Steatoda triangulosa, or the triangulate household spider is one of the most commonly encountered spider species within homes where they build many cobwebs that can pose a nuisance to residents. Adults of this species are relatively small at only ⅛ to ¼ of an inch in length, but their yellow legs and the white and yellow triangular markings on their brown and bulbous abdomen make them easily identifiable. Triangulate household spiders generate a high number of calls to pest control companies and university extension offices from residents asking if these spiders are dangerous. While triangulate household spiders are not considered dangerous, very rare incidents of people sustaining medically significant bites from these spiders have occured and are well documented.

Triangulate household spiders are native to Eurasia and they probably arrived in America for the first time during the early colonial era. Today, these spiders are abundant throughout the US, and they have evolved to thrive within human settings. According to an online survey of citizen scientists, triangulate household spiders have been found indoors 184 times, and they have been found outdoors only 26 times. These spiders belong to the Theridiidae family of spiders, also known as comb-footed spiders, and spiders in this family build numerous tattered webs. Triangulate household spiders hang upside down in their webs while waiting to catch winged prey, and they are known for preying on insects and arachnids that are superior in body size.

It is often said that triangulate household spiders are harmless to humans, and that no medically serious bite incidents involving this species have been documented. While this is true in the US, case reports describing medically significant bites from this species have recently been published in Colombia and France. The triangulate household spider is closely related to black widow spiders, and it belongs to the Stetadoa genus, which includes several species that have been known to inflict medically significant bites including the noble false widow. In 1983, a 49 year old Frenchman experienced neurological symptoms in response to a verified triangulate household spider bite. The man was hospitalized and showed symptoms similar to those experienced from black widow bites. Another documented incident in Colombia involved a woman who sustained a spider bite before her dog ate the spider. Both the woman and the dog exhibited several flu-like symptoms including vomiting and fever, and the spider culprit was suspected of being a Stetadoa species, most likely the triangulate household spider.

Have you ever sustained a bite from a house spider?