« ForrigeFortsæt »
victim making no struggles whatever ; but if they meet face to face, both enter into a wrestling-match for life or death.
"They plant their true feet firmly on the ground, the body at the same time being elevated, and the two pair of palpi held out in front to ward off the attack. In this attitude they advance and retire, according as either gains a slight advantage, endeavouring to throw each other to one side, so as to expose some vulnerable part, or form an opening for attack; and when this is once effected, the fortunate wrestler instantly takes advantage of it, and rushing in, seizes his adversary behind the thorax, and the combat is ended; the vanquished victim yielding himself without further struggle to his inevitable fate.
"The usual size of an adult specimen of galeodes is about 2. to 24 inches long, and the body or abdomen equal to a thrush's egg. When in motion, the body is elevated off the ground, and the two pair of palpi, or feelers, are stretched out, ready to make a seizure ; it progresses therefore solely upon the true legs, which spring from the thorax, and are six in number. The head is armed with two strong and formidable chelæ, or double jaws, answering to the long cheliform fore-arms of the scorpion .... eyes two, and placed on the top of the head, between the base of the jaws; the colour generally is sandy-brown, and the body soft, and clothed with short mouse-coloured hairs; the limbs, and especially the palpi, are furnished with long coarse hairs. .... In seizing its prey, one pair of jaws keeps hold, while the other is advanced to cut; and they thus alternately advance and hold till the victim is sawed in two. The only sound they emit is a hissing or rustling, caused by the friction of the two pair of chelæ, as they are advanced and withdrawn; this is only heard when the spider is suddenly disturbed or irritated.
Such are the habits and peculiarities of the Galeodes vorara species generally regarded with disgust and aversion. It is found in most parts of India, in the Burman empire and in Afghanistan, where it has been mistaken for the tarantula. In cases where they fix their habitation in a garden, these great spiders have been known to render good service by devouring larvæ, grubs, cockroaches, and other noxious insects ; and there is no reason to doubt that they serve some wise and useful purpose in the general economy of nature.
FOREIGN SPIDERS OF VARIOUS GENERA. Speaking of the zoology of Rio de Janeiro, Mr Darwin observes that the number of spiders, in proportion to insects, is there, as compared with England, very much larger. "The variety of species among the jumping spiders appears almost infinite. The genus, or rather family, of Epeira is here characterised by many singular forms : some species have pointed coriaceous shells, others enlarged and spiny limbs. Every path in the forest is barricaded with the strong yellow web of a species belonging to the same division with the Ē. clavipes of Fabricius, which was formerly said by Sloane to make, in the West Indies, webs so strong as to catch birds. A small and pretty kind of spider, with very long fore-legs, and which appears to belong to an undescribed genus, lives as a parasite on almost every one of these webs. I suppose it is too insignificant to be noticed by the great epeira, and is therefore allowed to prey on the minute insects which, adhering to the lines, would otherwise be wasted. When frightened, this little spider either feigns death by extending its front legs, or suddenly drops from the web.
A large epeira, of the same division with E. tuberculata and conica, is extremely common, especially in dry situations. Its web, which is generally placed among the great leaves of the common agavé, is sometimes strengthened near the centre by a pair or even four zigzag ribbons, which connect two adjoining rays. When any large insect, as a grasshopper or wasp, is caught, the spider, by a dexterous movement, makes it revolve very rapidly, and at the same time emitting a band of thread from its spinners, soon envelops its prey in a case like the cocoon of a silk-worm. The spider now examines the powerless victim, and gives the fatal bite on the hinder part of its thorax; then, retreating, patiently waits till the poison has taken effect. The virulence of this poison may be judged of from the fact, that in half a minute I opened the mesh, and found a large wasp quite lifeless. This spider always stands with its head downward near the centre of this web. When disturbed, it acts differently according to circumstances. If there is a thicket below, it suddenly falls down ; and I have distinctly seen the thread from the spinners lengthened by the animal, while yet stationary, as preparatory to its fall. If the ground is clear beneath, the spider seldom falls, but moves quickly through a central passage from one to the other side. When still further disturbed, it practises a curious manoeuvre : standing in the middle, it violently jerks the web, which is attached to elastic twigs, till at last the whole acquires such a rapid vibratory movement that even the outline of the spider's body becomes indistinct.'
Though it is thus omnipotent over the majority of insects, there are some of these more than a match for the most ferocious spiders, even making their carcasses a regular article of dietary. The same authority mentions a deadly contest which he once witnessed between a pepsis and a large spider of the genus Lycosa. 'The wasp made a sudden dash at its prey, and then flew away. The spider was evidently wounded ; for, trying to escape, it rolled down a little slope, but had still strength sufficient to crawl into a thick tuft of grass. The wasp soon returned, and, surprised at not immediately finding its victim, it then commenced as regular a hunt as ever hound did after fox ; making short semicircular casts, and all the time rapidly vibrating its wings and antennæ. The spider, though well concealed, was soon discovered ; and the wasp, evidently still afraid of its adversary's jaws, after much manœuvring, inflicted two stings on the under side of its thorax. At last, carefully examining with its antennæ the now motionless spider, it proceeded to drag away the body:
The species of which we have yet spoken are strictly solitary in their habits ; indeed, we question whether all spiders are not the same in this respect, being only brought into proximity by favourable locality or abundance of food. Mr Darwin, however, states that he found, near St Té Bajada, many large black spiders, with ruby-coloured marks on their backs, having gregarious habits. "The webs,' says he, 'were placed vertically, as is invariably the case with the genus Epeira. They were separated from each other by a space of about two feet; but were all attached to certain common lines, which were of great length, and extended to all parts of the community. In this manner the tops of some large bushes were encompassed by the united nets. Azara has described a gregarious spider in Paraguay, which Walckenaer thinks must be a theridion, but probably it is an epeira, and perhaps even the same species with mine. I cannot, however, recollect seeing a central nest as large as a hat, in which during autumn, when the spiders die, Azara says the eggs are deposited. As all the spiders which I saw were of the same size, they must have been nearly of the same age. This gregarious habit in so typical a genus as Epeira, among creatures which are so bloodthirsty and solitary that even the two sexes attack each other, is a very singular fact.'
The singularity of the webs of several foreign species has attracted much attention. In Java, some of these are said to be so strong and tough that they are not easily divided without a knife, and in this case quite capable of entangling not only insects, but birds and small quadrupeds. In the Cordilleras, Mr Darwin found nets constructed after the manner of those of our garden-spider; but instead of all the rays being netted, only two were woven together, so that the web was of a wedge-shape. Perhaps the most ingenious exhibition of networking which we have read is that of an Australian spider, related by a correspondent of the Zoologist for January 1846 : 'In the middle of last April I was particularly struck with the singular habits of a spider, which had constructed his web between a high fence and the gable-end of my house [in Sydney]; these being about ten yards from each other, and the web being about midway between them. As soon as the web was finished, the spider procured a leaf, and having rolled it up in the form of an extinguisher, he fixed it in the very centre of the web, with the point upwards. In this domicile he remained at rest until some prey was entangled in the web, when he immediately pounced upon it, and conveyed it to his mansion to be devoured. Whether the object of this singular contrivance was protection from the weather, or concealment from his prey, or both combined, I am unable to say; but it struck me as very ingenious. Had the domicile been placed at the extremity of the lines, the spider would have had at least five yards of line to traverse before reaching the centre of the web, and of course the same distance to return with his prey. One wet and windy night spider and all disappeared.'
With the exception of the Javanese spiders, all that we have yet mentioned weave comparatively small and slender fabrics. This is not the case, however, with a Brazilian spider noticed by Dr Walsh, and apparently the same with the large Epeira found by Mr Darwin in the neighbourhood of Rio de Janeiro ; at least both weave strong yellow webs, and have semi-gregarious habits. The doctor's account of it is as follows: ‘Among the insects is an enormous spider, which I did not observe elsewhere. In passing through an opening between some trees, I felt my head entangled in some obstructions, and on withdrawing it, my straw-hat remained behind. When I looked up, I saw it suspended in the air, entangled in the meshes of an immense cobweb, which was drawn like a veil of thick gauze across the opening, and was expanded from branch to branch of the opposite trees, as large as a sheet ten or twelve feet in diameter. The whole of this space was covered with spiders of the same species, but different sizes, some of them, when their legs were expanded, forming a circle of six or seven inches in circumference. They were particularly distinguished by bright spots. The cords composing the web were of a glossy yellow, like the fibres of silk-worms, and equally strong. I wound off several on a card, and they extended to the length of three or four yards.' Sir James Emerson Tennent tells us of a spider of Ceylon-the Olios Trapobanius-very common in that island, and remarkable for the fiery-red hue of its under surface, that ‘it spins a moderate-sized web, hung vertically between two sets of lines, stretched one above the other athwart the pathways.' 'Some of the cords,' he adds, thus carried horizontally from tree to tree at a considerable height from the ground, are so strong as to cause a painful check across the face when moving quickly against them; and more than once in riding I have had my hat lifted off my head by a single line. One cannot read these accounts without concluding that such a product, if found in abundance, might be successfully applied to some economical purpose. Indeed, the application of spider-web has already been attempted, with various success, to the manufacture of a kind of silk, of which we shall now give some account.
SPIDER-SIL K. The idea of obtaining silk from the produce of the spider occurred first, we believe, to Reaumur, who for that purpose collected the eggbags or cocoons, and not the webs, of the common garden-spider. Having obtained, with some trouble, thirteen ounces of these bags, he had them beaten and washed, to free them from extraneous impurities. After this they were steeped in a solution of soap, nitre, and gum-arabic, and then boiled in the same mixture over a slow fire. Clean warm water was then used to free them from the soap, &c.; and having been laid for some days to dry, they were loosened with the fingers previously to being carded by the common silk-carders. By this process a beautiful ash-coloured silk is said to have been obtained, easy to be spun, and much stronger in the thread than that of the silk-worm. This was woven in a stocking-weaver's loom. The thirteen ounces of bags yielded about four ounces of silk, three of which were sufficient for the manufacture of a pair of stockings. This experiment fully demonstrated the capabilities of spider-silk; but the impossibility of obtaining abundance of the raw material precluded any further application of the discovery. Naturally, the substance is concealed, or torn and scattered about in insignificant quantities; and to rear spiders artificially, as we do the silk-worm, has been found impossible, in consequence of their hostile and ferocious natures. Reaumur placed 5000 in fifty different cells, and fed them on insects and proper juices ; notwithstanding, the larger devoured the smaller, till in a short time only two or three were left in each compartment.
More recently, a gentleman of the name of Rolt received an honorary medal from the London Society of Arts for obtaining silk from the produce of the same spider. In Mr Rolt's experiment, the silk was obtained directly from the spinnerets of the animal, and not from its egg-bags or cocoons. He connected a small reel with the steam-engine of the factory in which he was occupied, and putting it in motion, at the rate of 150 feet per minute, found that a fullgrown spider would thus continue to afford an unbroken thread during from three to five minutes. The specimen of this silk which Mr Rolt presented to the Society was wound off from twenty-four spiders in two hours. Its length was estimated at 18,000 feet, its colour was white, and its lustre of metallic brilliancy, owing probably to its great opacity. Mr Rolt did not attempt to combine two or more filaments into one winding, nor to form it into thread by throwing. The thread of the garden-spider is so much finer than that of the silk-worm, that the united strength of five of the former is, according to Mr Rolt, equal only to one of the latter ; and assuming that the weight is in proportion to the strength, and that a spider will yield twice a year a thread 750 feet in length, while that produced by a single silk-worm is 1900 feet, it follows that the produce of one silkworm is equal to that of 6} spiders. “Now,' says the Report in the Society's Transactions, “as on an average it takes 3500 silk-worms to produce a pound of silk, it would take about 22,000 spiders to produce an equal quantity. Besides, spiders are not so easily confined as silk-worms, and whenever two come in contact, a battle