Chapter VI: Dwellings (2)

_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 (_Maïa_), for example, have their carapaces covered with algæ 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 _Maïa_ 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 algæ 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 algæ 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 algæ, without troubling as to whether they become fixed or not. In spite of this lack of judgment, we cannot fail to recognise in this _Maïa_ 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. Künckel 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, édition Française, _Crustacés_, 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] Réaumur, _Memoires pour servir à 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 aërial 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.

The great Anthropoid Apes have found nothing better for shelter than the Squirrels' method. It must, however, be taken into account that they have much more difficulty in arranging and maintaining much heavier rooms, and in building up a shelter with larger surface.

The Orang-outang, which lives in the virgin forests of the Sunda Archipelago, does not feel the need of constructing a roof against the rain. He is content with a floor established in the midst of a tree, and made of broken and interlaced branches. He piles up on this support a considerable mass of leaves and moss; for the Orang does not sleep seated like the other great apes, but lies down in the manner of Man, as has often been observed when he is in captivity. When he feels the cold he is ingenious enough to cover himself with the leaves of his couch.

In Upper and Lower Guinea the Chimpanzee (_Troglodytes niger_) also establishes his dwelling on trees. He first makes choice of a large horizontal branch, which constitutes a sufficient floor for the agile animal. Above this branch he bends the neighbouring boughs, crosses them, and interlaces them so as to obtain a sort of framework. When this preliminary labour is accomplished, he collects dead wood or breaks up branches and adds them to the first. Before commencing he had taken care when choosing the site that the whole was so arranged that a fork was within reach to sustain the roof. He thus constructs a very sufficient shelter. These apes are sociable and prefer to live in each other's neighbourhood. They even go on excursions in rather large bands. Notwithstanding this, more than one or two cabins are never seen on the same tree; perhaps this is because the complicated conditions required for the construction are not likely to be realised several times on the same tree; perhaps also it is a desire for independence which impels the Chimpanzees not to live too near to each other.[92]

[92] Savage, "Observations on the External Characters and
Habits of the _Troglodytes niger_," _Boston Journal Nat.
Hist._, 1843, pp. 362-376.

The _Troglodytes calvus_, a relative of the preceding, inhabiting the same regions, as described by Du Chaillu, shows still more skill in raising his roof. A tree is always chosen for support. He breaks off boughs and fastens them by one end to the trunk, by the other to a large branch. To fix all these pieces he employs very strong creepers, which grow in abundance in his forests. Above this framework, which indicates remarkable ingenuity, the animal piles up large leaves, forming in layers well pressed down and quite impenetrable to the rain. The whole has the appearance of an open parasol. The ape sits on a branch beneath his handiwork, supporting himself against the trunk with one arm. He has thus an excellent shelter against the mid-day sun as well as against tropical showers. Male and female each possess a dwelling on two neighbouring trees, the principle of conjugal cohabitation not being admitted in this species. As to the child, it appears that it sleeps near its mother, until it is of age to lead an independent life.

There exists in Australia, the country of zoological singularities, a bird with very curious customs. This is the Satin Bower-bird. The art displayed in this bird's constructions is not less interesting than the sociability he gives evidence of, and his desire to have for his hours of leisure a shelter adorned to his taste. The bowers which he constructs, and which present on a small scale the appearance of the arbours in our old gardens, are places for re-union and for warbling and courtship, in which the birds stay during the day, when no anxiety leads them to disperse. They are not, properly speaking, nests built for the purpose of rearing young; for at the epoch of love each couple separates and constructs a special retreat in the neighbourhood of the bower. These shelters are always situated in the most retired parts of the forest, and are placed on the earth at the foot of trees. Several couples work together to raise the edifice, the males performing the chief part of the work. At first they establish a slightly convex floor, made with interlaced sticks, intended to keep the place sheltered from the moisture of the soil. The arbour rises in the centre of this first platform. Boughs vertically arranged are interlaced at the base with those of the floor. The birds arrange them in two rows facing each other; they then curve together the upper extremities of these sticks, and fix them so as to obtain a vault. All the prominences in the materials employed are turned towards the outside, so that the interior of the room may be smooth and the birds may not catch their plumage in it. This done, the little architects, to embellish their retreat, transport to it a number of conspicuous objects, such as very white stones from a neighbouring stream, shells, the bright feathers of the parroquet, whatever comes to their beak. All these treasures are arranged on the earth, before the two entries to the bower, so as to form on each side a carpet, which is not smooth, but the varied colours of which rejoice the eye. The prettiest treasures are fixed into the wall of the hut. These houses of pleasure, with all their adornments, form a dwelling very much to the taste of this winged folk, and the birds pass there the greater part of the day, preening their feathers and narrating the news of the forest. Bower-birds' clubs are drawing-rooms raised at the common expense by all who frequent them. The Spotted Bower-bird, the _Chlamydera maculata_, which also lives in the interior of Australia, exercises this method of construction with equal success. The bowers built by these birds may be one metre in length; this is on a very luxurious scale, the animal itself only measuring twenty-five centimetres. In this species, as among other Bower-birds, the bowers are not the labour and the property of a single couple; they are the result of the collaboration of several households, who come together to shelter themselves there. These birds feed only on grains, so that it is to a very pronounced taste for collecting that we must attribute this mania of piling up before the entrance of the bower white stones, shells, and small bones. (Fig. 25.) These objects are intended solely for the delight of these feathered artists. They are very careful also only to collect pieces which have been whitened and dried by the sun.[93]

[93] Gould first accurately described the habits of the
Bower-birds, _Proceed. Zool. Soc._; _London_, 1840, p. 94;
also _Handbook to the Birds of Australia_ (1865), vol. i.
pp. 444-461. See also Darwin's _Descent of Man_ (1881), pp.
381 and 413-414.

Certain Humming-birds also, according to Gould, decorate their dwellings with great taste. "They instinctively fasten thereon," he stated, "beautiful pieces of flat lichen, the larger pieces in the middle, and the smaller on the part attached to the branch. Now and then a pretty feather is intertwined or fastened to the outer sides, the stem being always so placed that the feather stands out beyond the surface."[94]

[94] Gould, _Introduction to the Trochilidæ_, 1861, p. 19.

_Dwellings woven of flexible substances._--In spite of their lack of skill and the inadequacy of their organs for this kind of work, Fish are not the most awkward architects. The species which construct nests for laying in are fairly numerous; the classical case of the Stickleback is always quoted, but this is not the only animal of its class to possess the secret of the manufacture of a shelter for its eggs.

A fish of Java, the Gourami (_Osphronemus olfax_), establishes an ovoid nest with the leaves of aquatic plants woven together. It makes its work about the size of a fist, takes no rest until it is completed, and is able to finish it in five or six days. It is the male alone who weaves this dwelling; when it is ready a female comes to lay there, and generally fills it; it may contain from six hundred to a thousand eggs.

In the sea of Sargasso lives a fish which has received the name of the _Antennarius marmoratus_. Its flattened and monstrous head gives it a strange aspect, and it is marbled with brown and yellow. These colours are those of the tufts of floating seaweed around it, and, thanks to this arrangement, it can easily hide itself amid them without being recognised from afar. This animal constructs for its offspring a fairly safe retreat. The materials which it employs are tufts of Sargasso so abundant in this portion of the Atlantic. It collects all the filaments, and unites them solidly by surrounding them with viscous mucus which it secretes and which hardens. When its work is sufficiently firm not to be destroyed by the waves it lays its eggs in it, and the floating nest is abandoned to its fate. The little ones come out and find within it a sufficient protection for their early age. These dwellings thus floating on the surface of the sea are rounded and about the size of a cocoa-nut.

In Guiana and Brazil another species, the _Choestostomus pictus_, is found, which is equally skilful. With aquatic plants it constructs a spherical nest and arranges it in the midst of the reeds, level with the water. At the lower part a hole is left, through which the female comes to lay. After fertilisation, the couple, as is rarely found among fish, remain in the neighbourhood of their offspring to assist them if necessary. This praiseworthy sentiment is often the cause of their ruin. The inhabitants of the banks speculate on the love of these fish for their offspring to gain possession of them. It is sufficient to place a basket near the entrance of the dwelling, which is then lightly struck. The animal, threatened in its affections, darts furiously forward with bristling spines and throws itself into the trap.

It is scarcely necessary to recall the skilful art with which the Stickleback which inhabits all our streams plaits its nest and remains sentinel near it. (Fig. 26.) This fish has indeed monopolised our admiration, and is considered as the most skilful, if not the only aquatic architect. Yet, besides those which I have already mentioned, there is one which equals the Stickleback in the skill it displays in constructing a shelter for its spawn. This is the _Gobius niger_ met on our coasts, especially in the estuaries of rivers. The male interlaces and weaves the leaves of algæ, etc., and when he has finished his preparations, he goes to seek females, and leads them one by one to lay in the retreat he has built. Then he remains in the neighbourhood until the young come out, ready to throw himself furiously with his spines on any imprudent intruders.

_Dwellings woven with greater art._--Without doubt the class of Birds furnishes the most expert artisans in the industry of the woven dwelling. In our own country we may see them seeking every day to right and left, carrying a morsel of straw, a pinch of moss, a hair from a horse's tail, or a tuft of wool caught in a bush. They intermingle these materials, making the framework of the construction with the coarser pieces, keeping those that are warmer and more delicate for the interior. These nests, attached to a fork in a branch or in a shrub, hidden in the depth of a thicket, are little masterpieces of skill and patience. To describe every form and every method would fill a volume. But I cannot pass in silence those which reveal a science sure of itself, and which are not very inferior to what man can do in this line. The Lithuanian Titmouse (_Ægithalus pendulinus_), whose works have been well described by Baldamus, lives in the marshes in the midst of reeds and willows in Poland, Galicia, and Hungary. Its nest, which resembles none met in our own country, is always suspended above the water, two or three metres above the surface, fixed to a willow branch.[95] All individuals do not exhibit the same skill in fabricating their dwelling; some are more careful and clever than others who are less experienced. Some also are obliged by circumstances to hasten their work. It frequently happens that Magpies spoil or even altogether destroy with blows of their beaks one of these pretty nests. The unfortunate couple are obliged to recommence their task, and if this accident happens two or three times to the same household, it can easily be imagined that, discouraged and depressed by the advancing season, they hasten to build a shelter anyhow, only doing what is indispensable, and neglecting perfection. However this may be, the nests which are properly finished have the form of a purse, twenty centimetres high and twelve broad. (Fig. 27.) At the side an opening, prolonged by a passage which is generally horizontal, gives access to the interior. Sometimes another opening is found without any passage. Every nest in the course of construction possessed this second entry, but it is usually filled up when the work is completed. When the bird has resolved to establish its retreat, it first chooses a hanging branch presenting bifurcations which can be utilised as a rigid frame on which to weave the lateral walls of the habitation. It intercrosses wool and goat's hair so as to form two courses which are afterwards united to each other below, and constitute the first sketch of the nest, at this moment like a flat-bottomed basket. This is only the beginning. The whole wall is reinforced by the addition of new material. The architect piles up down from the poplar and the willow, and binds it all together with filaments torn from the bark of trees, so as to make a whole which is very resistant. Then a couch is formed by heaping up wool and down at the bottom of the nest.

[95] Baldamus, _Beiträge zur Oologie und Nidologie_, 1853,
pp. 419-445.

The American Baltimore Oriole, also called the Baltimore Bird, is a distinguished weaver. With strong stalks and hemp or flax, fastened round two forked twigs corresponding to the proposed width of nest, it makes a very delicate sort of mat, weaving into it quantities of loose tow. The form of the nest might be compared to that of a ham; it is attached by the narrow portion to a small branch, the large part being below. An opening exists at the lower end of the dwelling, and the interior is carefully lined with soft substances, well interwoven with the outward netting, and it is finished with an external layer of horse-hair, while the whole is protected from sun and rain by a natural canopy of leaves.

The Rufous-necked Weaver Bird, as described by Brehm, shows itself equally clever. Its nest is woven with extreme delicacy, and resembles a long-necked decanter hung up with the opening below. From the bottom of the decanter a strong band attaches the whole to the branch of a tree. (Fig. 28.) The Yellow Weaver Bird of Java, as described by Forbes, constructs very similar retort-shaped nests.[96]

[96] H. O. Forbes, _A Naturalist's Wanderings in the Eastern
Archipelago_, 1885, pp. 56-58.

These birds have no monopoly of these careful dwellings; a considerable number of genera have carried this industry to the same degree of perfection.

When animals apply themselves in association to any work, they nearly always exhibit in it a marked superiority over neighbouring species among whom the individuals work in isolation. The construction of dwellings is no exception, and the nests of the Sociable Weaver Birds of South Africa are the best constructed that can be found. These birds live together in considerable colonies; the members of an association are at least two hundred in number, and sometimes rise to five hundred. The city which they construct is a marvel of industry. They first make with grass a sloping roof; giving it the form of a mushroom or an open umbrella, and they place it in such a way that it is supported by the trunk of a tree and one or two of the branches. (Fig. 29.) This thatch is prepared with so much care that it is absolutely impenetrable to water. Beneath this protecting shelter each couple constructs its private dwelling. All the individual nests have their openings below, and they are so closely pressed against one another that on looking at the construction from beneath, the divisions cannot be seen. One only perceives a surface riddled with holes like a skimmer; each of these holes is the door of a nest. The work may endure for several years; as long as there is room beneath the roof the young form pairs near their cradle; but at last, as the colony continues to increase, a portion emigrate to found a new town on another tree in the forest.[97]

[97] An early description of this bird is to be found in W.
Paterson's _Narrative of Four Journeys into the Country of
the Hottentots_, 1789; also in Le Vaillant's _Second Voyage
dans l'intérieur de l'Afrique_, 1803, t. iii., p. 322.

The industry of the woven dwelling does not flourish among mammals; but there is one which excels in it. This is the Dwarf Mouse (_Mus minutus_), certainly one of the smallest Rodents. It generally lives amidst reeds and rushes, and it is perhaps this circumstance which has impelled it to construct an aërial dwelling for its young, not being able to deposit them on the damp and often flooded soil. This retreat is not used in every season; its sole object is for bringing forth the young. It is therefore a genuine nest, not only by the manner in which it is made, but by the object it is intended to serve. The mouse chooses in the midst of its usual domain a tuft with leaves more or less crossed; but not too inextricable, so that there may remain in the midst an empty space, in the centre of which the work will be arranged. Great ingenuity is shown in the preliminaries; the mouse simplifies its task by utilising material within its reach instead of going afar to collect them with trouble. The little animal examines the thicket, and on reflection chooses some thirty leaves which appear suitable. Then, without detaching them, it tears each into seven or eight threads which are held together by the base, and remain attached to the reeds. It is a clever idea to avoid losing a natural point of support. The little bands being thus prepared, they are interlaced and crossed with much art, the animal comes and goes, placing first one of them, then another above, taken from a different leaf. It has soon woven a ball about the size of the fist, and hollowed out the interior. (Fig. 30.) Delicate materials are not lacking around to make a soft bed. The mouse gleans and constantly brings in the light down of the willow, grains with cottony crests, and the petals of flowers. This is all carefully fitted, and when the edifice is completed the female retires into it to bring forth her young, which are there well sheltered against the dangers without, and the caprices of storms and floods. The nest is made with as much delicacy as that of any bird, and no other mammal except Man is capable of executing such weaver's work.

_The art of sewing among birds._--There are birds which have succeeded in solving a remarkable difficulty. Sewing seems so ingenious an art that it must be reserved for the human species alone. Yet the Tailor Bird, the _Orthotomus longicauda_, and other species possess the elements of it. They place their nests in a large leaf which they prepare to this end. With their beaks they pierce two rows of holes along the two edges of the leaf; they then pass a stout thread from one side to the other alternately. With this leaf, at first flat, they form a horn in which they weave their nest with cotton or hair. (Fig. 31.) These labours of weaving and sewing are preceded by the spinning of the thread. The bird makes it itself by twisting in its beak spiders' webs, bits of cotton, and little ends of wool. Sykes found that the threads used for sewing were knotted at the ends.[98] It is impossible not to admire animals who have skilfully triumphed over all the obstacles met with in the course of these complicated operations.[99]

[98] _Catalogue of Birds, etc._, p. 16.

[99] Tristram, "On the Ornithology of Northern Africa," _Isis_, 1859-60.

Certain Spiders, while they do not actually sew in the sense that they perforate the leaves they use to build their nest, and draw the thread through them, yet subject the leaves to an operation which cannot well be called anything else but sewing it.[100]

[100] McCook describes, and gives good illustrations of,
these nests in various stages of progress, _American
Spiders_, vol i. p. 302.

_Modifications of dwellings according to season and climate._--A certain number of facts show that these various industries are not fixed and immutable instincts imposed on the species. Certain Birds change the form of their dwelling according to the climate, or according to the season in which they inhabit it. For example, the Crossbill, _Loxia tænioptera_ (Fig. 32), does not build its nest according to the same rules in Sweden as in France. It builds in every season. The winter shelter is spherical, constructed with very dry lichens, and it is very large. A very narrow opening, just sufficient for the passage of the owner, prevents the external cold from penetrating within. The summer nests are much smaller, in consequence of a reduction in the thickness of the walls. There is no longer need to fear that the cold will come through them, and the animal gives itself no superfluous trouble.

Again, the Baltimore Oriole, which inhabits both the Northern and Southern States of North America, knows very well how to adapt his manner of work to the external circumstances in which he lives. Thus, in the Southern States the nest is woven of delicate materials united in a rather loose fashion, so that the air can circulate freely and keep the interior fresh; it is lined with no warm substance, and the entrance is turned to the west so that the sun only sends into it the oblique evening rays. In the north, on the contrary, the nest is oriented to the south to profit by all the warm sunshine; the walls are thick, without interstices, and the dwelling is carpeted in the warmest and softest manner. Even in the same region there is great diversity in the style, neatness, and finish of the nests, as well as in the materials used. Skeins of silk and hanks of thread have frequently been found in the Baltimore Bird's nest, so woven up and entangled that they could not be withdrawn. As such materials could not be obtained before the introduction of Europeans, it is evident that this bird, with the sagacity of a good architect, knows how to select the strongest and best materials for his work. Many other facts might be quoted, but these suffice to show that the species is not animated by an inevitable instinct, but that each individual, skilful no doubt by heredity, can modify the methods transmitted to him by his ancestors, according to his own experience and his own judgment.

_Built dwellings._--The built dwelling, the expression of the highest civilisation, still remains to be studied. Man has only known how to construct this kind of shelter at a comparatively late period in his evolution; and among animals we do not find it widely spread, much less so, certainly, than the two foregoing methods, especially the first. The difficulty of this work is greater, and it only arrives at considerable development among very sociable species, since the united efforts of a great number of individuals are needed to carry it on.

There are, however, masons who operate separately; but their constructions are rudimentary. The characteristic of all these works is that they are manufactured with some substance to which the animal gives a determined form while it is still soft, and that in drying it preserves this form and acquires solidity. The matter most usually employed is softened and tempered earth--mortar; but there are animals who use with success more delicate bodies. Two examples will suffice to indicate the nature of these exceptions: the labours of Wasps and those of certain Swallows.

_Paper nests._--Certain Wasps, by the material of their dwellings, approach the Japanese; they build with paper. This paper or cardboard is very strong and supplies a solid support; moreover, being a bad conductor of heat, it contributes to maintain an equable temperature within the nest. The constructions of these insects, though they do not exhibit the geometric arrangement of those of Bees, are not less interesting. The paper which they employ is manufactured on the spot, as the walls of the cells develop. Detritus of every kind enters into its preparation: small fragments of wood, sawdust, etc.; anything is good. These Hymenoptera possess no organ specially adapted to aid them; it is with their saliva that they glue this dust together and make of it a substance very suitable for its purpose. The dwellings often reach considerable size, yet they are always begun by a single female, who does all the work without help until the moment when the first eggs come out; she is thus furnished with workers capable of taking a share in her task. The _Vespa sylvestris_ builds a paper nest of this kind, hanging to the branch of a tree, like a great grey sphere prolonged to a blunt neck. (Fig. 33.) The Hornet's nest is similar in construction.

_Gelatine nests._--These are made by certain Swallows who nest in grottoes or cliffs on the edge of the sea. After having collected from the water a gelatinous substance formed either of the spawn of fish or the eggs of Mollusca, they carry this substance on to a perpendicular wall, and apply it to form an arc of a circle. This first deposit being dry, they increase it by sticking on to its edge a new deposit. Gradually the dwelling takes on the appearance of a cup and receives the workers' eggs. (Fig. 34.) These dwellings are the famous swallows' nests, so appreciated by the epicures of the extreme East, which are edible in the same way as, for example, caviare.

_Constructions built of earth--Solitary masons._--Certain animals, whose dwelling participates in the nature of a hollow cavern, make additions to it which claim a place among the constructions with which we are now occupied.

The _Anthophora parietina_ is in this group; it is a small bee which lives in liberty in our climate. As its name indicates, it prefers to frequent the walls of old buildings and finds a refuge in the interstices, hollowing out the mortar half disintegrated by time. The entrance to the dwelling is protected by a tube curved towards the bottom, and making an external prominence. (Fig. 35.) The owner comes and goes by this passage, and as it is curved towards the earth the interior is protected against a flow of rain, while at the same time the entry is rendered more difficult for _Melectes_ and _Anthrax_. These insects, in fact, watch the departure of the _Anthophora_ to endeavour to penetrate into their nests and lay their eggs there. The gallery of entry and exit has been built with grains of sand, the _débris_ produced by the insect in working. These grains of sand glued together form, on drying, a very resistant wall.[101]

[101] Latreille, "Observations sur l'abeille parietine
(_Anthophora parietina_)," _Annales du Muséum d'Hist.
Nat._, t. iii., 1804, p. 257.

The other animals of which I have to speak are genuine masons, who prepare their mortar by tempering moistened earth. Every one has seen the Swallow in spring working at its nest in the corner of a window. It usually establishes its dwelling in an angle, so that the three existing walls can be utilised, and to have an enclosed space there is need only to add the face. It usually gives to this the form of a quarter of a sphere, and begins it by applying earth more or less mixed with chopped hay against the walls which are to support the edifice. At the summit of the construction a hole is left for entry and exit. During the whole of its sojourn in our country the Swallow uses this dwelling, and even returns to it for many years in succession, as long as its work will support the attacks of time. The faithful return of these birds to their old nest has been many times proved by attaching ribbons to their claws; they have always returned with the distinctive mark.

The _Chalicodoma_, whose name of Mason Bee indicates the industry it exercises, is a hymenopterous relative to our Bees, long since carefully studied by Réaumur. It does not live in societies like the latter, and exhibits individual initiative and skill as great as the swallows. The females accomplish the work which I am about to describe. The little cells which they build are arranged, to the number of eight or ten together, in the most various places; sometimes on a pebble, sometimes on a branch, or, again, on a stone wall. (Fig. 36.) The insect collects earth as fine as possible, such as the dust of a trodden path, and tempers it with its own saliva. It places side by side these little balls of mortar and the work soon takes the form of a cupola, to the edge of which it constantly adds new deposits. The sun quickly dries the hole and gives it the necessary consistence. When the cell has acquired sufficient height, the _Chalicodoma_ abandons its occupation of mason, and visits flowers for pollen and nectar wherewith to fill the little chamber. It goes back to the nest, disgorges its supply, and returns to the field, until the little cup of earth is full to the edge. When the dwelling is thus prepared and provisioned, the insect lays an egg there and closes the upper part with a vault, built by successive deposits over the opening, which is more and more narrowed until it is finally shut up. Having completed a chamber, it passes on to the next, and so on until it has assured the fate of all its descendants.

This hymenopterous insect certainly shows in its acts as an artisan an inevitable instinct: hereditary intelligence has become less personal and less spontaneous. In certain cases, however, the instinct loses its rigidity and automatism. Thus, when a _Chalicodoma_, at the moment of preparing to accomplish its task, finds an old nest, still capable of repair although dilapidated, it does not hesitate to take possession of it and to silence its assumed innate instinct of building. It profits by the work already done, and is content to fill up the cracks or to re-establish the masonry where defective; then it provisions the renewed cells with honey, and lays its eggs in them. In certain circumstances it shows itself still more sparing of trouble, and boldly rebels against the law which seems to be imposed on it by nature. If it feels itself sufficiently strong, the _Chalicodoma_ throws itself on one of its fellows, a peaceful constructor that has almost completed its work; it chases it away, and takes possession of its property to shelter its own eggs. Instead of manufacturing the cell from bottom to top, it has only to complete it. Such acts evidently show the reflection appearing through instinct.

Besides the Swallows, of which I have already spoken, birds offer us several types of skilful construction with tempered earth.

The Flamingo, which lives in marshes, cannot place its eggs on the earth nor in the trunks of trees, which are often absent from its domain. It builds a cone of mud, which dries and becomes very resistant, and it prepares at the summit an excavation open to the air; this is the nest. The female broods by sitting with her legs hanging over the sides of the hillock on which her little family prospers above the waters and the damp soil.

A Perch in the Danube also manufactures a dwelling of dried earth. It gives it the form of an elliptic cupola, and prepares a semicircular opening for entry and exit.

The bird which shows itself the most skilful mason is probably the Oven-Bird (_Furnarius rufus_) of Brazil and La Plata. Its name is owing to the form of the nest which it constructs for brooding, and which has the appearance of an oven. It is very skilful and knows how to build a dome of clay without scaffolding, which is not altogether easy. Having chosen for the site of its labours a large horizontal branch, it brings to it a number of little clay balls more or less combined with vegetable _débris_, works them altogether, and makes a very uniform floor, which is to serve as a platform for the rest of the work. When this is done, and while the foundation is drying, the bird arranges on it a circular border of mortar slightly inclined outwards. This becomes hard; it raises it by a new application, this time inclined inwards. All the other layers which will be placed above this will also be inclined towards the interior of the chamber. As the structure rises, the circle which terminates it above becomes more and more narrow. Soon it is quite small, and the animal, closing it with a little ball of clay, finds itself in possession of a well-made dome. Naturally it prepares an entrance; the form of this is semicircular. But this is not all. In the interior it arranges two partitions: one vertical, the other horizontal, separating off a small chamber. The vertical partition begins at one of the edges of the door, so that the air from without cannot penetrate directly into the dwelling, which is thus protected against extreme variations of temperature. It is in the compartment thus formed that the female lays her eggs and broods, after having taken care to carpet it with a thick layer of small herbs.

"In favourable seasons, the Oven-birds begin building in the autumn," Hudson tells us, "and the work is resumed during the winter whenever there is a spell of mild, wet weather. Some of their structures are finished early in winter, others not until spring, everything depending on the weather and the condition of the birds. In cold, dry weather, and when food is scarce, they do not work at all. The site chosen is a stout horizontal branch, or the top of a post, and they also frequently build on a cornice or the roof of a house; and sometimes, but rarely, on the ground. The material used is mud, with the addition of horse hair or slender fibrous rootlets, which make the structure harder and prevent it from cracking. I have frequently seen a bird engaged in building first pick up a thread or hair, then repair to a puddle, where it was worked into a pellet of mud about the size of a filbert, then carried to the nest. When finished the structure is shaped outwardly like a baker's oven, only with a deeper and narrower entrance. It is always placed very conspicuously, and with the entrance facing a building, if one be near, or if at a roadside it looks towards the road; the reason for this being, no doubt, that the bird keeps a continuous eye on the movements of people near it while building, and so leaves the nest opened and unfinished on that side until the last, and then the entrance is necessarily formed. When the structure has assumed the globular form with only a narrow opening, the wall on one side is curved inwards, reaching from the floor to the dome, and at the inner extremity an aperture is left to admit the bird to the interior or second chamber, in which the eggs are laid. A man's hand fits easily into the first or entrance chamber, but cannot be twisted about so as to reach the eggs in the interior cavity, the entrance being so small and high up. The interior is lined with dry soft grass, and five white pear-shaped eggs are laid. The oven is a foot or more in diameter, and is sometimes very massive, weighing eight or nine pounds, and so strong that, unless loosened by the swaying of the branch, it often remains unharmed for two or three years. A new oven is built every year, and I have more than once seen a second oven built on the top of the first, when this has been placed very advantageously, as on a projection and against a wall."[102]

[102] P. L. Sclater and W. H. Hudson, _Argentine
Ornithology_, 1888, vol. i. pp. 168, 169. See also
Burmeister, "Ueber die Eier und Nester einiger
brasilianischen Vögel," _Cabani's Journal für Ornith._,
1853, pp. 161-177.

_Masons working in association._--Ants have already furnished us with numerous proofs of their intelligence and their prodigious industry. So remote from Man from the anatomical point of view, they are of all animals those whose psychic faculties bring them nearest to him. Sociable like him, they have undergone an evolution parallel to his which has placed them at the head of Insects in the same way as he has become superior to all other Mammals. The brain in Ants as in Man has undergone a disproportionate development. Like Man, they possess a language which enables them to combine their efforts, and there is no human industry in which these insects have not arrived at a high degree of perfection. If in certain parts of the earth human societies are superior to those of Ants, in many others the civilisation of Ants is notably superior. No village of Kaffirs can be compared to a palace of the Termites. The classifications separate these insects (sometimes called "White Ants") from the Ants, since the latter are Hymenoptera, while the former are ranked among the Neuroptera, but their constructions are almost alike, and may be described together. These small animals, relatively to their size, build on a colossal scale compared to Man; even our most exceptional monuments cannot be placed beside their ordinary buildings. (Fig. 37.) The domes of triturated and plastered clay which cover their nests may rise to a height of five metres; that is to say, to dimensions equal to one thousand times the length of the worker. The Eiffel Tower, the most elevated monument of which human industry can boast, is only one hundred and eighty-seven times the average height of the worker. It is three hundred metres high, but to equal the Termites' audacity, it would have to attain a height of 1,600 metres.

The different species of Termite are not equally industrious. The _T. bellicosus_ seems to have carried the art of construction to the highest point. All the individuals of the species are not alike; there exists a polymorphism which produces creatures of three sorts: 1, the _soldiers_, recognised by their large heads and long sharp mandibles, moved by powerful muscles; it is their mission to defend the whole colony against its adversaries, and the wounds they can produce, fatal to creatures of their own size, are painful even to man; 2, the _workers_, who labour as navvies and architects, and take charge of the pupæ: they form the great majority of the community; 3, the _king_ and _queen_. (Fig. 38.) To each nest there is usually only a single fertile and lazy couple. These two personages do absolutely nothing; the soldiers and the workers care for them and bring them food. They have both possessed wings, but these fall off. The queen reigns but does not govern; she lays. The king is simply the husband of the queen. The internal administration of the palace is bound up with the parts played by these three kinds of beings.

The lofty nest, or Termitarium, constitutes a hillock in the form of a cupola. The interior arrangement is very complicated, and at the same time very well adapted to the life of the inhabitants. There are four storeys in all, covered by the general exterior walls. (Fig. 39.) The walls of the dome are very thick; at the base they measure from sixty to eighty centimetres. The clay in drying attains the hardness of brick, and the whole is very coherent. The sentinels of herds of wild cattle choose these tumuli as observatories and do not break them down. The walls of this exterior _enceinte_ are hollowed by galleries of two kinds: some horizontal and giving access from outside to all the storeys; the others mounting spirally in the thickness of the wall to the summit of the dome. When the colony is in full activity, after the construction is completed, these little passages have no further use. They served for the passage of the masons when building the cupola; and they could be utilised again if a breach should be made in the wall. At the lower part these galleries in the wall are very wide, and they sink into the earth beneath the palace to a depth of more than 1 metre 50.