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