The red-headed mouse spider (Missulena occatoria) is found almost everywhere in Southern Australia, from open forests to desert shrublands. It is the largest (females up to 24 mm, males up to 12 mm) and most widely distributed Missulena species, because the spiderlings are wind-dispersed (ballooning). Normally this only occurs with araneomorph spiders, mygalomorph spiders normally disperse by walking. Mouse Spider venom may be very toxic, but few cases of serious envenomation has been recorded. Most recorded bites only caused minor effects, with funnel-web spider antivenom having proved effective as a treatment.
The spiders dig a burrow up to 55 cm deep, with two trapdoors.
While the females are black with a red tinge, the males have a bright red head and jaws, and a gunmetal blue-black abdomen.