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Triangulate Household Spider: A Common Harmless Spider
Barb Ogg, Ph.D., Extension Educator
The triangulate household spider, Steatoda triangulosa, is a very common house spider and one many homeowners see hanging in irregular webs in dark corners of houses, basements, garages and outbuildings. It is quite small–the body is only about 1/8- to 1/4-inch long. The cephalothorax (located behind the spiders' head) is brownish orange. The center of its brown abdomen has several distinctive white and yellow triangular spots, which explains its common name. Its legs are light yellow, with slightly darker rings at the ends of the joints.
UPDATE July 16, 2008. Recently, the our office has had a number of phone calls from people asking if this is a dangerous spider. This is a very common spider and it is not considered to be a spider of medical importance.
This species is probably native to Eurasia and was probably introduced to the U.S. in the early days of colonization. It is found throughout the U.S. and is a very common spider found in Nebraska.
The triangulate household spider belongs to the family of comb-footed spiders, Theridiidae. Like other members of this group, these spiders build irregular webs. It takes anywhere from several nights to more than a week for these nocturnal spiders to finish their web.
The spider hangs upside down while waiting for unsuspecting prey to fly or fall into sticky places on the web. Using a comb of serrated bristles on their hind legs the spider covers its prey in silk and waits for it to stop moving before biting. The triangulate household spider has been found to prey on many kinds of arthropods, including ants, spiders (including the brown recluse), ticks and pillbugs.
This spider's cobwebs may also be found outdoors, especially in areas where night-flying insects are attracted to lights from windows or porch lights.
This spider mates and produces egg sacs from late spring through early fall. An egg sac is about the size of the adult spider and is made of loosely woven white silk. About 30 eggs can be seen in each sac.
Recently, we have had a number of phone calls asking about the seriousness of this very common spider. There have been no known cases of human envenomation by S. triangulosa. Experts don't consider it to be a medically important spider.
Control: No extraordinary measures are needed to control this spider. The low-toxic method of dealing with web-building spiders is to knock down the webs and step on the spider or use a vacuum cleaner to remove both spider and web.
For more information about spiders and their control, visit HERE
The information on this Web site is valid for residents of southeastern Nebraska. It may or may not apply in your area. If you live outside southeastern Nebraska, visit your local Extension office
Photo credit: Cobweb Weaver, Steatoda triangulosa - University of Nebraska-Lincoln Department of Entomology, http://entomology.unl.edu.