1902 Encyclopedia > Arachnida > Arachnida - Order VII: Araneidea - General Remarks

Arachnida
(Part 29)



(29) ARACHNIDA - ORDER VII: ARANEIDEA - GENERAL REMARKS

GENERAL REMARKS. - Spiders are to be found more or less abundantly in every part of the world and in almost every conceivable position; even subterranean caves, such as those of Adelsberg and the island of Lesina, are tenanted by species peculiarly adapted by the absence of eyes to their dark and gloomy abodes. Less repulsive and forbidding in appearance than most others of the Arachnida, the Araneidea are often extremely interesting in their habits. Being almost exclusively feeders on the insect tribes, they are consequently endowed with proportionate craftiness and skill; this is shown remarkably in the construction of their snares and dwellings. The "trapdoor spider" has always been one of note in popular works on spiders' habits, and certainly the details of several different types of the trapdoor tubular nest, with the habits of the several species to which they belong, lately published by Mr Traherne Moggridge, are of the greatest interest and importance. The typical trapdoor nest is a cylindrical hole in the earth excavated by the spider itself, lined with silk and closed by a lid, which fits like a valve or cork into the opening at the surface and opening by a strong elastic silken hinge, the spring of which closes it again with some slight force. Many spiders, however, live a vagabond life, and capture their prey without the aid of a snare, by springing on it unawares, or, in some cases, running it fairly down in open view; yet craft and skill are equally apparent, whatever be their mode of life and subsistence.

To say that spiders are less repulsive and forbidding in appearance than other Arachnids, is to do them but scanty justice, for numbers of species of various genera-notably among the Salticides, or jumping spiders-are unsurpassed by insects of any order, in respect both to brilliancy of colouring and the design formed by distribution. Some of the curious and delicate little species of the genera. Argyrodes and Atiamnes are perfect marvels of metallic brilliancy and beauty. These little spiders are found living as quasi parasites, in the outskirts of the webs of the larger exotic epeirids, and appear to live on the smaller insects caught in them; probably also spinning irregular snares of their own among the lines of the larger snare. In external appearance the young of spiders do not differ greatly from the adults, except in being generally more distinct in colour and markings; in some species the characteristic markings can seldom be well traced except in immature examples. The cocoons or nests in which some spiders deposit their eggs are very beautiful, as well as varied and characteristic in form; that of Ero variegata (Bl.), a little spider not uncommon in England, would arrest the attention of even an indifferent person; it is of an elegant pear shape, formed of a strong yellow-brown silk network, and attached by a long elastic stem, of the same material, to stalks of dead grass, stick, or other substances, in shady places. Another, made by a larger spider. Agroceca brunnea (Bl.), is of a truncated pear shape, formed of a continuous white silk fabric, and attached to blades and stalks of living grass and rushes, by a short pedicle; it must, however, be seen 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 (Templ.) contain 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 temperature 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 diceros (Cambr.), found in England, is but 1/25 of an inch in length. Tropical 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 1/12th to 1/20th of an inch in length.





Spiders, besides being skillful and crafty, are very cleanly; one of our common Saltici, Epiblema histrionica (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 purpose. 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 show 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 apparently convinced of the hopelessness of retaining it. A pretty little spider, 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, amd 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 spides, 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 Proceedings Zool. 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 fulfill the office of impregnating the female. The male, nearly always the smallest, is in the case of some eperids and Thomisids not 1/110th11 or even 1/15th of the length of the female, and sometimes not more than 1/1300th part of her weight, and less than 1/1500th part of her volume 9A.W.M. Van Hasselt, Arch. Neerland, tom. 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.H., 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 nourishment 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.





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