Spider beetle are so named because some species actually resemble small spiders in appearance with their small head and prothorax and larger abdomen. The shiny spider beetle, Gibbium psylloides and the American spider beelte, Mezium americanum, in particular, resemble spiders due to their globular-shaped abdomens. Other spider beetle species found in the Ptinus have abdomens that are more elongate. The head of all spider beetles is generally concealed under the prothorax when viewed from above.

Biology and life cycle

Worldwide, about 30 species of spider beetles in the family Ptinidae are pests of food products. Spider beetles are typically found in cooler, northern regions of this continent preferring temperature of 25°C or below. The highest temperatures at which these beetles survive is 30°C and adults quickly die at temperatures above 38°C.

Spider beetles are more commonly in warehouses and homes, although occasional infestation may be found in a floor mills, food processing facilities or museums. Infestations are often prominent in older, wooden buildings, especially those with damp basements. Only the spider beetles in the genus Ptinus have functional wings, but only a few species of this group will actually fly. Spider beetles most often move about by crawling and will commonly feign death when disturbed by drawing their legs up to their bodies.

Spider beetles prefer the dark and are most actives at night. If the room stays dark most of the time, however, spiders will remain active around the clock. During daylight hours, the beetles will harbor inside crevices, in between food packaging, and other darkened areas. Activity is greatest at cooler temperatures. When stacks of food items are infested, the activity will be toward the outside of the stack rather than the interior. Heavily infested bags of food items may become covered by the silken pupal cocoons spun by the larvae.