[94] There is a nest exhibited in the Museum collection at the Jardin des Plantes at Paris, marked "Amérique du Sud," which is perhaps of this type.
That is to say, will the type of nest remain the same while the occupants vary, as in the cork nests?
If, on the other hand, we learn that these three types, the single-door wafer, the branched and unbranched double-door nests, are very local, we shall be led to inquire into the probable causes of this limitation.
But we must study much more closely the habits of these trap-door spiders, and the difficulties and dangers to which they are exposed, if we wish to appreciate fully the true meaning and intention of the structure of their nests, and to find the clue to the difficult question why one type should be more frequently adopted than another. Above all, we must discover what are their enemies, and how and when they are most exposed to them. M. de Walckenaer gives an entertaining account[95] of the enemies to which spiders generally are exposed, and of this the following list is an abstract.
[95] Histoire des Insectes Aptères (Suites à Buffon), vol. i. p. 172-7.
Many kinds of monkeys, squirrels, and several sorts of birds, as well as lizards, tortoises, frogs, and toads prey upon spiders. A species of black sheep, found in the steppes of Asiatic Russia, unearths the tarantulas (Lycosa), and eats them. ("Une espèce de brebis noire, dans les steppes de la Russie asiatique, déterre les tarentules et les mange"). In the East India Archipelago there is an entire genus of birds of the passerine order, which have been named "Arachnoptères" because the different species of which it is composed live exclusively on spiders. Besides these, the centipede (Scolopendra), and the following Hymenopterous insects, Philanthes, Sphex, Pompilus, Pimpla Ovivora, and P. Arachnitor [which last lay their eggs in the eggs of spiders], carry on perpetual hostilities against them.
I have seen it stated that ants are among the worst enemies of spiders, driving their galleries through the silk tubes of the latter and devouring their eggs. Of this I have never seen any trace, and, on the contrary, have on four occasions found the remains of ants' bodies at the bottom of the trap-door spiders' nests.
I have but seldom detected any refuse in these nests, and this accords with what M. Erber tells us[96] of the care with which Cteniza Ariana, which he watched by moonlight in the island of Tinos, carried away the empty bodies of the beetles, the juices of which had been sucked out, to a distance of some feet from its hole. In October, 1872, however, I found a black layer of débris at the bottom of five nests of Nemesia Eleanora, and this was composed principally of the remains of insects, and among others of some rather large beetles.
[96] A translation of these very interesting observations will be found below in [Appendix B].
As far as I am aware, M. Erber is the only naturalist who has ever placed any detailed observations on record as to the nocturnal habits of a trap-door spider in its native haunts; and we may learn from him how we should watch these creatures, if we wish to discover the manner in which they take their prey, and of what their prey consists.