any member of about 500 species of insects sometimes considered a part of the family Anobiidae (order Coleoptera) and sometimes placed in their own family, Ptinidae. These spider-shaped beetles have a globular body, long thin legs, and no wings. They range in colour from reddish brown to black and in size from 1 to 5 mm (0.04 to 0.2 inch).

Spider beetles, which occur throughout the world, live in plant or animal remains, stored food products, dry wood, and museum specimens. The white-marked spider beetle (Ptinus fur) and the shiny American spider beetle (Mezium americanum) are household pests in North America.