That most of the vagabond spiders can see well within the range of several inches there is no doubt, though some observers have been misled by the result of certain experiments on the Lycosidae, or “Wolf-spiders.” It will be remembered that the female Lycosid carries her egg-bag about with her, attached usually to her spinnerets. If it be removed and placed close at hand, the spider experiences the greatest difficulty in finding it again. Lubbock attributed this to defective sight, whereas it merely arises from unfamiliarity with the appearance of the egg-bag, which, since its construction, has been so situated as to be out of the view of the spider. Peckham found that spiders of the genus Theridion, accustomed to the sight of their cocoons, readily recognised them by that sense when removed to a distance.
The most keen-sighted of the spider tribe are undoubtedly the Attidae, or Leaping-spiders. The little black and white striped Wall-spider, Salticus scenicus, is probably a familiar object to most of our readers, and a very little observation of its movements, like those of a cat stalking a bird, will convince the observer that its visual powers are wonderfully keen and accurate. Its attitude of “attention” on sighting its prey, its stealthy manœuvring to approach it unobserved, and the unerring certainty of its final leap, are very interesting to witness.
It is somewhat noticeable that both in the Epeiridae and in the Attidae the two portions of the body, cephalothorax and abdomen, have more than the usual freedom of independent motion. In the Orb-weavers this gives play to the spinnerets in binding up a captured insect, but in the Leaping-spiders it allows of the rapid directing of the large anterior eyes towards the quarry, as it continually alters its position.
Professor and Mrs. Peckham of Wisconsin[[300]] performed some interesting experiments to ascertain the sensitiveness of the spider’s eye to colour. Freely communicating compartments of differently coloured glass were constructed, and spiders were confined in them, when it was found that red was the most and blue the least attractive hue. This agrees well with what Lubbock found to be the case with ants, but those insects displayed a greater antipathy for blue and not so marked a preference for red.
Hearing.—Most of our knowledge about the auditory sense of spiders is due to experiments performed by C. V. Boys,[[301]] and repeated by Professor and Mrs. Peckham.
The spider usually responds to the stimulus in one of two ways; it either raises its front legs, extending them in the direction of the sound, or it allows itself to drop suddenly, as though in alarm. It was only in the case of the Epeiridae that any results were obtained, and these spiders were more sensitive to low than to high notes. Now, as M‘Cook points out, it is exceedingly strange that the nomadic and hunting spiders, to which the sense of hearing might be expected to be extremely useful, should be deficient in this faculty, while the sedentary spiders, to which it would appear comparatively unimportant, should possess it in a tolerably developed form. That writer may possibly be correct in supposing that the sense, as possessed by spiders, is hardly differentiated from that of ordinary touch, and that the web-making species are only aware of sounds by the vibrations communicated to their feet by the medium of the web. However this may be, we must reluctantly but sternly reject the numerous and seemingly authentic stories, often connected with historic personages, which credit the spider with a cultivated taste for music.
We have seen that among the spiders which possess a stridulating apparatus it is confined, in certain groups, to the male, or if present in the female it exists only in a rudimentary form. If in these cases stridulation has been rightly interpreted as a sexual call, the power of hearing, at least in the female, is of course connoted. The spiders in question are members of the Theridiidae, a family closely allied to the Epeiridae, and therefore more likely than most groups to possess the power of hearing.
Theraphosid spiders show no response to the stimulus of sound, and among them stridulation is not confined to one sex. If, as is generally believed, the organ is used to warn off enemies, it is not necessary that the sound produced should be audible to the spider itself. If there be any true hearing organ in spiders its location is quite uncertain. Some have supposed the so-called lyriform organs in the legs to have an auditory function, while others have supposed the power of hearing to reside in certain hairs, of which there are several different types distributed over the body and limbs of the animal.
Spider Intelligence.—The experiments performed by the Peckhams clearly proved that spiders have short memories—a sure indication of a low state of intelligence. Members of the Lycosid or “Wolf-spider” group, when deprived of their cocoons, recognised them again after a few hours, but in most instances they refused to resume them after a lapse of twenty-four hours, and in every case an absence of two days sufficed to prevent any sign of recognition on their restoration. Moreover, when, after a shorter interval, the cocoons of other spiders, even of different genera, were offered to them, they appeared equally satisfied, and attached them in the orthodox manner, beneath the abdomen. The same treatment was even accorded to pith balls, which, if of the right size, seemed to be a perfectly satisfactory substitute. The contents of one cocoon were replaced by a shot three or four times their weight, but the spider accepted it with alacrity, spending half an hour in refixing it, when its weight caused it to fall from its attachment.
The habit of “feigning death,” which seems to be especially characteristic of the Epeiridae or orb-weaving spiders, probably arises from no desire to deceive its adversary as to its condition, but from an instinct to remain motionless, and therefore inconspicuous. Where a nomadic spider seeks safety in flight, a sedentary species finds a greater chance of escape in dropping a certain distance, and, while still attached by its silken line, giving as little evidence of its whereabouts as possible—trusting, in many cases, to its protective colouring. This method, moreover, has the advantage of facilitating its return to the web when the danger is past—a feat of which it would be quite incapable were it once to relinquish its clue.