Scotophaeus blackwalli, also known as the mouse spider, is a species of spider belonging to the family Gnaphosidae.

The adult males of these spiders reach 9mm in length, maturing in the early summer, while females reach 12mm, and can be found until autumn. The carapace is dark brown while the abdomen is brown/grey with hairs resembling the body of a mouse, hence the common name of 'mouse spider'. The legs are brown with thick pubescence. The male has a small scutum on the dorsum of the abdomen.

This species is widespread in Britain and northern Europe. They are commonly found in Britain around and inside houses, usually in the Autumn, and also under bark and in holes in walls in warmer parts of Europe. It hunts nocturnally.