Theridiidae

Theridiidae is a large family of spiders, also known as the tangle-web spiders, cobweb spiders and comb-footed spiders. Members of Theridiidae are the most common arthropods found in human dwellings throughout the world.[3] The diverse, globally distributed family includes over 2,200 species in over 100 genera[4] of three-dimensional space-web-builders. Theridiid spiders are entelegyne (have a genital plate in the female) araneomorphecribellate (use sticky capture silk instead of woolly silk) spiders that often build tangle space webs and have a comb of serrated bristles (setae) on the tarsus of the fourth leg.

The family includes some model organisms for research, for example, the genus Latrodectus, the medically important widow spiders. In addition to studies characterizing their venom and its clinical manifestation, widow spiders are broadly used in research on spider silk, and on sexual biology including sexual cannibalism.

Anelosimus spiders are also model organisms, used for the study of sociality, its evolution, and its ecological and evolutionary causes and consequences. They are particularly important for such studies as the genus contains species varying from solitary to permanently social, and because sociality has evolved frequently within the genus allowing comparative studies across species. These spiders are also a promising model for the study of inbreeding as their mating system co-varies with sociality, and all permanently social species are highly inbred.

One species in Theridion, the Hawaiian T. grallator, is used as a model to understand the selective forces and the genetic basis of colour polymorphism within species. Theridion grallator is known as the "happyface" spider, as certain morphs have a pattern uncannily resembling a smiley face or a grinning clown face on their yellow body.

The family also contains the well studied kleptoparasitic species of the subfamily Argyrodinae (including Argyrodes, Faiditus, and Neospintharus) which often have triangular bodies. These spiders live in the webs of larger spiders and pilfer small prey caught by their host's web, eat prey killed by the host spider, and may consume silk from the host web, as well as attack and eat the host itself.

The largest genus with over 600 species currently placed in it is Theridion, but it is not monophyletic. Another large genus is Parasteatoda, previously Achaearanea, which includes the North American common house spider.

Many theridiids trap ants and other ground dwelling insects by means of elastic sticky silk trap lines leading to the soil surface. Despite their name, cobweb or tangle-web spiders have a huge range of web architectures.