Animal Intelligence Part 18

With this bubble she descends, 'like a globe of quicksilver,' to the opening of her nest, where she liberates it and returns for more.

_The Vagrant or Wolf Spider._--This insect catches its prey by stealthily stalking it until within distance near enough to admit of a sudden dart being successful in effecting capture. Some species, before making the final dart (_e.g. Salticus scenicus_), fix a line of web upon the surface over which they are creeping, so that whether their station is vertical or horizontal with reference to the prey, they can leap fearlessly, the thread in any case preventing their fall. Dr. H. F.

Hutchinson says that he has seen this spider crawling over a looking-gla.s.s stalking its own reflection.[83]

The following is quoted from Buchner:--

Less idyllic than the water-spider is our native hunting-spider (_Dolomedes fimbriata_), which belongs to those species which spin no web, but hunt their victims like animals of prey. As the _Argyroneta_ is the discoverer of the diving-bell, so may this be regarded as the discoverer or first builder of a floating raft. It is not content with hunting insects on land, but follows them on the water, on the surface of which it runs about with ease. It, however, needs a place to rest on, and makes it by rolling together dry leaves and such like bodies, binding them into a firm whole with its silken threads. On this raft-like vessel it floats at the mercy of wind and waves; and if an unlucky water-insect comes for an instant to the surface of the water to breathe, the spider darts at it with lightning speed, and carries it back to its raft to devour at its ease. Thus everywhere in nature are battle, craft, and ingenuity, all following the merciless law of egoism, in order to maintain their own lives and to destroy those of others!

_Trap-door Spiders._--These display the curious instinct of providing their nests with trap-doors. The nest consists of a tube excavated in the earth to the depth of half a foot or more. In all save one species the tube is unbranched; it is always lined with silk, which is continuous with the lining of the trap-door or doors, of which it forms the hinge. In the species which constructs a branching tube, the branch is always single, more or less straight, takes origin at a point situated a few inches from the orifice of the main tube, is directed upwards at an acute angle with that tube, and terminates blindly just below the surface of the soil. At its point of junction with or departure from the main tube it is provided with a trap-door resembling that which closes the orifice of the main tube, and of such a size and arrangement that when closed against the opening of the branch tube it just fills that opening; while when turned outwards, so as to uncork this opening, it just fills the diameter of the main tube: the latter, therefore, is in this species provided with two trap-doors, one at the surface of the soil, and the other at the fork of the branched tube.

Each species of trap-door spider is very constant in building a particular kind of trap-door; but among the different species there are four several kinds of trap-doors to be distinguished. 1st. The single-door cork nest, wherein the trap-door is a thick structure, and fits into the tube like a cork into a bottle. 2nd. The single-door wafer nest, wherein the trap-door is as thin as a piece of paper. 3rd. The double-door unbranched nest, wherein there is a second trap-door situated a few inches below the first one. And 4th, the double-door branched nest already described. In all cases the trap-doors open outwards, and when the nest is placed, as it usually is, on a sloping bank, the trap-door opens upwards; hence there is no fear of its gaping, for gravity is on the side of holding it shut.

The object of the trap-door is to conceal the nest, and for this purpose it is always made so closely to resemble the general surface of the ground on which it occurs, that even a practised eye finds it difficult to detect the structure when closed. In order to make the resemblance to the surrounding objects as perfect as possible, the spider either constructs the surface of its door of a portion of leaf, or weaves moss, gra.s.s, &c., into the texture. Moggridge says,[84]--

Thus, for example, in one case where I had cut out a little clod of mossy earth, about two inches thick and three square on the surface, containing the top of the tube and the moss-covered cork door of _N.

caementaria_, I found, on revisiting the place six days later, that a new door had been made, and that the spider had mounted up to fetch moss from the undisturbed bank above, planting it in the earth which formed the crown of the door. Here the moss actually called the eye to the trap, which lay in the little plain of brown earth made by my digging.

If an enemy should detect the trap-door and endeavour to open it, the spider frequently seizes hold of its internal surface, and, applying her legs to the walls of the tube, forcibly holds the trap-door shut. In the double trap-door species it is surmised that the second trap-door serves as an inner barrier of defence, behind which the spider retires when obliged to abandon the first one. In the branched tube species (which, so far as at present known, only occurs in the south of Europe) it is surmised that the spider, when it finds that an enemy is about to gain entrance at the first trap-door, runs into the branch tube and draws up behind it the second trap-door. The surface of this trap-door, being overlaid with silk like the walls of the tube, is then invisible; so that the enemy no doubt pa.s.ses down the main tube to find it empty, without observing the lateral branch in which the spider is concealed behind the closed door.

As showing that these animals are to no small extent able to adapt their dwellings to unusual circ.u.mstances, I shall here quote the following from Moggridge (_loc. cit._, p. 122):--

Certain nests which were furnished with two doors of the cork type were observed by Mr. S. S. Saunders in the Ionian Islands. The door at the surface of these nests was normal in position and structure, but the lower one was placed at the very bottom of the nest, and inverted, so that, though apparently intended to open downwards, it was permanently closed by the surrounding earth. The presence of a carefully constructed door in a situation which forbade the possibility of its ever being opened seemed, indeed, something difficult to account for. However, it occurred to Mr. Saunders that, as these nests were found in the cultivated ground round the roots of olive trees, they may occasionally have got turned topsy-turvy when the soil was broken up. The spider then, finding her door buried below in the ground and the bottom of the tube at the surface, would have either to seek new quarters or to adapt the nest to its altered position, and make an opening and door at the exposed end. In order to try whether one of these spiders would do this, Mr. Saunders placed a nest, with its occupant inside, upside down in a flower-pot.

After the lapse of ten days a new door was made, exactly as he had conjectured it would be, and the nest presented two doors like those which he had found at first.

The most remarkable fact connected with these animals, if we regard their peculiar instinct from the standpoint of the descent theory, is the wide range of their geographical distribution. In all quarters of the globe species of trap-door spiders are found occurring in more or less localised areas; and as it is improbable that so peculiar an instinct should have arisen independently in more than one line of descent, we can only conclude that the wide dispersion of the species presenting it has been subsequent to the origin and perfecting of the instinct. This conclusion of course necessitates the supposition that the instinct must be one of enormous antiquity; and in this connection it is worthy of remark that we seem to have independent evidence to show that such is the case. It is a principle of evolution that the earlier any structure or instinct appears in the development of the race, the sooner will it appear in the development of the individual; and read by the light of this principle we should conclude, quite apart from all considerations as to the wide geographical distribution of trap-door spiders, that their instincts--as, indeed, is the case with the characteristic instincts of many other species of spiders--must be of immense age. Thus, again to quote Moggridge,--

It seems to be the rule with spiders generally that the offspring should leave the nest and construct dwellings for themselves when very young.

Mr. Blackwall, speaking of British spiders, says:--'Complicated as the processes are by which these symmetrical nets are produced, nevertheless young spiders, acting under the influence of instinctive impulse, display, even in their first attempts to fabricate them, as consummate skill as the most experienced individuals.'

Again, Mr. F. Pollock[85] relates of the young of _Epeira aurelia_, which he observed in Madeira, that when seven weeks old they made a web the size of a penny, and that these nets have the same beautiful symmetry as those of the full-grown spider.

And, speaking of trap-door spiders, Moggridge says,--

I cannot help thinking that these very small nests, built as they are by minute spiders probably not very long hatched from the egg, must rank among the most marvellous structures of this kind with which we are acquainted. That so young and weak a creature should be able to excavate a tube in the earth many times its own length, and know how to make a perfect miniature of the nest of its parents, seems to be a fact which has scarcely a parallel in nature.[86]

Regarding the steps whereby the instinct of building trap-doors probably arose, Buchner quotes Moggridge thus:--

To show, lastly, how various are the transitional forms and gradations so important in deciding upon the gradual origin of the forms of nests, Moggridge also alludes to the similar buildings made by other genera of spiders. _Lycosa Narbonensis_, a spider of Southern France much resembling the Apuleian tarantula, and belonging to the family of the wolf spiders, makes cylindrical holes in the earth, about one inch wide and three or four inches deep, in a perpendicular direction; when they have attained this depth they run further horizontally, and end in a three cornered room, from one to two inches broad, the floor of which is covered with the remnants of dead insects. The whole nest is lined within with a thick silken material, and has at its opening--closed by no door--an above-ground chimney-shaped extension, made of leaves, needles, moss, wood, &c., woven together with spider threads. These chimneys show various differences in their manner of building, and are intended chiefly, according to Moggridge, to prevent the sand blown about by the violent sea-winds from penetrating into the nests. During winter the opening is wholly and continuously woven over, and it is very well possible, or probable, that the process of reopening such a warm covering in the spring, after this opening was three-quarters completed, and was large enough to let the spider pa.s.s out, may have long ago awaked in the brain of some species of spider the idea of making a permanent and moveable door. But from this to the practical construction of so perfect a door as we have learned to know, and even to the building of the exceedingly complicated nest of the _N. Manderstjernae_, through all the gradations which we already know, and which doubtless exist in far greater number, is no great or impossible step.

_General Intelligence._

Coming now to the general intelligence of spiders, I think there can be no reasonable doubt, from the force of concurrent testimony, that they are able to distinguish between persons, and approach those whom they have found to be friendly, while shunning strangers. This power of discrimination, it will be remembered, also occurs among bees and wasps, and therefore its presence in spiders is not antecedently improbable. I myself know a lady who has 'tamed' spiders to recognise her, so that they come out to be fed when she enters the room where they are kept; and stories of the taming of spiders by prisoners are abundant. The following anecdote recorded by Buchner is in this connection worth quoting:--

Dr. Moschkau, of Gohlis, near Leipsic, writes as follows to the author, on August 28, 1876:--'In Oderwitz(?), where I lived in 1873 and 1874, I noticed one day in a half-dark corner of the anteroom a tolerably respectable spider's web, in which a well-fed cross-spider had made its home, and sat at the nest-opening early and late, watching for some flying or creeping food. I was accidentally several times a witness of the craft with which it caught its victim and rendered it harmless, and it soon became a regular duty to carry it flies several times during a day, which I laid down before its door with a pair of pincers. At first this feeding seemed to arouse small confidence, the pincers perhaps being in fault, for it let many of the flies escape again, or only seized them when it knew that they were within reach of its abode. After a while, however, the spider came each time and took the flies out of the pincers and spun them over. The latter business was sometimes done so superficially, when I gave flies very quickly one after the other, that some of the already ensnared flies found time and opportunity to escape. This game was carried on by me for some weeks, as it seemed to me curious. But one day when the spider seemed very ravenous, and regularly flew at each fly offered to it, I began teasing it. As soon as it had got hold of the fly I pulled it back again with the pincers. It took this exceedingly ill. The first time, as I finally left the fly with it, it managed to forgive me, but when I later took a fly right away, our friendship was destroyed for ever. On the following day it treated my offered flies with contempt, and would not move, and on the third day it had disappeared.[87]

Jesse relates the following anecdote, which seems to display on the part of a spider somewhat remote adaptation of means to novel circ.u.mstances.

He confined a spider with her eggs under a gla.s.s upon a marble mantelpiece. Having surrounded the eggs with web,--

She next proceeded to fix one of her threads to the upper part of the gla.s.s which confined her, and carried it to the further end of the piece of gra.s.s, and in a short time had succeeded in raising it up and fixing it perpendicularly, working her threads from the sides of the gla.s.s to the top and sides of the piece of gra.s.s. Her motive in doing this was obvious.

She not only rendered the object of her care more secure than it would have been had it remained flat on the marble, but she was probably aware that the cold from the marble would chill her eggs, and prevent their arriving at maturity: she therefore raised them from it in the manner I have described.[88]

Mr. Belt gives the following account of the intelligence which certain species of South American spiders display in escaping from the terrible hosts of the Eciton ants:--

Many of the spiders would escape by hanging suspended by a thread of silk from the branches, safe from the foes that swarmed both above and below.

I noticed that spiders generally were most intelligent in escaping, and did not, like the c.o.c.kroaches and other insects, take shelter in the first hiding-place they found, only to be driven out again, or perhaps caught by the advancing army of ants. I have often seen large spiders making off many yards in advance, and apparently determined to put a good distance between themselves and the foe. I once saw one of the false spiders, or harvest-men (_Phalangidae_), standing in the midst of an army of ants, and with the greatest circ.u.mspection and coolness lifting, one after the other, its long legs, which supported its body above their reach. Sometimes as many as five out of its eight legs would be lifted at once, and whenever an ant approached one of those on which it stood, there was always a clear s.p.a.ce within reach to put down another, so as to be able to hold up the threatened one out of danger.[89]

Mr. L. A. Morgan, writing to 'Nature' (Jan. 22, 1880), gives an account of a spider conveying a large insect from the part of the web where it was caught to the 'larder,' by the following means. The spider first went two or three times backwards and forwards between the head of the insect and the main strand of the web. After this he went about cutting all the threads around the insect till the latter hung by the head strands alone. The spider then fixed a thread to the tail end, and by this dragged the carca.s.s as far on its way to the larder as the head strands would permit. As soon as these were taut, he made the tail rope fast, went back to the head rope and cut it; then he attached himself to the head and pulled the body towards the larder, until the tail rope was taut. In this way, by alternately cutting the head and tail ropes and dragging the insect bit by bit, he conveyed it safely to the larder.

But the practical acquaintance with mechanical principles which this observation displays is perhaps not so remarkable as that which is sometimes shown by spiders when they find that a widely spread web is not tightly enough stretched, and as a consequence is to an inconvenient extent swayed about by the wind. Under such circ.u.mstances these animals have been observed to suspend to their webs small stones or other heavy objects, the weight of which serves to steady the whole system.

Gleditsch saw a spider so circ.u.mstanced let itself down to the ground by means of a thread, seize a small stone, remount, and fasten the stone to the lower part of its web, at a height sufficient to enable animals and men to walk beneath it. After alluding to this case, Buchner observes (_loc. cit._, p. 318),--

But a similar observation was made by Professor E. H.

Weber, the famous anatomist and physiologist, and was published many years ago in Muller's Journal. A spider had stretched its web between two posts standing opposite each other, and had fastened it to a plant below for the third point. But as the attachment below was often broken by the garden work, by pa.s.sers-by, and in other ways, the little animal extricated itself from the difficulty by spinning its web round a little stone, and fastened this to the lower part of its web, swinging freely, and so to draw the web down by its weight instead of fastening it in this direction by a connecting thread. Carus ('Vergl. Psycho.,' 1866, p.

76) also made a similar observation. But the most interesting observation on this head is related by J.

G. Wood ('Glimpses into Petland'), and repeated by Watson (_loc. cit._, p. 455). One of my friends, says Wood, was accustomed to grant shelter to a number of garden spiders under a large verandah, and to watch their habits. One day a sharp storm broke out, and the wind raged so furiously through the garden that the spiders suffered damage from it, although sheltered by the verandah. The mainyards of one of these webs, as the sailors would call them, were broken, so that the web was blown hither and thither, like a slack sail in a storm. The spider made no fresh threads, but tried to help itself in another way. It let itself down to the ground by a thread, and crawled to a place where lay some splintered pieces of a wooden fence thrown down by the storm. It fastened a thread to one of the bits of wood, turned back with it, and hung it with a strong thread to the lower part of its nest, about five feet from the ground. The performance was a wonderful one, for the weight of the wood sufficed to keep the nest tolerably firm, while it was yet light enough to yield to the wind, and so prevent further injury. The piece of wood was about two and a half inches long, and as thick as a goose-quill. On the following day a careless servant knocked her head against the wood, and it fell down. But in the course of a few hours the spider had found it and brought it back to its place. When the storm ceased, the spider mended her web, broke the supporting thread in two, and let the wood fall to the ground!

If so well-observed a fact requires any further confirmation, I may adduce the following account, which is of the more value as corroborative evidence from the writer not appearing to be aware that the fact had been observed before. This writer is Dr. John Topham, whom the late Dr. Sharpey, F.R.S., a.s.sured me is a competent observer, and who publishes the account in 'Nature' (xi. 18):--

A spider constructed its web in an angle of my garden, the sides of which were attached by long threads to shrubs at the height of nearly three feet from the gravel path beneath. Being much exposed to the wind, the equinoctial gales of this autumn destroyed the web several times.

The ingenious spider now adopted the contrivance here represented. It secured a conical fragment of gravel with its larger end upwards by two cords, one attached to each of its opposite sides, to the apex of its wedge-shaped web, and left it suspended as a moveable weight to be opposed to the effect of such gusts of air as had destroyed the webs previously occupying the same situation.

The spider must have descended to the gravel path for this special object, and having attached threads to a stone suited to its purpose, must have afterwards raised this by fixing itself upon the web, and pulling the weight up to a height of more than two feet from the ground, where it hung suspended by elastic cords.

The excellence of the contrivance is too evident to require further comment.

An almost precisely a.n.a.logous case, with a sketch, is published by another observer in 'Land and Water,' Dec. 12, 1877.

_Scorpions._

Before quitting the Arachnida I must allude to some recent correspondence on the alleged tendency of the scorpion to commit suicide when surrounded by fire. This alleged tendency has long been recognised in popular fables, and has been used by Byron as a poetical metaphor in certain well-known lines. But until the publication of the correspondence to which I allude, no one supposed the tendency in question to have any existence in fact. This correspondence took place in 'Nature' (vol. xi.), and as the subject is an interesting one, I shall reproduce the more important contributions to it _in extenso_. It was opened by Mr. W. G. Biddie as follows:--

I shall feel obliged if you will record in 'Nature' a fact with reference to the common black scorpion of Southern India, which was observed by me some years ago in Madras.

One morning a servant brought to me a large specimen of this scorpion, which, having stayed out too long in its nocturnal rambles, had apparently got bewildered at daybreak, and been unable to find its way home. To keep it safe the creature was at once put into a glazed entomological case. Having a few leisure minutes in the course of the forenoon I thought I would see how my prisoner was getting on, and to have a better view of it the case was placed in a window in the rays of the hot sun. The light and heat seemed to irritate it very much, and this recalled to my mind a story which I had read somewhere that a scorpion, on being surrounded with fire, had committed suicide. I hesitated about subjecting my pet to such a terrible ordeal, but taking a common botanical lens, I focussed the rays of the sun on its back. The moment this was done it began to run hurriedly about the case, hissing and spitting in a very fierce way. This experiment was repeated some four or five times with like results, but on trying it once again, the scorpion turned up its tail and plunged the sting, quick as lightning, into its own back. The infliction of the wound was followed by a sudden escape of fluid, and a friend standing by me called out, 'See, it has stung itself: it is dead;' and sure enough in less than half a minute life was quite extinct. I have written this brief note to show (1) that animals may commit suicide; (2) that the poison of certain animals may be destructive to themselves.

The following corroborative evidence on the subject was then supplied by Dr. Allen Thomson, F.R.S. ('Nature,' vol. xx., p. 577):--

Doubts having been expressed at various times, even by learned naturalists, as to the reality of the suicide or self-destruction of the scorpion by means of its own poison, and these doubts having been again stated in 'Nature,' vol. xx., p. 553, by Mr. B. F.

Hutchinson, of Peshawur, as the result of his own observations, I think it may be useful to give an articulate account of the phenomenon as it has been related to me by an eye-witness, which removes all possible doubt as to its occurrence under certain circ.u.mstances.

While residing many years ago, during the summer months, at the baths of Sulla in Italy, in a somewhat damp locality, my informant together with the rest of the family was much annoyed by the frequent intrusion of small black scorpions into the house, and their being secreted among the bedclothes, in shoes, and other articles of dress. It thus became necessary to be constantly on the watch for these troublesome creatures, and to take means for their removal and destruction. Having been informed by the natives of the place that the scorpion would destroy itself if exposed to a sudden light, my informant and her friends soon became adepts in catching the scorpions and disposing of them in the manner suggested. This consisted in confining the animal under an inverted drinking-gla.s.s or tumbler, below which a card was inserted when the capture was made, and then, waiting till dark, suddenly bringing the light of a candle near to the gla.s.s in which the animal was confined. No sooner was this done than the scorpion invariably showed signs of great excitement, running round and round the interior of the tumbler with reckless velocity for a number of times. This state having lasted for a minute or more, the animal suddenly became quiet, and turning its tail on the hinder part of its body over its back, brought its recurved sting down upon the middle of the head, and piercing it forcibly, in a few seconds became quite motionless, and in fact quite dead. This observation was repeated very frequently; in truth, it was adopted as the best plan of getting rid of the animals. The young people were in the habit of handling the scorpions with impunity immediately after they were so killed, and of preserving many of them as curiosities.

In this narrative the following circ.u.mstances are worthy of attention:--

(1) The effect of light in producing the excitement amounting to despair, which causes the animal to commit self-destruction;