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.
More often it consists of a thick felting of silk, either spun in one continuous piece into a globular form, as in the Aviculariidae, or composed of two plate-like pieces, an upper and a lower, united at the edges and lenticular in shape, as in some of the Lycosidae.
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.