Scotophaeus blackwalli is a ground spider of the Gnaposidae family. They are somewhat common in the Western United States. It is not venomous like other mouse spiders found in Australia of the genus Missulena. Its abdomen is mostly gray and covered in a velvety coat, like the fur of a mouse. The cephalothorax and legs of this spider are usually in a lighter colour, either brown or gray. The body of the spider can sometimes appear shiny even though it is covered with fine hair. Being a ground spider, its body almost appears to be lower than its legs as it moves, its underside is right at ground level. Scotophaeus blackwalli is a medium-sized spider. Females reach a body size of up to 12 mm, and the males are a bit smaller.
These spiders do not build webs but are hunters that stalk and attack their prey. They hunt at night looking for small insects they can catch. Mouse spiders will also feed on other spiders. They produce sticky silk with their oversized spinnerets which they quickly entangle their prey with. This allows them to capture prey that is much larger than them like other spiders, they build silk cocoons for their eggs.
The Scotophaeus blackwalli spider does not pose any danger to humans or larger pets. Its venom is relatively harmless unless you are quite small. This mouse spider has been introduced to the Pacific Northwest including southern Vancouver Island. They have developed sizable populations on the coast of southern BC. They are appearing more often in our homes.
Although we call them mouse spiders, The use of this common name is not ‘accepted’ by arachnologists because there is a genus of spiders (Missulena) that are called mouse spiders. They are not only in a different family but in a separate infra-order, (Mygalomorphae), which also includes tarantulas and trapdoor spiders.