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 sp.a.w.n 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 sh.o.r.e, 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 acc.u.mulate 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 thebottom, 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 coc.o.o.n, 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 pa.s.s 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 carca.s.ses. 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 pa.s.ses 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.
[Ill.u.s.tration: FIG. 20.]
[Ill.u.s.tration: FIG. 21.]
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 ill.u.s.tration (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 isthe 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 ill.u.s.tration, 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 ill.u.s.trated 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 pa.s.sage 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 pa.s.sage 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 a.s.sure 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 pa.s.s 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 pa.s.sage, 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 pa.s.sage with stones and calking the interstices with gra.s.s 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 pa.s.sages, 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 pa.s.sages. 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 una.s.suming 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 pa.s.sages 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 gra.s.sy 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 withthose 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 princ.i.p.al 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 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 acc.u.mulate even at the end of this long pa.s.sage, 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 pa.s.sages 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 a.s.sist 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 sanct.i.ty 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 ama.s.sed 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 pa.s.sage 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 cla.s.s must be placed a large number of Worms, Insects, and Crustaceans. One of these last, the Chelura terebrans, a little Amphipod, const.i.tutes 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 pa.s.sage, stopping at a layer of summer-growth. It there hollows a large grotto, leaving here and there pillars of support. It lays in this s.p.a.ce. The new generation working around the parents increases the s.p.a.ce and feeds on the wood removed. A second generation is produced, and the inhabitants become pressed for s.p.a.ce. The new-born pierce numerous pa.s.sages 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.
[Ill.u.s.tration: FIG. 22.]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 part.i.tions. 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 pa.s.sage, 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 part.i.tion. This part.i.tion is made with fragments of the powder of wood glued together with saliva. A first horizontal ring is applied round the circ.u.mference 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 cla.s.s 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 (Maa), for example, have their carapaces covered with algae andhydroids 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 Maa 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 pa.s.sive 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 Maa a certain ingenuity in self-concealment.
[Ill.u.s.tration: FIG. 23.]
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. Kunckel 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 coa.r.s.e 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 ma.s.s, hatching is produced, and the young emerge from their primitive nest.
[Ill.u.s.tration: FIG. 24.]
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, anabandoned 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 const.i.tute 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 coa.r.s.ely-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 ma.s.s of dry branches which cross and mutually support one another, const.i.tuting 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 alsofound 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 a.s.sistant 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 gra.s.s 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 gra.s.s, 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 pa.s.s 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 theeast. On the opposite side there is another orifice by which the animal can escape if an enemy should invade the princ.i.p.al 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 ma.s.s 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 const.i.tutes 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, sh.e.l.ls, 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 variedcolours 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 pa.s.s 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 p.r.o.nounced taste for collecting that we must attribute this mania of piling up before the entrance of the bower white stones, sh.e.l.ls, 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 Trochilidae, 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 cla.s.sical case of the Stickleback is always quoted, but this is not the only animal of its cla.s.s 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.
[Ill.u.s.tration: FIG. 25.]
In the sea of Sarga.s.so 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 Sarga.s.so 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 a.s.sist 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 inconstructing a shelter for its sp.a.w.n. This is the Gobius niger met on our coasts, especially in the estuaries of rivers. The male interlaces and weaves the leaves of algae, 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.
[Ill.u.s.tration: FIG. 26.]
[Ill.u.s.tration: FIG. 27.]
Dwellings woven with greater art.--Without doubt the cla.s.s 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 coa.r.s.er 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 pa.s.s 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 t.i.tmouse (aegithalus 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 circ.u.mstances 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 pa.s.sage which is generally horizontal, gives access to the interior.
Sometimes another opening is found without any pa.s.sage. Every nest in the course of construction possessed this second entry, but it is usually filled upwhen 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 const.i.tute 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, Beitrage 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 quant.i.ties 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.
[Ill.u.s.tration: FIG. 28.]
[Ill.u.s.tration: FIG. 29.]When animals apply themselves in a.s.sociation 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 a.s.sociation 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 gra.s.s 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"interieur de l"Afrique, 1803, t. iii., p. 322.
[Ill.u.s.tration: FIG. 30.]
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 circ.u.mstance which has impelled it to construct an aerial 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 s.p.a.ce, 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 reflectionchooses 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 pa.s.s 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.