Steatoda borealis

Steatoda borealis, a spider species that belongs to the genus Steatoda is one of the members family of Theridiidae. In United States, they are found east of the Rocky Mountains as well as in Alaska.

Many spiders in the genus Steatoda are frequently misidentified as widow spiders and are dubbed “false black widows”. And even though they are relatives of the widows (Latrodectus sp.), they are not medically significant spiders. Some Steatoda species will even prey on widows as well as other spiders that are considered dangerous to humans.

Quick Overview: Steatoda borealis
Medically significant: No
Body size: 1/3″ (7 mm)
Main colors: Black, Brown, White
Range: Mostly Northeastern United States and Alaska
Web: Cobweb

Steatoda Borealis Description

Steatoda borealis is a relatively dark spider with a large bulbous abdomen. The main body color ranges from dark black to brown or reddish-brown. The front and hind leg pairs are longer than the middle pairs. Since most spiders in the genus Steatoda have a similar appearance, it can be hard to make an exact ID on a species level.

Steatoda borealis in United States

In order to identify a Steatoda borealis, look for the “T” shaped mark at the front end. The underside of the abdomen is also significantly lighter than the top. However, even that mark can be faded in older specimen and is also present on many Steatoda bipunctada who occur in a similar range.

Size

Steatoda borealis grows to an average body length of 1/3″ (7 mm). Males are smaller than females.

Web

Like other Theridiidae families, these spiders also construct a cobweb with irregular tangles of sticky silken fibers. Also, these spiders have very poor eyesight and they depend on vibrations reaching them through their webs.

Steatoda borealis bite

These spiders are not aggressive, and the majority of bites to humans are caused by defensive bites delivered when a spider is unintentionally squeezed or pinched in some way. Some bites may occur if a spider misidentifies a finger thrust into its web as its normal prey, but normally, any large creature will cause these spiders to flee.

A bite will usually cause symptoms comparable to a bee sting, with symptoms ranging from local swelling to redness and some pain.

Steatoda borealis Scientific Classification

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

Distribution of Steatoda borealis in the USA

Steatoda Borealis was originally found exclusive in the Northern United States and Canada, east of the Rocky Mountains. Over the last decades, it has also spread to the south as far as South Carolina and Tennessee and is also found in Alaska.

Namely, it can be found in the following states with most occurrences in the northern states:

Steatoda borealis

4 thoughts on “Steatoda borealis

  1. Was laying in bed and about to fall asleep and noticed this guy crawling next to my head. In the southern part of Idaho. Was found inside my bedroom. My room is cold from my AC unit. Didnt bite or anything but scared the heck out of me. Body probably about the size of a dime. Maybe a little smaller

    1. Hello Rebecca, thanks for getting in touch! This is a cobweb spider of the genus Steatoda. They are also called false widow spiders and are close relatives to black widows – but not medically significant for humans or pets.
      There are several species with a similar appearance but I would say this is Steatoda borealis.

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