Theridiidae

Theridiidae, commonly called tangle-web spiders, cobweb spiders, or comb-footed spiders, is a large family of araneomorph spiders first named by Carl Jakob Sundevall in 1833. With roughly 3,000 species across 128 genera, this diverse and worldwide family is the arthropod group most frequently encountered inside human homes. Female theridiids are entelegyne—they possess a genital plate—and the spiders are ecribellate, meaning they produce sticky capture silk rather than woolly silk. A distinctive feature is a comb of serrated bristles, or setae, on the tarsus of the fourth leg.

The family includes several model organisms for research. Medically important widow spiders are studied for their venom and its clinical effects, as well as for spider silk and sexual biology, including sexual cannibalism. Species in the genus *Anelosimus* serve as models for sociality, since social behavior has evolved repeatedly within the genus, enabling comparative studies across species that range from solitary to permanently social. These spiders also offer a promising system for studying inbreeding, as all permanently social species are highly inbred. In Hawaii, *Theridion grallator*—known as the “happyface” spider because certain morphs display a pattern resembling a smiley face or grinning clown on a yellow body—is used to understand the selective forces and genetic basis of color polymorphism.

Webs vary widely within the family, though many build tangle space webs, giving them their common name. Some trap ants and other ground-dwelling insects using elastic, sticky silk trap lines that reach the soil surface. Webs are often left in place for long periods, expanded and repaired, with no regular pattern of replacement observed. Well-studied kleptoparasites in the subfamily Argyrodinae (*Argyrodes*, *Faiditus*, and *Neospintharus*) live in the webs of larger spiders, stealing small prey caught by the host, consuming silk from the host’s web, and sometimes attacking and eating the host itself. Gumfoot-webs consist of frame lines anchoring the web to surroundings and support threads coated with viscid silk. These webs may have a central retreat (Achaearanea-type) or a peripheral retreat (Latrodectus-type). Building gumfoot lines is a unique, stereotyped behavior likely shared by Theridiidae and its sister family Nesticidae. Among webs without gumfoot lines, some contain viscid silk (Theridion-type), while others are sheet-like and lack viscid silk (Coleosoma-type). Many additional web forms remain undescribed.

The largest genus is *Theridion*, with over 600 species, though it is not monophyletic. *Parasteatoda* (formerly *Achaearanea*) is another large genus and includes the North American common house spider. As of January 2026, the family contains 138 genera and 2,619 species, along with about 35 extinct genera. The oldest known stem-group member is *Cretotheridion*, found in Cenomanian-aged Burmese amber from Myanmar.