Trap-door nests are made by spiders belonging to two widely different groups, namely the Lycosidae or wolf-spiders, to which the true tarantula belongs, and the Mygalomorphae, containing the species which construct the best-known types of this style of burrow.
In the trap-door species of Lycosidae, like, for instance, Lycosa opifex of the Russian steppes, the hinge is weak and the lid of the burrow is kept normally shut by being very much thicker and heavier at its free margin opposite the hinge so that it readily falls by its own weight.
Be that as it may, the snare in many instances, as in that of the Agalenidae (Tegenaria, Agalena), a family closely allied to the Lycosidae, is a horizontal sheet of webbing, upon which the spider runs, continuous with the lower half of the aperture of the tube, of which it is simply an extension.
Examples of Selenops (Clubionidae) lie flat and absolutely still on the bark of trees, to which their coloration assimilates, and spring like a flash of light upon any insect that touches their legs; the Lycosidae dart swiftly upon their prey; and the Salticidae, which compared with other spiders have keen powers of vision, stealthily stalk it to within leaping distance, then, gathering their legs together, cover the intervening space with a spring and with unerring aim seize it and bury their fangs in its body.
Other species of wandering habits carry the cocoon about with them, sometimes attached to the spinnerets, as in the Lycosidae, sometimes tucked under the thorax, as in the large tropical house-spider, Heteropoda regia, one of the Clubionidae.
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