompanied by the males, are seen continually haunting and examining the domed nests of the Dendrocolaptidae. This does not seem like a mere freak of curiosity, but their persistence in their investigations is precisely like that of birds that habitually make choice of such breeding-places. It is surprising that they never do actually lay in such nests, except when the side or dome has been accidentally broken enough to admit the light into the interior. Whenever I set boxes up in my trees, the female Cow-birds were the first to visit them. Sometimes one will spend half a day loitering about and inspecting a box, repeatedly climbing round and over it, and always ending at the entrance, into which she peers curiously, and when about to enter starting back, as if scared at the obscurity within. But after retiring a little space she will return again and again, as if fascinated by the comfort and security of such an abode. It is amusing to see how pertinaciously they hang about the ovens of the Oven-birds, apparently determined to take possession of them, flying back after a hundred repulses, and yet not entering them even when they have the opportunity. Sometimes one is seen following a Wren or a Swallow to its nest beneath the eaves, and then clinging to the wall beneath the hole into which it disappeared. That it is a recurrence to a long-disused habit I can scarcely doubt. I may mention that twice I have seen birds of this species attempting to build nests, and that on both occasions they failed to complete the work. So universal is the nest-making instinct that one might safely say the M. bovariensis had once possessed it, and that in the cases I have mentioned it was a recurrence, too weak to be efficient, to the ancestral habit." Mr. Hudson suggests that this bird lost the nest-making instinct by acquiring the semi-parasitical habit, common to many South American birds, of breeding in the large covered nests of the Dendrocolaptidae, although, owing to increased severity in the struggle for the possession of such nests, this habit was defeated.[81]

[81] P. L. Sclater and W. H. Hudson, Argentine Ornithology, 1888, vol. i. pp. 72-86. A brief summary of the facts regarding parasitism among birds will be found in Girod's Les Societes chez les Animaux, 1891, pp. 287-294.

The Rhodius anarus, a fish of European rivers, also ensures a quiet retreat for his offspring by a method which is not less indiscreet. At the period of spawning, a male chooses a female companion and with great vigilance keeps off all those who wish to approach her. When the laying becomes imminent, the Rhodius, swimming up and down at the bottom of the stream, at length discovers a Unio. The bivalve is asleep with his shell ajar, not suspecting the plot which is being formed against him. It is a question of nothing less than of transforming him into furnished lodgings. The female fish bears underneath her tail a prolongation of the oviduct; she introduces it delicately between the Mollusc's valves and allows an egg to fall between his branchial folds. In his turn the male approaches, shakes himself over it, and fertilises it. Then the couple depart in search of another Unio, to whom to confide another representative of the race. The egg, well sheltered against dangers from without, undergoes development, and one fine day the little fish emerges and frisks away from his peaceful retreat.

Other animals, more respectful of property, avoid using another's dwelling until it is abandoned by its proprietor, and no reproach of indelicacy can be addressed to the Gobius minutus, a fish which lives on our coasts at the mouth of rivers. The female lays beneath overturned shells, remains of Oysters, or Cardium shells. The valve is buried beneath several centimetres of sand, which supports it like a vault. It forms a solid roof, beneath which the eggs undergo their evolution. Sometimes the male remains by the little chamber to watch over their fate. It is possible to distinguish the two holes of entrance and exit which mark his habitual passage.



The Hermit-crab perhaps knows best how to take advantage of old clothes. (Fig. 19.) He collects shells of Gasteropods, abandoned flotsam, the first inhabitant of which has died. The Hermit-crab (Pagurus Bernhardus) is a Decapod Crustacean—that is to say, he resembles a very small Crab. But his inveterate habit during so many generations of sheltering his abdomen in a shell prevents this part from being encrusted with lime and becoming hard. The legs and the head remain in the ordinary condition outside the house, and the animal moves bearing it everywhere with him; on the least warning he retires into it entirely. But the Crustacean grows. When young he had chosen a small shell. A Mollusc, in growing, makes his house grow with him. The Hermit-crab cannot do this, and when his dwelling has become too narrow he abandons it for one that is more comfortable. At first enclosed in the remains of a Trochus, he changes into that of a Purpura; a little later he seeks asylum in a Whelk. Beside the shelter which these shells assure to the Crustacean, they serve to mask his ferocity, and the prey which approaches confidently what it takes to be an inoffensive Mollusc, becomes his victim.

The Great Horned Owl likewise does not construct a nest; but takes possession of the dwellings abandoned by others. These birds utilise for laying their eggs sometimes the nest of a Crow or a Dove, sometimes the lair which a Squirrel had considered too dilapidated. The female, without troubling about the bad state of these ruins, or taking pains to repair them, lays her eggs here and sits on them.

Classification of artificial shelters.—It is time to turn to animals who have more regard for comfort, and who erect dwellings for themselves or their offspring. These dwellings may be divided into three groups: (1) Those which are hollowed in earth or in wood; (2) those which in the simplest form result from the division of material of any kind; then, as a complication, of materials bound together; then, as a last refinement, of delicate materials, such as blades of grass or threads of wool woven together; such are the nests of certain birds and the tents of nomads; (3) those which are built of moist earth which becomes hard on drying; the perfection of this method consists of piling up hard fragments, pieces of wood or ashlar, the moist earth being only a mortar which unites the hard parts together. Animals exercise with varying success these different methods, all of which Man still practises.

Hollowed dwellings—Rudimentary burrows.—We will first occupy ourselves with the dwelling hollowed in the earth. It is the least complicated form. The number of creatures who purely and simply bury themselves thus to obtain shelter is incalculable; I will only mention a few examples, and pass on from simple combinations to the more perfected industries, of which they present the first sketch.

It is known that at a certain epoch of the year Crabs abandon their hard carapaces. This phenomenon is known by the name of the moult; they remain in this condition for some time; it is the period during which they grow; then their integuments are encrusted anew with lime and again become resistant. While they are thus deprived of their ordinary protection they are exposed to a crowd of dangers, and they are so well aware of this that they remain hidden beneath rocks and pebbles. A crab of Guadeloupe, called Gecarinus ruricola, escapes the perils of this situation, thanks to its kind of life and its habit of hollowing out a burrow to live in while it is deprived of its habitual defence. This Crustacean lives on the earth, at a distance of about ten or twelve kilometres from the sea-shore, and nourishes itself on animal and vegetable remains. It approaches the water only at the period of laying eggs, turning towards the coast in the months of February and March. This migration does not take place, like some others, in compact bands; each follows the road in independence, and preserves a certain amount of liberty with regard to the path and the epoch of the journey. They lead an aquatic life till May or June; then the female abandons her little ones, who had begun their development attached to her claws, and they return to land. The moult takes place in August. At the approach of this dreaded crisis each hollows a hole between two roots, supplies it with green leaves, and carefully stops up the entrance. These labours accomplished, the crab is entirely sheltered; it undergoes the moult in safety, and does not emerge from its retreat until it is again capable of facing enemies, and of seizing food with its claws, which have become hard again. This seclusion appears to last a month. Here is, then, an example of a temporary dwelling rendered necessary by special conditions of defect for external life. We are here still in the infancy of the art.

Speaking generally, birds are accomplished architects. Certain of them are, however, content with a rudimentary cavern. There is no question here of those who retire to clefts in the rock or in trunks of trees, for in these cases the cavity is only the support of the true house, and it is in the construction of this that the artist reveals his talent. I wish to speak of animals which remain in a burrow without making a nest there. A Parroquet of New Zealand called the Kakapo (Strigops habroptilus) thus dwells in natural or hollowed excavations. It is only found in a restricted portion of the island and leads a miserable life there, habitually staying in the earth and pursued by numerous enemies, especially half-wild dogs. It tries to hold its own, but its wings and beak do not suffice to protect it, and the race would have completely disappeared if these birds were not able to resist, owing to the prudence with which they stay within their dwellings. They profit by a natural retreat, or one constructed in rocks or beneath roots of trees; they only come out when impelled by hunger, and return as soon as they can in case of danger.

A large number of animals also hollow out shelters for their eggs, with the double object of maintaining them at a constant temperature and of concealing them. Most reptiles act in this manner. The way in which a Tortoise, the Cistudo lunaria, prepares its nest is extremely curious. When the time for this labour arrives, the tortoise chooses a site. It commences by boring in the earth with the end of its tail, the muscles of which are held firmly contracted; it turns the tail like a gimlet and succeeds in making a conical hole. Gradually the depth of the hole becomes equal to the length of the tail, and the tool then becomes useless. The Cistudo enlarges the cavity with the help of its posterior legs. Using them alternately it withdraws the earth and kicks it away, then piles up this rubbish on the edge of the hole, arranging it so as to form a circular rampart. Soon the posterior members can take nothing more from the too distant bottom. The moment for laying has now come. As soon as the egg arrives at the cloaca one of the feet seizes it and lowers it gently into the nest, while the second foot seizes another egg, which during this time had appeared at the orifice. This manipulation lasts until the end of the operation, when the tortoise buries all its family, and to flatten the prominence which results she strikes it repeatedly with her plastron, raising herself on her legs.

It is not only land animals which adopt this custom of living in the earth, and there sheltering their offspring. Fish also make retreats on the bank or at the bottom. To mention only one case, the Bullhead (Cottus gobio) of our rivers, which spawns in the Seine in May, June, and July, acts in this manner. Beneath a rock in the sand it prepares a cavity; then seeks females and brings them to lay eggs in its little lodging. During the four or five weeks before they come out it watches the eggs, keeping away as far as possible every danger which threatens them. It only leaves its position when pressed by hunger, and as soon as the hunt is concluded, returns to the post of duty.

Other animals when digging have a double object; they wish to shelter themselves, and at the same time to find the water which they need for themselves or for the development of their young.

It is well known that Frogs and Toads generally go in the spring to lay their eggs in streams and ponds. A Batrachian of Brazil and the hot regions of South America, the Cystignathus ocellatus, no doubt fearing too many dangers for the spawn if deposited in the open water, employs the artifice of hollowing, not far from the bank, a hole the bottom of which is filled by infiltration. It there places its eggs, and the little ones on their birth can lead an aquatic life while being guaranteed against its risks.

A terrestrial Crab, the Cardisoma carnifex, found in Bengal and the Antilles, acts in the same manner; but in this case it has in view its own convenience and not care for its offspring. Its habitat is especially in low-lying spots near the shore, where water may be found at a trifling depth beneath the soil. To establish its dwelling, the Crustacean first buries itself until it reaches the liquid level. Arrived at this point, it makes a large lair in the soft soil, and effects communication with the outside by various openings. It can thus easily come and go and retire into its cave, where it finds security and a humidity favourable for branchial respiration. From time to time it cleans out the dirt and rubbish which accumulate in the hole. It makes a little pile of all the refuse which it finds, and, seizing it between its claws and abdomen, carries it outside. Executing several journeys very rapidly, it soon clears out its dwelling.

The dipnoid Protopterus, which inhabits the marshes of Senegal and Gambia, is curious in more than one respect. Firstly, it can breathe oxygen, whether, like other fish, it finds it dissolved in water or in the atmospheric air. When during the summer the marshes in which it lives dry up, it takes refuge in the mud at the bottom, which hardens and imprisons it, and it thus remains curled up until the time when the water after the rainy season has softened the earth which surrounds it. This fact had been known for some time; travellers had brought back lumps of dried earth of varied size, the largest about as big as two fists. On opening them the same fish was always found within, and the chamber in which it is contained was lined with a sort of cocoon, having the appearance of dry gelatine. Dumeril was able to observe one of these animals in captivity. At the period corresponding to the dry period of its own country, the Protopterus buried itself in the mud which had been placed at the bottom of the aquarium. In order to realise the conditions found in nature, the water which covered it was gradually withdrawn. The earth hardened in drying, and when broken the recluse was seen surrounded by hardened mucus, exactly like those which came from Senegal.

Carefully-disposed burrows.—All the cases which we have considered show us the industry of the hollowed dwelling in its primitive state; but other animals know how to furnish it with greater luxury. I will continue in the same order of increasing complication. Many beings live permanently in a burrow; Reptiles—Snakes or Lizards—are to be placed among these. Among others, the Lacerta stirpium arranges a narrow and deep hole, well hidden beneath a thicket, and retires into it for the winter, when cold renders it incapable of movement and at the mercy of its enemies. Before giving itself up to its hybernal sleep, it is careful to close hermetically the opening of the dwelling with a little earth and dried leaves. When spring returns and the heat awakens the reptile, it comes out to warm itself and to hunt, but never abandons its dwelling, always retiring into it in case of alarm and to pass there cold days and nights.

Darwin has observed and described[82] how a little Lacertilian, the Conolophus subcristatus, conducts its work of mining and digging. It establishes its burrow in a soft tufa, and directs it almost horizontally, hollowing it out in such a way that the axis of the hole makes a very small angle with the soil. This reptile does not foolishly expend its strength in this troublesome labour. It only works with one side of its body at a time, allowing the other side to rest. For instance, the right anterior leg sets to work digging, while the posterior leg on the same side throws out the earth. When fatigued, the left legs come into play, allowing the others to repose.

[82] Voyage of the Beagle.

Other animals, without building their cavern with remarkable skill, show much sagacity in the choice of a site calculated to obtain certain determined advantages. In Egypt there are dogs which have become wild. Having shaken off the yoke of man, which in the East affords them little or no support, they lead an independent life. During the day they remain quiescent in desert spots or ruins, and at night they prowl about like jackals, hunting living prey or feeding on abandoned carcasses. There are hills which have in a manner become the property of these animals. They have founded villages there, and allow no one to approach. These hills have an orientation from north to south, so that one slope is exposed to the sun from morning to mid-day and the other from mid-day to evening. Now, dogs have a great horror of heat. They fear the torrid heat of the south as much as in our climate they like to lie warmed by gentle rays; there is no shadow too deep for their siesta. Therefore, on these Egyptian hills every dog hollows out a lair on both slopes. One of these dwellings is thus turned towards the east, the other towards the west. In the morning, when he returns from his nocturnal expeditions, the animal takes refuge in the second, and remains there until mid-day, sunk in refreshing sleep. At that hour the sun begins to reach him, and to escape it he passes over to the opposite slope; it is a curious sight to see them all, with pendent heads and sleepy air, advance with trailing steps to their eastern retreat, settle down in it, and continue their dream and their digestion till evening, when they again set forth to prowl. We never grow tired of admiring the intelligence of their domesticated fellows, but this trait seems to me worthy of remark; it proves a very developed power of observation and reflection.



The Trap-door Spiders of the south of Europe construct burrows which have been studied with great care and in much detail by Moggridge.[83] He found that there were four chief types of burrow, shown in the accompanying illustration (Fig. 20) at about one-third the actual size (except C1 and D1, which are of natural size). While A and B have only one door, C and D, besides the surface door, have another a short way under ground. The whole burrow as well as the door are lined with silk, which also forms the hinge. The great art of the Trap-door Spider lies in her skilful forming of the door, which fits tightly, although it opens widely when she emerges, and which she frequently holds down when an intruder strives to enter, and in the manner with which the presence of the door is concealed, so as to harmonise with surrounding objects. Perhaps in no case is the concealment more complete than when dead leaves are employed to cover the door. In some cases a single withered olive leaf is selected, and it serves to cover the entrance; in other cases several are woven together with bits of wood or roots, as in the accompanying illustration, which represents such a door when open and when shut. (Fig. 21.)

[83] J. T. Moggridge, Harvesting Ants and Trap-door Spiders, contained in two elaborately illustrated volumes, London, 1873-74.

The Trap-door Spider (Mygale henzii, Girard), which is widely diffused in California, forms a simple shaft-like burrow, but, like the European Trap-door Spider, it is very skilful in forming an entrance and in concealing its presence. Its habits have lately been described by D. Cleveland of San Diego.[84] In the adobe land hillocks are numerous; they are about a foot in height, and some three or four feet in diameter. These hillocks are selected by the spiders—apparently because they afford excellent drainage, and cannot be washed away by the winter rains—and their stony summits are often full of spiders' nests. These subterranean dwellings are shafts sunk vertically in the earth, except where some stony obstruction compels the miner to deflect from a downward course. The shafts are from five to twelve inches in depth, and from one-half to one and a half inches in diameter, depending largely upon the age and size of the spider.

[84] Science, 20th January 1893.

When the spider has decided upon a location, which is always in clay, adobe or stiff soil, he excavates the shaft by means of the sharp horns at the end of his mandibles, which are his pick and shovel and mining tools. The earth is held between the mandibles and carried to the surface. When the shaft is of the required size, the spider smoothes and glazes the wall with a fluid which is secreted by itself. Then the whole shaft is covered with a silken paper lining, spun from the animal's spinnerets.

The door at the top of the shaft is made of several alternate layers of silk and earth, and is supplied with an elastic and ingenious hinge, and fits closely in a groove around the rim of the tube. This door simulates the surface on which it lies, and is distinguishable from it only by a careful scrutiny. The clever spider even glues earth and bits of small plants on the upper side of his trap-door, thus making it closely resemble the surrounding surface.

The spider generally stations itself at the bottom of the tube. When, by tapping on the door, or by other means, a gentle vibration is caused, the spider runs to the top of his nest, raises the lid, looks out and reconnoitres. If a small creature is seen, it is seized and devoured. If the invader is more formidable, the door is quickly closed, seized and held down by the spider, so that much force is required to lever it open. Then, with the intruder looking down upon him, the spider drops to the bottom of his shaft.

It has been found by many experiments that when the door of his nest is removed, the spider can renew it five times—never more than that. Within these limitations, the door torn off in the evening was found replaced by a new one in the morning. Each successive renewal showed, however, a greater proportion of earth, and a smaller proportion of silk, until finally the fifth door had barely enough silk to hold the earth together. The sixth attempt, if made, was a failure, because the spinnerets had exhausted their supply of the web fluid. When the poor persecuted spider finds his domicile thus open and defenceless, he is compelled to leave it, and wait until his stock of web fluid is renewed.[85]

[85] The Trap-door Spiders of various parts of the world have been carefully studied, and the gradual development of their skill traced through various species, by Eugene Simon; see, for example, Actes de la Soc. Lin. de Bordeaux, 1888.

Skilful diggers prepare burrows with several entrances; some even arrange several rooms, each for a special object. The Otter seeks its food in the water, and actively hunts fish in ponds and rivers. But when fishing is over, it likes to keep dry and at the same time sheltered from terrestrial enemies. Its dwelling must also present an easy opening into the water. In order to fulfil all these conditions, its house consists first of a large room hollowed in the bank at a level sufficiently high to be beyond reach of floods. From the bottom of this keep a passage starts which sinks and opens about fifty centimetres beneath the surface of the water. It is through here that the Otter noiselessly glides to find himself in the midst of his hunting domain without having been seen or been obliged to make a noisy plunge which would put the game to flight. If this were all, the hermetically-closed dwelling would soon become uninhabitable, as there would be no provision for renewing the air, so the Otter proceeds to form a second passage from the ceiling of the room to the ground, thus forming a ventilation tube. In order that this may not prove a cause of danger, it is always made to open up in the midst of brushwood or in a tuft of rushes and reeds.

Marmots also are not afraid of the work which will assure them a warm and safe refuge in the regions they inhabit, where the climate is rough. In summer they ascend the Alps to a height of 2,500 to 3,000 metres and rapidly hollow a burrow like that for winter time, which I am about to describe, but smaller and less comfortable. They retire into it during bad weather or to pass the night. When the snow chases them away and causes them to descend to a lower zone, they think about constructing a genuine house in which to shut themselves during the winter and to sleep. Twelve or fifteen of these little animals unite their efforts to make first a horizontal passage, which may reach the length of three or four metres. They enlarge the extremity of it into a vaulted and circular room more than two metres in diameter. They make there a good pile of very dry hay on which they all install themselves, after having carefully protected themselves against the external cold by closing up the passage with stones and calking the interstices with grass and moss.

In solitary woods or roads the Badger (Meles), who does not like noise, prepares for himself a peaceful retreat, clean and well ventilated, composed of a vast chamber situated about a metre and a half beneath the surface. He spares no pains over it, and makes it communicate with the external world by seven or eight very long passages, so that the points where they open are about thirty paces distant from one another. In this way, if an enemy discovers one of them and introduces himself into the Badger's home, the Badger can still take flight through one of the other passages. In ordinary times they serve for the aeration of the central room. The animal attaches considerable importance to this. He is also very clean in his habits, and every day may be seen coming out for little walks, having an object of an opposite nature to the search for food. This praiseworthy habit is, as we shall see, exploited by the Fox in an unworthy manner.

The Fox has many misdeeds on his conscience, but his conduct towards the Badger is peculiarly indelicate. The Fox is a skilful digger, and when he cannot avoid it, he can hollow out a house with several rooms. The dwelling has numerous openings, both as a measure of prudence and of hygiene, for this arrangement enables the air to be renewed. He prepares several chambers side by side; one of which he uses for observation and to take his siesta in; a second as a sort of larder in which he piles up what he cannot devour at once; a third, in which the female brings forth and rears her young. But he does not hesitate to avoid this labour when possible. If he finds a rabbit warren he tries first to eat the inhabitants, and then, his mind cleared from this anxiety, arranges their domicile to his own taste, and comfortably installs himself in it. In South America, again, the Argentine Fox frequently takes up permanent residence in a vizcachera, ejecting the rightful owners; he is so quiet and unassuming in his manners that the vizcachas become indifferent to his presence, but in spring the female fox will seize on the young vizcachas to feed her own young, and if she has eight or nine, the young of the whole village of vizcachas may be exterminated.

The Badger's dwelling appears to the Fox particularly enviable. In order to dislodge the proprietor he adopts the following plan. Knowing that the latter can tolerate no ordure near his home, he chooses as a place of retirement one of the passages which lead to the chamber of the peaceful recluse. He insists repeatedly, until at last the Badger, insulted by this grossness, and suffocated by the odour, decides to move elsewhere and hollow a fresh palace. The Fox is only waiting for this, and installs himself without ceremony.

The Vizcacha (Lagostomus trichodactylus) is a large Rodent inhabiting a vast extent of country in the pampas of La Plata, Patagonia, etc. Unlike most other burrowing species, the Vizcacha prefers to work on open level spots. On the great grassy plains it is even able to make its own conditions, like the Beaver, and is in this respect, and in its highly-developed social instinct, among the two or three Mammals which approach Man, although only a Rodent, and even in this order, according to Waterhouse, coming very low down by reason of its marsupial affinities.

The Vizcacha lives in small communities of from twenty to thirty members, in a village of deep-chambered burrows, some twelve or fifteen in number, with large pit-like entrances closely grouped together, and as the Vizcachera, as this village is called, endures for an indefinitely long period, the earth which is constantly brought up forms an irregular mound thirty or forty feet in diameter, and from fifteen to thirty inches above the level of the road; this mound serves to protect the dwelling from floods on low ground. A clearing is made all round the abode and all rubbish thrown on the mound; the Vizcachas thus have a smooth turf on which to disport themselves, and are freed from the danger of lurking enemies.

The entire village occupies an area of one hundred to two hundred square feet of ground. The burrows vary greatly in extent; usually in a Vizcachera there are several that, at a distance of from four to six feet from the entrance, open into large circular chambers. From these chambers other burrows diverge in all directions, some running horizontally, others obliquely downwards to a maximum depth of six feet from the surface; some of these galleries communicate with those of other burrows.

On viewing a Vizcachera closely, the first thing that strikes the observer is the enormous size of the entrances to the central burrows in the mound; there are usually several smaller outside burrows. The entrance to some of the principal burrows is sometimes four to six feet across the mouth, and sometimes it is deep enough for a tall man to stand in up to the waist.

It is not easy to tell what induces a Vizcacha to found a new community, for they increase very slowly, and are very fond of each other's society. It is invariably one individual alone who founds the new village. If it were for the sake of better pasture he would remove to a considerable distance, but he merely goes from forty to sixty yards off to begin operations. Sooner or later, perhaps after many months, other individuals join the solitary Vizcacha, and they become the parents of innumerable generations in the same village: old men, who have lived all their lives in one district, remember that many of the Vizcacheras around them existed when they were children.

It is always a male who begins the new village. Although he does not always adopt the same method, he usually works very straight into the earth, digging a hole twelve or fourteen inches wide, but not so deep, at an angle of about 25 deg. with the surface. After he has progressed inwards for a few feet, the animal is no longer content merely to scatter the loose earth; he cleans it away in a straight line from the entrance, and scratches so much on this line, apparently to make the slope gentler, that he soon forms a trench a foot or more in depth, and often three or four feet in length. This facilitates the conveyance of the loose earth as far as possible from the entrance of the burrow. But after a while the animal is unwilling that earth should accumulate even at the end of this long passage, and proceeds to form two additional trenches, making an acute or right angle converging into the first trench, so that the whole when completed takes a Y shape. These trenches are continually deepened and lengthened in this manner, the angular segment of earth between them being scratched away, until by degrees it gives place to one large deep irregular mouth. The burrows are made best in the black and red moulds of the pampas; but even in such soils the entrances may be varied. In some the central trench is wanting, or so short that there appear to be but two passages converging directly into the burrow, or these two trenches may be so curved inwards as to form the segment of a circle. Usually, however, the varieties are only modifications of the Y-shaped system.

On the pampas a wide-mouthed burrow possesses a distinct advantage over the more usual shape. The two outer trenches diverge so widely from the mouth that half the earth brought out is cast behind instead of before it, thus creating a mound of equal height about the entrance, by which it is secured from water during great rainfalls, while cattle avoid treading over the great pit-like entrances, though they soon tread and break in the burrows of the Armadillo and other species when these make their homes on perfectly level ground.

The Vizcachas do not usually leave their burrows until dark, but in summer they come out before sunset. Usually one of the old males first appears, and sits on some prominent place on the mound, apparently in no haste to begin his evening meal. Other Vizcachas soon begin to appear, each quietly taking up his position at the burrow's mouth. The females, known by their smaller size and lighter colour, sit upright on their haunches, as if to command a better view; they are always wilder and sprightlier in their gestures than the males. They view a human stranger with a mixture of fear and curiosity, sometimes allowing him to come within five or six paces of them; in desert regions, however, where enemies are numerous, the Vizcacha is very timid and wary.

These animals are very sociable, and their sociability extends beyond their own vizcachera. On approaching a vizcachera at night, usually some of the Vizcachas on it scamper off to distant burrows. These are neighbours merely come to pay a friendly visit. The intercourse is so frequent that little straight paths are formed from one village to another. Their social instinct leads members of one village to assist those of another when in trouble. Thus, if a vizcachera is covered over with earth in order to destroy the animals within, Vizcachas from distant burrows will subsequently be found zealously digging out their friends. The hospitality of the Vizcacha does not, however, extend to his burrow; he has a very strong feeling with regard to the sanctity of the burrow. A Vizcacha never enters another's burrow, and if by chance driven into one by dogs will emerge speedily, apparently finding that the danger within is greater than the danger without. In connection with the sociability of the Vizcacha, we must take into consideration the fact that Vizcachas possess a wonderfully varied and expressive language, and are engaged in perpetual discussion all night long.[86]

[86] The Vizcacha has been carefully studied by Mr. W. H. Hudson, whose account has here been closely followed, Proceedings of the Zoological Society, 1872, and Naturalist in La Plata, 1892, pp. 289-313.

Burrows with barns adjoined.—Certain Rodents have carried hollow dwellings to great perfection. Among these the Hamster of Germany (Cricetus frumentarius) is not the least ingenious. To his dwelling-room he adds three or four storehouses for the amassed provisions of which I have already had occasion to speak. The burrow possesses two openings: one, which the animal prefers to use, which sinks vertically into the soil; the other, the passage of exit with a gentle and very winding slope. The bottom of the central room is carpeted with moss and straw, which make it a warm and pleasant home. A third tunnel starts from this sleeping chamber, soon forking and leading to the wheat barns. Thus during the winter the Hamster has no pressing need to go out except on fine days for a little fresh air. He has everything within his reach, and can remain shut up with nothing to fear from the severity of the season.

Dwellings hollowed out in wood.—It is not only the soil which may serve for retreat; wood serves as an asylum for numerous animals, who bore it, and find in it both food and shelter. In this class must be placed a large number of Worms, Insects, and Crustaceans. One of these last, the Chelura terebrans, a little Amphipod, constitutes a great danger for the works of man. It attacks piles sunken to support structures, and undermines them to such a degree that they eventually fall. Wood is formed of concentric layers alternately composed of large vessels formed during the summer, and smaller vessels formed during the winter. The latter zones are more resistant, the former are softer. When one of these Crustaceans attacks a pile, it first bores a little horizontal passage, stopping at a layer of summer-growth. It there hollows a large grotto, leaving here and there pillars of support. It lays in this space. The new generation working around the parents increases the space and feeds on the wood removed. A second generation is produced, and the inhabitants become pressed for space. The new-born pierce numerous passages and penetrate towards the interior of the pile as far as the next summer layer. There they spread themselves, always boring; they construct new rooms like the first, and arrange pillars here and there. Their descendants gain the subjacent zone, and so the process goes on. During this time the early ancestors who hollowed the surface dwellings have died, and the holes which they made are no longer habitable; but they have all contributed to diminish the resistance of the wood, and this continues as long as the race which they produced makes its way towards the centre of the stake.



An insect, the Xylocopa violacea (Fig. 22), related to our Humble-bee, from which it differs in several anatomical characters, and by the dark violet tint of its wings, brings an improvement to the formation of the shelter which it makes in wood for its larvae. Instead of hollowing a mere retreat to place there all its eggs indiscriminately, it divides them into compartments, separated by horizontal partitions. It is the female alone who accomplishes this task, connected with the function of perpetuating the race. She chooses an old tree-trunk, a pole, or the post of a fence, exposed to the sun and already worm-eaten, so that her labour may be lightened. She first attacks the wood perpendicularly to the surface, then suddenly turns and directs downwards the passage, the diameter of which is about equal to the size of the insect's body. The Xylocopa thus forms a tube about thirty centimetres in length. Quite at the bottom she places the first egg, leaving beside it a provision of honey necessary to nourish the larva during its evolution; she then closes it with a partition. This partition is made with fragments of the powder of wood glued together with saliva. A first horizontal ring is applied round the circumference of the tube; then in the interior of this first ring a second is formed, and so on continuously, until the central opening, more and more reduced, is at last entirely closed up. This ceiling forms the floor for the next chamber, in which the female deposits a new egg, provided, like the other, with abundant provisions. The same acts are repeated until the retreat becomes transformed into a series of isolated cells in which the larvae can effect their development, and from which they will emerge either by themselves perforating a thin wall which separates them from daylight, or by an opening which the careful mother has left to allow them to attain liberty without trouble.[87]

[87] Reaumur, Memoires pour servir a l'histoire des Insectes, pp. 97 et seq.

Woven dwellings.—The second class of habitation, which I have called the woven dwelling, proceeds at first from the parcelling up of substances, then of objects capable of being entangled like wisps of wood or straw, then of fine and supple materials which the artisan can work together in a regular manner, that is to say by felting or weaving. Facts will show us the successive stages of improvement which have been introduced into this industry. I will begin with the more rudimentary.

Rudiments of this industry.—There are, first, cases in which the will of the animal does not intervene, or at least is very slightly manifested. The creature is found covered and protected by foreign bodies which are often living beings. Spider-crabs (Maia), for example, have their carapaces covered with algae and hydroids of all sorts. Thus garnished, the Crustaceans have the advantage of not being recognised from afar when they go hunting, since beneath this fleece they resemble some rock. H. Fol has observed at Villefranche-sur-Mer a Maia so buried beneath this vegetation that it was impossible at first sight to distinguish it from the stones around. Under these conditions the animal submits to a shelter rather than creates it. Yet it is not so passive as one might at first be led to suppose. When the algae which flourish on its back become too long and impede or delay its progress, it tears them off with its claws and thoroughly cleans itself. The carapace being quite clean, the animal finds itself too smooth and too easy to distinguish from surrounding objects; it therefore takes up again fragments of algae and replaces them where they do not delay to take root like cuttings and to flourish anew. This culture is therefore intentional; the crab directs it and arrests its exuberance; it is no more the victim of it than the gardener is the slave of the vegetables which he waters day by day. From generation to generation this crab has acquired the habit, the instinct if one prefers, of thus covering itself so that it may be confused with neighbouring objects. Naturally it is ignorant of botany, and knows nothing of cuttings. If placed in an aquarium with little fragments of paper it will seize them and place them on its back, as it would have done with algae, without troubling as to whether they become fixed or not. In spite of this lack of judgment, we cannot fail to recognise in this Maia a certain ingenuity in self-concealment.



The Sponge-crab (Dromia vulgaris) also practises this method of shelter. It seizes a large sponge and maintains it firmly over its carapace with the help of the posterior pair of limbs. The sponge continues to prosper and to spread over the Crustacean who has adopted it. (Fig. 23.) The two beings do not seem to be definitely fixed to each other; the contact of a sudden wave will separate them. When the divorce is effected, the Dromia immediately throws itself on its cherished covering and replaces it. M. Kuenckel d'Herculais tells of one of these curious crustaceans which delighted the workers in the laboratory of Concarneau. The need for covering themselves experienced by these Crabs is so strong that in aquariums when their sponge is taken away they will apply to the back a fragment of wrack or of anything which comes to hand. A little white cloak with the arms of Brittany was manufactured for one of these captives, and it was very amusing to see him put on his overcoat when he had nothing else wherewith to cover himself.[88]

[88] Brehm, edition Francaise, Crustaces, p. 738.

In these two cases which I have brought forward to exhibit the rudiments of this industry, the animals' reflection and will play but a small part; even in the Dromia custom is so inveterate in the race that it has reacted on the animal's organisation, and its four posterior legs are profoundly modified for the purpose of firmly holding the sheltering sponge; they no longer serve for swimming or walking. The animals of which I have now to speak possess more initiative; although all do not act with the same success, or show themselves equally skilful. Let us turn first to the least experienced.

An Australian bird, the Catheturus Lathami, as described by Gould, is still in the rudiments, and limits itself to preparing an enormous pile of leaves. It begins its work some weeks before laying its eggs; with its claws it pushes behind it all the dead leaves which fall on the earth and brings them into a heap. The bird throws new material on the summit until the hole is of suitable height. This detritus ferments when left to itself, and a gentle heat is developed in the centre of the edifice. The Catheturus returns to lay near this coarse shelter; it then takes each egg and buries it in the heap, the larger end uppermost. It places a new layer above, and quits its labour for good. Incubation takes place favoured by the uniform heat of this decomposing mass, hatching is produced, and the young emerge from their primitive nest.



Birds are not alone in constructing temporary dwellings in which to lay their eggs; some Fish are equally artistic in this kind of industry, and even certain Reptiles. The Alligator of the Mississippi would not perhaps at first be regarded as a model of maternal foresight. Yet the female constructs a genuine nest. She seeks a very inaccessible spot in the midst of brushwood and thickets of reeds. With her jaw she carries thither boughs which she arranges on the soil and covers with leaves. She lays her eggs and conceals them with care beneath vegetable remains. Not yet considering her work completed, she stays in the neighbourhood watching with jealous eye the thicket which shelters the dear deposit, and never ceases to mount guard threateningly until the day when her young ones can follow her into the stream.

A hymenopterous relative of the Bees, the Megachile, cuts out in rose-leaves fragments of appropriate form which it bears away to a small hole in a tree, an abandoned mouse nest or some similar cavity. There it rolls them, works them up, and arranges them with much art, so as to manufacture what resemble thimbles, which it fills with honey and in which it lays.[89] (Fig. 24.)

[89] Reaumur, Memoires pour servir a l'histoire des Insectes, pp. 97 et seq.

The Anthocopa acts in a similar manner, carpeting the holes of which it takes possession with the delicate petals of the corn poppy.

The retreats of nocturnal birds of prey do not differ in method of construction from these two kinds of nests. They are holes in trees, in ruins, in old walls, and are lined with soft and warm material. These dwellings are related, not to the type of the hollowed cave, but to that of the habitation manufactured from mingled materials. They constitute an inferior form in which the pieces are not firmly bound together but need support throughout. The cavity is the support which sustains the real house.

Dwellings formed of coarsely-entangled materials.—Diurnal birds of prey are the first animals who practise skilfully the twining of materials. Their nests, which have received the name of eyries, are not yet masterpieces of architecture, and reveal the beginning of the industry which is pushed so far by other birds. Usually situated in wild and inaccessible spots, the young are there in safety when their parents are away on distant expeditions. The abrupt summits of cliffs and the tops of the highest forest trees are the favourite spots chosen by the great birds of prey. The eyrie generally consists of a mass of dry branches which cross and mutually support one another, constituting a whole which is fairly resistant.

Even these primitive nests are not, however, without more complicated details of interest. Thus Mr. Denis Gale wrote to Bendire concerning the Golden Eagle in America: "Here in Colorado, in the numerous glades running from the valleys into the foothills, high inaccessible ledges are quite frequently met with which afford the Eagles secure sites for their enormous nests. I know of one nest that must contain two waggon-loads of material. It is over seven feet high, and quite six feet wide on its upper surface. In most cases the cliff above overhangs the site. At the end of February or the beginning of March, the needful repairs to the nest are attended to, and the universal branch of evergreen is laid upon the nest, seemingly for any purpose save that of utility. This feature has been present in all the nests I have examined myself, or have had examined by others; it would seem to be employed as a badge of occupancy."[90] This curious feature is also found in the nests of the Bald or American Eagle. Thus Dr. W. L. Ralph furnished Bendire with the following observations made in Florida on the dwellings of this, the national bird of the United States:—"The nests are immense structures, from five to six feet in diameter, and about the same in depth, and so strong that a man can walk around in one without danger of breaking through; in fact, my assistant would always get in the nest before letting the eggs down to me. They are composed of sticks, some of which are two or three inches thick, and are lined with marsh grass or some similar material. There is usually a slight depression in the centre, where the eggs are placed, but the edge of the nest extends so far beyond this that it is almost impossible to see the bird from below, unless it has its head well up. I have frequently found foreign substances in their nests, usually placed on the edges of it, the object of which I cannot account for. Often it would be a ball of grass, wet or dry, sometimes a green branch from a pine tree, and again a piece of wood, bark, or other material. It seemed as if they were placed in the nests as if to mark them. From its frequent occurrence, at least, it seemed to me as if designedly done."[91]

[90] Life Histories of North American Birds, 1892, p. 265.

[91] Life Histories of American Birds, p. 275.

The abodes of Squirrels, though exhibiting more art, are constructions of the same nature; that is to say, they are formed of interlaced sticks. This animal builds its home to shelter itself there in the bad season, to pass the night in it, and to rear its young. Very agile, and not afraid of climbing, it places its domicile near the tops of our highest forest trees. Rather capricious also, and desiring change of residence from time to time, it builds several of them; at least three or four, sometimes more. The materials which it needs are collected on the earth among fallen dead branches, or are torn away from the old abandoned nest of a crow or some other bird. The Squirrel firsts builds a rather hollow floor by intermingling the fragments of wood which it has brought. In this state its dwelling resembles a magpie's nest. But the fastidious little animal wishes to be better protected and not thus to sleep in the open air. Over this foundation he raises a conical roof; the sticks which form it are very skilfully disposed, and so well interlaced that the whole is impenetrable to rain. The house must still be furnished, and this is done with oriental luxury; that is to say, the entire furniture consists of a carpet, a carpet of very dry moss, which the Squirrel tears from the trunks of trees, and which it piles up so as to have a soft and warm couch. An entrance situated at the lower part gives access to the aerial castle; it is usually directed towards the east. On the opposite side there is another orifice by which the animal can escape if an enemy should invade the principal entrance. In ordinary times also it serves to ventilate the chamber by setting up a slight current of air. The Squirrel greatly fears storms and rain, and during bad weather hastens to take refuge in his dwelling. If the wind blows in the direction of the openings, the little beast at once closes them with two stoppers of moss, and keeps well shut in as long as the storm rages.