''Marpissa muscosa'' is a species of jumping spider.
Females reach about 8–11 mm length, males only 6–8 mm. Both sexes are coloured grey to brown. The whole spider has a furry appearance and is flattened in shape.
The species builds a kind of nest under the bark of dead trees. Up to 100 of these nests can occur side by side. This spider has a hierarchy: weaker animals will show their inferiority by strutting their front legs and slowly receding from the scene.