The tangle-web spiders or comb-footed spiders (family Theridiidae) are a large group (over 2000 species in nearly 80 genera) of haphazard web-builders found throughout the world. The characteristics of this family of spiders are that they are entelegyne (have a genital plate in the female) araneomorph ecribellate (use sticky capture silk instead of wooly silk) spiders that build tangle space webs and have a comb of serrated bristles (setae) on the tarsus of the forth leg. The family includes the genus Latrodectus the notorious widow spiders. In the United States there are five widow spiders: the southern black widow spider (Latrodectus mactans), the northern black widow (Latrodectus variolus), the western black widow (Latrodectus hesperus), the red widow (Latrodectus bishopi), and the brown widow (Latrodectus geometricus). Other species include the red-backed spider (Latrodectus hasselti) from Australia and accidentally introduced to Japan, the katipo (Latrodectus katipo) of New Zealand and the European black widow (Latrodectus tredecimguttatus) of Eurasia, among others. All have strong neurotoxic venom.
The family also contains the strange clyptoparasitic species of Argyrodes , which often have triangular or worm-like bodies. These strange creatures live in the webs of larger spiders and eat prey caught by their host's web. They sometimes attack and eat the host.
Many species of the nominate genus Theridion are known, as well as Achaearanea , the genus that includes the common house spider. At least some members of the genus Steatoda trap ants and other ground dwelling insects by means of elastic sticky silk trap lines leading to the soil surface.
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