Parasteatoda tepidariorum, the common house spider, referred to internationally as the American house spider, is a spider species of the genus Parasteatoda that is mainly indigenous to the New World, with P. tepidariorum australis (common gray house spider) but has achieved a cosmopolitan distribution. American house spiders are synanthropic and build their tangled webs in or near human dwellings, greenhouses or similar, often in secluded areas such as between loose walls and behind open doors and attic windows. Statistically, they are the most often encountered spider by humans in North America, and least likely to adopt defensive behavior in their vicinity. Their prey mechanism is similar to that of the other cobweb spiders: the spider follows disturbances transmitted along the web to entangle and then paralyze its prey, which usually consists of household insects and other invertebrates (often considered as pests).
American house spiders are generally dull brown in coloration, with patterns of differing shades often giving a vaguely spotted appearance (particularly noticeable on the legs). Their average body size is a quarter-inch (6 mm) long, but they can be an inch (2.5 cm) or more across with legs outspread. Their size and coloration allow the spiders to blend into the background and escape notice.
Like some other species of the family Theridiidae, P. tepidariorum is similar in body shape and size to widow spiders, which have venom that is classified as potentially dangerous.
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Inspect
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American house spiders will bite humans only in self-defense, when grabbed and squeezed. Although the bite of this species is relatively less severe compared to other theridiids, it has to be considered. Bites of P. tepidariorum can cause severe pain with a median duration of 16 hours, and in some cases systemic effects; which is very similar to the symptoms of steatodism (i.e. bites of false widows in the genus Steatoda).
Steatoda and Parasteatoda species can inflict bites with similar, but far less severe, painful symptoms to those of black widows. It is also powerful enough to kill the same species of spider on occasion. The synanthropic habits of several species may play a role in cases of human biting.
As these spiders live in constant proximity to humans, they are not usually aggressive and will even let a human hand approach their web. Like any other spider, however, they are afraid of bigger foes, and, in most cases, will retreat behind an obstacle (such as a dried leaf or prey remains) upon perceiving more than usual disturbance to their web. Further disturbance may lead to the spider dropping down on a thread, then running away from the web. If the distance is not considerable, it will usually return to its web within a couple of days. Otherwise, it will start a new one.
