Spiders

by Cecil Warburton

In the autumn and spring, eggs and newly-hatched young were often found in the nests. Late in March a small hole, 1/16 inch in diameter, was noticed at the end of some of the webs, and presently the young began to emerge—never to return to the nest. They immediately climbed the highest objects at hand, and some were seen to be carried off by the breeze.

Enock found, by an ingenious experiment, that the sand which is incorporated in the aerial part of the tube—no doubt to render it inconspicuous—is obtained from within, and not from outside the nest. Carefully covering the exposed web, he powdered the ground all round it with red brick-dust, but the particles which the spider embedded in the web were of brown sand, evidently obtained from the bottom of the burrow and not from the surrounding surface. But in the case of some newly-dispersed young spiders he was able to see this operation performed. The first part of the nest to be made was the aërial portion, at the foot of which the digging was commenced. Particles of sand were brought up in the jaws of the young spider and pushed into the weft of the tube. Occasionally the jaws were thrust through the delicate web and particles from without were seized and pulled into the silken fabric.

It is sad to have to relate that such young spiders as did not emerge from the web within a reasonable time were devoured by their unnatural parent. It sometimes happened that a change of weather rendered it unsuitable for the departure of the young, and in this case the mother closed up the exit-hole, and retired to feed upon her offspring! Thus, though there were as many as a hundred and forty in a brood, a good many perished at the outset, and the ants in the surrounding soil accounted for some of the rest.

The Atypidae form a small outlying group of the Theraphosid spiders and are able to live in colder regions than most of their relatives. The great bulk of the division belong to the family Aviculariidae.

Some of the Aviculariidae are not unlike Agelena in their mode of life, spinning a dense sheet-web terminating in a tube, and entrapping their prey. Far the greater number, however, as far as their habits are known at all, are earth dwellers, either inhabiting more or less complex burrows of their own, or sheltering under stones or in chance cavities by day and emerging at night to seek food in the immediate neighbourhood of their hiding-places. Some of them are quite small, but the majority are large robust spiders, of formidable appearance. The largest known spider, Theraphosa leblondi, is found in South America, and its body measures more than three and a half inches in length. Few spiders have attracted more attention than the fabricators of the curious “trap-door” nests, which are common in the Riviera, and indeed in all the countries bordering the Mediterranean. But abundant though they are, they are extremely difficult to find, and it is generally only by chance that their existence is detected.

The Tarantula occasionally closes the mouth of her tunnel with a sheet of silk in which are encrusted the débris of insects or particles of soil. She does this at the time when she is spinning her cocoon and any intrusion is particularly inopportune, but she does it also on other occasions which are not so easily accounted for. A reason which would naturally occur to us would be the exclusion of excessive rain or excessive sunshine, but the facts, unfortunately, do not accord with this explanation.

Now, however desirable occasional closure may be, a permanent door would hamper the tarantula in her hunting operations, but the habits of the trap-door spider are different, and she closes her retreat with a wonderful hinged lid or “trap-door.” And the commonest form of trap-door is also the most perfect, being thick and tapering, and fitting accurately into the bevelled mouth of the tube like a stopper in the mouth of a bottle. It is made of alternate layers of spider silk and earth, and is free for more than half its circumference, the remaining portion of the surface disc being attached to the side of the tube by a flexible hinge of silk. Moggridge dissected the door of a full-sized tunnel into fourteen graduated discs. The smallest—and of course the lowest—represented the first door ever made by the spider, and the successively larger discs indicated the stages at which its increasing size rendered an enlargement of the tube—and therefore of the door—necessary.

The spider always interweaves vegetable matter from the neighbourhood into each new disc, so that, as a rule, it is entirely indistinguishable from its surroundings when closed; and not only dead vegetable matter, for if the tube is situated amongst moss, moss grows upon the lid. From our previous experience, however, we shall not be surprised to find that blind instinct and not forethought is responsible for this action. Moggridge removed the lid of a tunnel and also cleared the ground immediately round it of all vegetation; nevertheless, when the spider made a new door, it covered it with moss taken from the undisturbed vegetation beyond, so that the trap-door was now conspicuous as a green oasis in a sandy desert! And on another occasion a spider interwove fragments of scarlet fabric left purposely at hand into the lid of its tunnel. It is clear, therefore, that the decoration of the door is due to an instinct which impels the spider to utilise any material of the neighbourhood without any regard to the effect produced.

The tube is densely lined with silk, which affords its architect a secure foot-hold, and if any enemy attempts to open the lid from without, the spider resists with all its strength—which is not inconsiderable—clinging on to its under surface with its front legs and jaws, while the claws of its other feet grasp the silken walls of the tube.