Eratigena Atrica – Giant House Spider

As its name suggests, the giant house spider, Eratigena atrica, is one of the largest spiders found in Europe and the United States. The species is originally from Europe and was introduced to the Western United States over 100 years ago. It has now developed large populations in the Pacific Northwest and in the Great Lakes area. The giant house spider is the fastest spider in the world with recorded speeds of up to 1.7 ft/s (0.5 m/s).

Giant House Spider Description

The giant house spider is mainly brown with several characteristic markings. The cephalothorax (head) and the legs are a dark, reddish brown with a very dark brown oval shape on its cephalothorax.

The abdomen of the spider is relatively small and lighter, almost yellowish brown and gray, dark brown or black. The spider has a pattern on its abdomen, resembling three forward pointing arrows in a lighter color.

Juvenile eratigena atrica giant house spider
A juvenile giant house spider. Older spiders are generally darker but mostly retain the markings. Photo: Flickr

The giant house spider is often confused with the similar looking hobo spider (Eratigena agrestis) that is also common in the Pacific Northwest. The hobo spider has very similar markings but is generally smaller than the giant house spider and has shorter legs. The related grass spider (Agelenopsis sp.) is also often confused with the giant house spider. None of these species is considered dangerous for humans.

Size

While the body of the giant house spider reaches sizes comparable to other spiders, it has very long legs for a spider of its size. Male and female specimens look very similar with the female being slightly larger than the male. An adult female giant house spider can reach an average body size of 0.73 inch (18.5 mm) with an average leg span of 1.8 inches (45 mm). Some female specimens reach a leg span of over 3 inches (70 mm). The male grows to an average body size of 0.47-0.59 inches (12-15 mm)´and its average leg span is also slightly smaller than the female’s.

Eratigena atrica or duellica long legs brown size comparison with dollar
Notice the long legs of the giant house spider. Photo: Wikimedia Commons

Web

The giant house spider is part of the funnel-weaver family. It builds funnel shaped webs in corners or edges inside houses or under rocks or small caves. The web itself is not stick. The spider lurks on the edge of the web and as soon as it feels any vibrations, it races towards the potential prey animal and subdues it with a bite.

Inside houses, the funnel-webs of giant house spiders are often found in corners on the ground as well as on the ceiling or hidden behind furniture. Since they don’t like to be disturbed by humans, they are most commonly seen in basements or darker areas of houses.

Bite

The giant house spider is not a medically significant spider. As almost all spiders, it possesses venom glands and given its size, also the possibility to penetrate human skin. However, the spider itself is very shy and its first instinct is to run (very fast) and hide when a larger being (humans or animals) approaches. Therefore, bites are very rare. In the few cases in which a giant house spider bites a human or a pet, the symptoms can include some local swelling and pain, comparable to a bee sting.

Eratigena atrica giant house spier upside down long legs brown spider in Washington State
A giant house spider upside down with very long legs. Photo: Martin Cooper

Geographic Range of the giant house spider in the United States and its habitat

The giant house spider was introduced to British Columbia, Canada, around 1900 and has since spread out along the U.S. West Coast. It is a very common spider in Washington State and Oregon. Independent populations have also been recorded around the Great Lakes in Wisconsin and Michigan.

The giant house spider prefers dry habitats. It is often found under rocks and in caves in a cool and dry environment. An average female spider lives for 2-3 years with some individuals living for up to six years. During the colder winter months, the spider often seeks refuge inside people’s homes. The fact that the spider is often found in or around homes has earned it its common name.

Giant house spider Eratigena atrica found by Thalia in Washington State
A giant house spider found by Thalia in Washington State

Eratigena atrica scientific classification

  • Kingdom: Animalia
  • Phylum: Arthropoda
  • Subphylum: Chelicerata
  • Class: Arachnida
  • Order: Araneae
  • Infraorder: Araneomorphae
  • Family: Agelenidae
  • Genus: Eratigena
  • Species: Eratigena atrica

Until 2013, Eratigena atrica was classified as Tegeneria atrica. Some scholars also distinguish among three species of the giant house spider: Eratigena duellica, Eratigena saeva and Eratigena atrica. This overview considers only one species, Eratigena atrica.

References

  • Taxon details: World Spider Catalogue
  • Binomial name from: Koch, 1843
  • https://www.naturespot.org.uk/species/giant-house-spider
  • Oxford, Geoff S; Bolzern, Angelo (2018). “Molecules v. Morphology—is Eratigena atrica (Araneae: Agelenidae) One Species or Three?”. Arachnology17 (7): 337–357. 
Eratigena Atrica – Giant House Spider

3 thoughts on “Eratigena Atrica – Giant House Spider

  1. Found this guy in my bathroom tonight, a little bit larger than a quarter. I live in Yakima, Washington.

    1. Hello Mary, thanks for getting in touch! This is some type of funnel-weaver spider of the spider family Agelenidae. It could be a giant house spider (Eratigena atrica): https://usaspiders.com/eratigena-atrica-giant-house-spider/ or also a hobo spider (Eratigena agrestis): https://usaspiders.com/eratigena-agrestis-hobo-spider/
      I am leaning towards giant house spider.
      Despite the hobo spider’s bad reputation, both species are not medically significant and there is no proof that they can cause any harm to humans or pets.

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