Spider beetles belong to the beetle family Ptinidae. They got the name “spider” because of their appearance. They resemble mites or small spiders because they have long legs and round bodies. The head is usually hidden when the beetle is viewed from above.
The American spider beetle, Mezium americanum (Laporte), is dark-colored –reddish-brown to black. The head, legs, and antennae are cream or golden colored and covered with hairs. Many people confuse this beetle with the shiny spider beetle, which is completely reddish brown. The adult beetle is usually less than 1/8″ long.
Spider beetles are attracted to moisture. They are scavengers and often feed on animal manure. They seem to be able to thrive in cool environments and they are often found in warehouses and old buildings.
Many infestations of American spider beetle begin near the nests of birds or rodents. These can be in attics, crawl spaces, basements, or even outside on the eaves. The larvae feed on hair, feathers, and droppings. The larvae have even been found feeding on old rodent bait. As the beetle population grows, the beetles migrate into other parts of the home or building.
In food processing facilities, the larvae feed on seeds, broken grains, grain products, and dried fruits. In homes they can feed on grain products, wool, hair, furs, feathers, dried flowers, and dead insects.
The larvae often make silken webbing where they are feeding. The larvae burrow into boxes or items made of wood to make a chamber where they will change into adults. They spin cocoons inside these chambers. The adults often hide in dark places and move about at night. The silken webbing of the larvae is often the first clue that there has been insect activity.
Control of American spider beetles begins with a thorough inspection. It is important to find everything that the larvae are eating. The beetle populations are often small, so removing the infested material may solve the immediate problem.
If the insect population is large, insecticide applications may be necessary. Aerosol or liquid insecticide can be applied into cracks and crevices. Dust insecticide can be effective in voids, like inside of walls. These applications may require specialized equipment to avoid spills and misapplication.
Because the source of the infestation is often in an inaccessible area, many people prefer to have a pest control professional help with the inspection. The pest control professional will have the products and equipment to make the insecticide applications.