Theridiidae
Theridiidae, also known as the tangle-web spiders, cobweb spiders and comb-footed spiders, is a large family of araneomorph spiders first described by Carl Jakob Sundevall in 1833. This diverse, globally distributed family includes over 3,000 species in 124 genera, and is the most common arthropod found in human dwellings throughout the world. Theridiid spiders are both entelegyne, meaning that the females have a genital plate, and ecribellate, meaning that they spin sticky capture silk instead of woolly silk. They have a comb of serrated bristles (setae) on the tarsus of the fourth leg. The family includes some  model organisms for research, including the medically important widow spiders. They are important to studies characterizing their venom and its clinical manifestation, but widow spiders are also used in research on spider silk and sexual biology, including sexual cannibalism. "Anelosimus" are also model organisms, used for the study of sociality, because it has evolved frequently within the genus, allowing comparative studies across species, and because it contains species varying from solitary to permanently social. These spiders are also a promising model for the study of inbreeding because all permanently social species are highly inbred. The Hawaiian "Theridion grallator" is used  as a model to understand the selective forces and the genetic basis of color polymorphism within species. "T. grallator" is known as the "happyface" spider, as certain morphs have a pattern resembling a smiley face or a grinning clown face on their yellow body. Webs. They often build tangle space webs, hence the common name, but Theridiidae has a large diversity of spider web forms. Many trap ants and other ground dwelling insects using elastic, sticky silk trap lines leading to the soil surface. Webs remain in place for extended periods and are expanded and repaired, but no regular pattern  of web replacement has been observed. The well studied kleptoparasitic members of Argyrodinae ("Argyrodes", "Faiditus", and "Neospintharus") live in the webs of larger spiders and pilfer small prey caught by their host's web. They eat prey killed by the host spider, consume silk from the host web, and sometimes attack and eat the host itself. Theridiid gumfoot-webs consist of frame lines that anchor them to surroundings and of support threads, which possess viscid silk. These can either have a central retreat ("Achaearanea"-type) or a peripheral retreat ("Latrodectus"-type). Building gum-foot lines is a unique, stereotyped behaviour, and is  likely homologous for Theridiidae and its sister family Nesticidae. Among webs without gumfooted lines, some contain viscid silk ("Theridion"-type) and some that are sheet-like, which do not contain viscid silk ("Coleosoma"-type). However, there are many undescribed web forms. Genera. The largest genus is "Theridion" with over 600 species, but it is not monophyletic. "Parasteatoda", previously "Achaearanea", is another large genus that includes the North American common house spider. , the World Spider Catalog accepts the following genera: About 35 extinct genera have also been placed in the family. The oldest known stem-group member of the family is "Cretotheridion" from  the Cenomanian aged Burmese amber of Myanmar.