TRAP-DOOR SPIDERS, large hairy theraphosid spiders of the family Ctenizidce and its allies, which inhabit dry warm countries and form well-like pits or burrows in the ground, closed by a hinged lid. These burrows are placed in high, well-drained situations and are dug by the owners, who cut down and carry away the earth in their jaws, depositing it at some distance. The holes vary in size with the species and age of the occupant, and the largest may be more than a foot deep. The burrow of a species (Ctenisa californica) common in southern California is of that depth, and an inch in calibre, when the owner is fully grown. In some species the wells have a branch bur row slanting from one side, and others make two entrances, so that a plan of the burrow would resemble a Y. These burrows are lined with a coating of silk, and in every case the entrance (or entrances) is closed by a tight fitting circular door composed of clay, bound and lined with silk, and hinged at one side to the lining of the burrow; the top of the door is left rough and earthy, so that when it is closed nothing betrays the presence of such a contrivance. In this snug castle the spider
dwells in safety and comfort, rearing its young under the protection of the door, which it can hold so firmly shut that nothing short of tearing the structure apart will suffice to open it. In the species of the south of Europe the lining and door are much thinner than those made by the American trap-door spiders; and if these doors are torn off a new one will be made overnight, for several nights in succession or until the insect's strength is so exhausted that it can no longer produce the requisite silk. For further facts consult general works, especially Mogg ridge, (Harvestjng Ants and Trap-door Spiders' (London 1873). See SPIDERS.