Scotophaeus Blackwalli – Mouse Spider

Scotophaeus blackwalli, the mouse spider is a ground spider that is common in Central and Northern Europe and the Western United States. The spider is not of medical significance and should not be confused with the venomous mouse spiders found in Australia of the genus Missulena.

Description of the mouse spider

Scotophaeus Blackwalli Mouse Spider Brown and Gray Spider in Oregon and California
A Scotophaeus blackwalli mouse spider with its dark and velvety abdomen. Photo: Mike Talbot

The mouse spider is part of the Gnaphosidae ground spider family. Its abdomen is mostly gray and velvety like the fur of a mouse. The cephalothorax (head) of the spider and the legs are usually in a lighter color, either brown or gray. The body of the spider can sometimes appear shiny even though it is covered with small hairs.

Aside from their velvety gray abdomen, that reminds of a mouse, the mouse spider also has a very peculiar way to move. It can move very quickly but often stops abruptly for a short period of time and then continues the movement. This resembles the movement of mice and might have also led to the spiders common name.

Juvenile Scotophaeus Blackwalli Mouse Spider in North America brown and gray with spinnerets
A juvenile mouse spider. Adult individuals develop darker colors. Photo: Mike Higgot

The spiders is sometimes confused with the broad-faced sac spider (Trachelas tranquillus) or the woodlouse hunter (Dysdera crocata). In California, the spider can be confused with the female Metaltella simoni hacklemash weaver. The mouse spider can best be distinguished by the velvety gray abdomen and the fact that its body is almost touching the ground when moving and appears lower than the legs.

Scotophaeus Blackwalli Mouse Spider in Washington State moving
The body of the mouse spider is very close to the ground when moving. Photo: Mick Talbot

Size

Scotophaeus blackwalli is a medium-sized spider. Females reach a body size of up to 0.5 in. (12 mm) while males are slightly smaller. They reach a body size of up to 0.35 in. (9 mm).

Web

Ground spiders are hunting spiders that don’t spin webs to catch their prey. They roam around at night looking for small insects they can prey on. Mouse spiders also feed on dead insects and other spiders. They produce gluey silk with their relatively large spinnerets which the use to immobilize and subdue their prey. Thanks to this feature, they are able to prey on relatively large prey animals, including other, larger spiders.

Mouse spiders spin web-like structures to lay their eggs on which are then covered with more silk to protect the offspring. These web-like formations are often found inside homes in the Western United States

Bites

The mouse spider Scotophaeus blackwalli does not pose any danger for humans or larger pets. Its venom is relatively weak and the spider uses its gluey silk to subdue its prey. This species of mouse spider occurs in Europe and the Western United States and should not be confused with the black mouse spiders of the genus Missulena that occur on Australia and Chile. These Australian and South American spiders are known to cause some bites of medical significance.

Distribution of the Mouse Spider in the USA

In addition to their natural range throughout Europe, the Scotophaeus mouse spider has been introduced to the Western United States and has established sizeable populations in California, Oregon and Washington. Occasionally, the spider is also seen in Nevada, Idaho, Utah, Wyoming, Colorado, Montana and Arizona.

Scientific Classification of Scotophaeus blackwalli

  • Kingdom: Animalia
  • Phylum: Arthropoda
  • Subphylum: Chelicerata
  • Class: Arachnida
  • Order: Araneae
  • Infraorder: Araneomorphae
  • Family: Gnaphosidae
  • Genus: Scotophaeus
  • Species: Scotophaeus blackwalli

Other common names:

The mouse spider Scotophaeus blackwalli is commonly also called (stealthy) ground spider.

References:

Scotophaeus Blackwalli – Mouse Spider

6 thoughts on “Scotophaeus Blackwalli – Mouse Spider

  1. I could not get a good picture because I am terrified of spiders but I feel pretty confident that this is also a mouse spider. Found on a wall in my basement in Portland Oregon.

    1. Hi Debra, thanks for getting in touch! Assuming you are somewhere in the U.S., outside temperatures should be fine for it at the moment. So it can safely be relocated outside with a piece of paper and a jar/glass.

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