Theridiidae: Cobweb Weavers

Theridiidae: Cobweb Weavers

Achaearanea tepidariorum from Virginia
Photo by Lindsey Pyne

Theridiidae are the cobweb weavers. These shy spiders are common in and around houses and other structures, where they make irregular webs- hence the common family name. This family includes the widows (not usually found in the Midwest). Most species are harmless to humans and prefer to run rather than bite defensively.

Steatoda triangulosa is one of the most common species of spiders around the house. They prefer dark corners and often make webs behind furniture. I often find them near Pholcus phalangioides. The webs can become quite messy at times, littered with insect debris and empty egg sacs. When this happens, the webs can be gently swept or dusted. The spiders will build new webs shortly. Avoid vacuuming the webs in order to avoid accidentally vacuuming a spider.


At my old house (Minneapolis)	S. triangulosa at my current house (also in Minneapolis, MN)


This is generally a docile species	Next to finger	With prey	With egg sacs (many empty)


Typical habitats for S. triangulosa, A. tepidariorum, and P. phalangioides

Achaearanea tepidariorum is also known as the common house spider. I often encounter these in the greenhouse on the University of Minnesota St. Paul Campus, but have found them in and around houses and garages as well. They are variable in color/pattern. Females are 6 to 8 mm, males are 4 to 6 mm, and legspans are 15 to 20 mm. Eggs occur in summer and females can live for over a year.


With yellowjacket	A dark individual from the Twin Cities area, MN


Light individuals from Twin Cities		Females with egg sacs

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