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The spider family Theridiidae (cobweb weavers or combfooted spiders) has a worldwide distribution and includes 2387 described species, ranking it among the few most species-rich spider families (Platnick 2014). According to Levi (2005), 234 theridiid species are known from North America north of Mexico. One of these species, the Common House Spider (Parasteatoda tepidariorum) may be the most common spider in the world, living in abundance in association with humans on every continent except Antarctica, occurring both indoors and outdoors (Bradley 2013).
Theridiids are sedentary and typically construct an irregular web with sticky strands attached to the substrate. The strands break when prey touches the line, pulling the prey toward the center of the web. The web is usually built beneath some sort of cover, such as a rock face, a branch, or even a single leaf. Some theridiids build webs consisting of just a few lines of silk. Members of some theridiid genera (Rhomphaea, Argyrodes) are found in the webs of other spiders, especially orb weavers, and may feed on their hosts, their host's eggs, or their host's prey. Other "atypical" feeding habits are knowns as well. For example, Dipoena and Euryopis are ground-dwelling ant predators. Latrodectus (the "widow" spiders) are well known for being venomous to humans, although they will choose to retreat rather than bite if given the option. (Levi 2005; Bradley 2013)
Theridiids typically have a rounded abdomen tapering to a point at the spinnerets. This shape gives the abdomen a characteristic teardrop shape when the spider is hanging upsidedown in its web. Some theridiids hang a leaf or other debris in the web and rest beneath this cover. Many theridiids are conspicuous and colorful. Like most spiders, theridiids have eight eyes. The fourth tibiae of most theridiids sport curved serrated bristles which the spider uses to draw out and fling sticky silk during a wrapping attack. (Levi 2005; Bradley 2013)
Levi (2005) reviews key aspects of the taxonomic history of the Theridiidae and provides some key references.