Steatoda Grossa – False Black Widow Spider

The Steatoda grossa, commonly called the false black widow spider or cupboard spider can be found throughout the United States. It is from the family of Theridiidae, the same as the black widow spiders. They build similar webs and have a similar body shape and color as black widows. Hence, their common name false widow. The bite of a false black widow spider is considerably less severe than a real widow’s bite. However, it is one of the few species that are considered medically significant as the bite can cause severe pain. It is from the same genus as the Steatoda triangulosa and the Steatoda bipunctada.

Steatoda grossa is an imported species that originated in Europe. In the United States, it occurs most often along the East Coast as well as in California. But over the last years, it has spread throughout the United States and can be found in every state.

False Black Widow Spider Description

Steatoda grossa has a similar body shape as the real widow spiders of the genus Latrodectus. The abdomen of the female is large, bulbous and round. Their body color ranges from light brown to purplish to deep black. Especially older female specimen are often confused with black widows. If you can catch a glimpse at the underside of the abdomen and you cannot see a red hourglass shape, it is not a real black widow and you are most likely dealing with a false widow. If the general color of the body is more like a dark purple instead of black, it is also an indication for a false widow.

Size

The female false black widow normally has a body size of 0.25-0.40 inches (6-10 mm). Their total leg span is about 1 inch (25 mm). The male is slightly smaller and has an oblong abdomen.

Web

Steatoda spiders are part of the cobweb spider family. They don’t spin beautiful round webs like orb weavers in the open. Their webs are tangled and irregular with unorganized strands of sticky silk. They often build their webs in corners of buildings or other crevasses and spend most of their time inside their web waiting for prey to get tangled up in it. This has also earned them their other common name Cupboard Spider.

Interestingly enough, one of the preferred prey are real black widow spiders as well as other small creatures.

False Widow Bite

The Steatoda grossa is, like the other species from its genera, a timid spider. Whenever a human or a large animal gets close to their web, they will be able to feel the vibrations and hide away from the danger. They only bite if they feel immediately attacked or trapped. Never touch a cobweb in a corner with your hands, use a broom or another tool to avoid being bitten in the hand.

The bite of a false widow is considered medically significant. That means that the bite itself can be painful and cause blistering in the area around the bite. In addition, the bite may lead to a general discomfort and even fever for several days. The bite does not cause any long-term effects and is not as severe as the bite of a real black widow.

Scientific Classification of Steatoda grossa

• Kingdom: Animalia
• Phylum: Arthropoda
• Subphylum: Chelicerata
• Class: Arachnida
• Order: Araneae
• Infraorder: Araneomorphae
• Family: Theridiidae
• Genus: Steatoda
• Species: Steatoda grossa

Other common names

Steatoda grossa is known under the following common names: False widow spider, false black widow spider, cupboard spider, brown house spider and dark comb-footed spider.

False Widow Spider Range in the USA

The Steatoda grossa can be found throughout the United States in the following states: Alabama, Alaska, Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Florida, Georgia, Hawaii, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, Montana, Nebraska, Nevada, New Hampshire, New Jersey, New Mexico, New York, North Carolina, North Dakota, Ohio, Oklahoma, Oregon, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Utah, Vermont, Virginia, Washington, West Virginia, Wisconsin, Wyoming