Certain nests which were furnished with two doors of the cork type were observed by Mr. S. S. Saunders[82] in the Ionian Islands. The door at the surface of these nests was normal in position and structure, but the lower one was placed at the very bottom of the nest and inverted, so that, though apparently intended to open downwards, it was permanently closed by the surrounding earth. The presence of a carefully constructed door in a situation which forbade the possibility of its ever being opened seemed, indeed, something difficult to account for. However, it occurred to Mr. Saunders that, as these nests were found in the cultivated ground round the roots of olive-trees, they may occasionally have got turned topsy-turvy when the soil was broken up. The spider then, finding her door buried below in the ground and the bottom of the tube at the surface, would have either to seek new quarters or to adapt the nest to its altered position, and make an opening and door at the exposed end. In order to try whether one of these spiders would do this Mr. Saunders placed a nest, with its occupant inside, upside down in a flower-pot. After the lapse of ten days a new door was made, exactly as he had conjectured it would be, and the nest presented two doors like those which he had found at first.
[82] Description of a species of Mygale from Ionia in Trans. of Ent. Soc. (London, 1839), III. p. 160.
There is a specimen of one of these inverted nests, with its two doors, in the British Museum, and this might easily be supposed, at first sight, to be an example of a new kind of double-door nest. On close inspection, however, it will be seen that one of the two doors is discoloured and partly decayed, this being, no doubt, the one which had been buried beneath in the earth and so rendered useless.
Questions have often been asked as to the manner in which trap-door nests are commenced in the first instance, and whether the weaving of the silk lining is begun at the top or the bottom of the tube.
The structure of the cork door also, which often appears so perfectly turned as to resemble the work of a potter's lathe, is another difficulty.
These questions have, as it seems to me, been needlessly complicated by taking it for granted that the perfect nest of the mature spider is made all at one time, that the tube, perhaps of a foot in length, is excavated, lined, and furnished with a door within some short period of time, such as ten days or a fortnight, perhaps.
On the contrary, I believe that the nests are, as a rule, the result of many successive enlargements, and that the nest of the infant, the tube of which is no bigger than a crowquill, is not abandoned, but becomes that of the full-grown spider. This must require time, but how long, whether months or years, we have yet to learn.
Very little is known at present as to the longevity of spiders, but Mr. Blackwall[83] says that some live only one year, while others, such as Tegenaria civilis and Segestria senoculata, have been known to live four.
[83] Spiders of Great Britain and Ireland, p. 8.
Whether the trap-door spiders are very long lived or not I cannot positively say, but, from the appearance of the growth of moss and lichen on the doors of some nests which I have observed, I am inclined to think that they must have been inhabited for more than a twelvemonth.