Adults are about 1/32 to 3/16 inch long depending on species. They have a spiderlike look with long, thin legs and threadlike antennae. The wing covers (elytra) can be hairy, scaly, pitted, or shiny smooth and are wider than the prothorax. Mature larvae are 1/8 to 3/16 inch long, white, C-shaped grubs with 3 pairs of thoracic legs visible.

Eggs are laid in and around the larval food source, where larvae develop. They spin a silken cocoon some- what away from the food source for pupation. The life cycle length varies greatly among species.

Spider beetles are scavengers that tend to appear in places where foods have been left behind, including broken grains, grain dust, seeds, rodent droppings, dried carcasses, museum species, bat guano, hair and lint in cracks and heat ducts, and dried plant materials. They also thrive in wasp and bee nests and are associated with some bat species. In the author's experience, American spider beetles are frequently found in buildings that have been heavily baited for rodents.