Page:Encyclopædia Britannica, Ninth Edition, v. 2.djvu/318

Rh 298 AKACHNIDA [SPIDERS. soon after it is made, for the maker, as if prescient of the attraction of such a beautiful little object, hastens to daub it over thickly with a coat of mud or clay, which completely conceals its structure and beauty. Spiders vary greatly in their relative fertility; probably many species are rare owing to a limited fecundity. The egg sac of Agroeca brunnea (Bl.) contains about forty or fifty eggs, that of Xysticus claveatus (Walck.) about twenty, that of Ero variegata (Bl.) not so many, while that of Oonops pulcher (Tempi.) contains usually no more than two. Some spiders, however, perhaps most, construct more than one cocoon. From their mode of life spiders attain (as we should naturally suppose) their largest size, and are found in their greatest profusion, in the tropical regions ; while in more temperate climates, where the members of the insect tribes are smaller and their species fewer, we find spiders in general of comparatively smaller dimensions and less numerous in species. One of the largest known spiders, Eurypelma Klugii (Koch), Fam. Theraphosides found in Brazil, measures upwards of two and a half inches in length, with legs nine inches and upwards in span ; while the smallest known spider, Walckenaera dicer os (Cambr.), found in England, is but ^th of an inch in length. Tropi cal countries, however, although some of their spiders are giants, have numbers of small size. Numerous species have been procured from Ceylon measuring no more than from -j^th to ^ih of an inch in length. Spiders, besides being skilful and crafty, are very cleanly ; one of our common Saltici, Epiblema Jiistrionica (Koch), may often be seen brushing and cleaning its forehead and eyes with its hairy palpi, as a cat uses its paws for a similar pur pose. Probably most spiders, like the Crustacea, have the faculty of reproducing a lost limb. Instances of this are numerous (see Mr Blackwall s experiments, Report of British Association before cited), but a reproduced limb is seldom or never equal to the original one in size; this accounts for the frequency of examples captured with one or more legs, or a palpus, of dwarfed and stunted dimensions. Many spiders shew great attachment to their eggs and young. The female Lycosa will seize her egg sac again and again if it be taken from her, only relinquishing it at last when appar ently convinced of the hopelessness of retaining it. A pretty little spicier, not rare among weeds and garden plants, Theridion carolinum (Walck.), carries its egg cocoon within its legs, and searches for it anxiously if compelled to drop it. Many also of the genus Clubiona, as well as others, brood over their eggs and tend upon their young until they disperse to find their own means of subsistence. The food of very young spiders is probably wholly derived from the moisture of the atmosphere. Spiders are great drinkers, and suffer severely from drought. Mr Blackwall relates that an emaciated, half-dead example of Micaria nitens (Bl.) grew immediately plump and strong after a draught of water. In speaking of the better qualities of spiders, their attachment to their young, and the frequent fondness for each other evidenced by the apparently happy life of the male and female of some species in the same web, we must not overlook the other side of the picture. It has been well authenticated that in some species of Epeirides the female will seize and devour the male even immediately after the exercise of his natural office, which indeed he has to undertake with great circumspection and care to be able to accomplish at all. From this propensity of the female, we may account for the gradual lessening in size of some male spiders in comparison with that of the females, by a kind of sexual selection, since it is obvious that the smaller the male the better his chance of escape (see O. P. Cambridge in Zoologist, 1868, p. 216, and in Pro ceedings Zool. Soc. Lond., 1871, p. 621, and also Vinson s Spiders of Bourbon and Mauritius), and thus selection would operate until the males became so small as only just to be able to fulfil the office of impregnating the female. The male, nearly always the smallest, is in the case of some epeirids and Thomisids not -^th or even T ^th of the length of the female, and sometimes not more than -rsV-g-th part of her weight, and less then xsVjfth part of her volume (A. W. M. Van Hasselt, Arch. Neerland, torn, viii.) As a rule, however, the difference in size between the male and female spider is not nearly so great. Spiders are unable to fly, and the mode adopted by many species, and myriads of individuals, to make up for this by sailing away on their silken lines, has been mentioned ; but lately a beautiful species of Salticides, Attus volans (Cambr.), Ann. and Mag. N. II., September 1874, found at Sydney, N.S.W., has been described and figured, with large flaps or lateral extensions of the abdominal integument, by means of which the spider can sustain itself in leaping from plant to plant ; it has power to elevate and depress these flaps at will. The voracity of spiders is well known, and the propensity above noticed of the female to devour the male is but one instance of general voracity; but though thus voracious, spiders can endure extreme fasting with impunity. A small spider enclosed in a glazed case, lived and appeared healthy for eighteen months without food ; if it had any nourish ment at all during this time, it could only have been the very slight moisture that might exude from the skin of a lately stuffed bird in the case, Zoologist, 1853, p. 3766. Other instances are also on record of fasts, almost or quite as long, and borne equally well. ENEMIES OF SPIDERS. Preying upon all the insect tribes, and occasionally upon lizards (F. Pollock, Ann. N. H., October 1872) and earth-worms (E. Simon in Ann. Soc. Ent. France, 1873, 5 se&quot;r. torn. iii. p. 114 and Zoologist, 1856, p. 5021), spiders are also themselves preyed upon by both lizards and insects. More than one species of parasitic hymenoptera tend to keep spiders within due bounds ; but little has yet been done towards working out these parasites. Three species are figured in Blackwall s Spid. Great Britain and Ireland, pi. xii. ; two of them prey upon Agroeca brunnea (BL); while the third, Pompilus sepicola (F. Smith), pierces large spiders, paralysing, but not killing them ; they are then dragged to its nest, in a hole in the earth ; eggs are laid in the spider, which retains sufficient vitality to furnish fresh food to the parasitic larvas until the time for their change to the pupa state arrives. Full grown females of Lycosa campestris (Bl.) have been found by the writer in the grasp of this powerful ichneumon. From the outskirts of a single web of Epeira opuntice (Duf.), on the shores of the Sea of Galilee, the writer collected, in April 1865, many truncated pear-shaped egg cocoons belonging to the beautiful little Argyrodes epeirce (Sim.) ; and from each of these cocoons a single hymenopterous parasite shortly issued. The egg cocoons of various epeirids in England are likewise often preyed upon by numerous minute parasites of the same order. Several species of Theridion T. simile (Koch) especially are subject to a larval parasite, often as large as the. spider itself, adhering to the outside of the abdomen. Various attempts to rear the perfect insect from this para site have hitherto failed. A wide field of great interest is open to any one who should take up the investigation of the various insect parasites of spiders, with their mode of attack and subsequent victory. Other foes, common to all the Articulata, spiders also have in abundance birds, small mammals, and reptiles. Doubtless we are indebted to such enemies for the development, through natural selection, of many spiders