American Spider Beetles

Facts, Identification and Control

Latin Name

Mezium americanum (Laporte)

Appearance

The American spider beetle (Mezium americanum (Laporte)), is a scavenger pest of stored food. The beetle’s name comes from the shape of the adult beetle. It has long legs and antennae. When viewed from above, it resembles a spider. It has a “humped” appearance.

The adult American spider beetle is shiny, reddish brown to almost black. Its head and thorax are covered with small hairs. The head and legs are cream colored. This beetle is often confused with the shiny spider beetle, which is completely reddish brown. There are several other species of spider beetles, including the golden, the brown, the Australian and the whitemarked.

Behavior, Diet & Habits

Since they can live by scavenging, spider beetles can survive in places like empty warehouses. In these situations, they feed on old rodent droppings and other debris. They are pests in mills, food processing facilities and museums. They can infest bird and rodent nests. If the nest happens to be in the attic or crawl space of a home, the beetles can easily move into the living space.

Reproduction

Adult spider beetles deposit their eggs in the material that the larvae will eat after they hatch. This may be broken grain or flour and grain products. They also feed on hairs, feathers and even droppings from birds or mammals. Spider beetles seem to be attracted to moist, damp areas. They eat products that are moldy or products that have been stored too long to be usable.

The larvae are curved and whitish in color. They spin silken webbing on the surface of the food as they eat. They also spin silken cocoons where they change to adult beetles.  The adult beetles are usually active at night or in dark places, so they are difficult to see. Holes in packages, webbing in food, and silken cocoons are all signs of an American spider beetle infestation.

Signs of an American Spider Beetle Infestation

Boxes or packages with small 1 to 2 mm size holes, as well as round silk cocoons that are about 4 mm in size. Another sign would be the small adults.

More Information

Controlling spider beetles in homes starts with a thorough inspection. Throw away all infested food. Vacuum pantry and cabinet shelves thoroughly. This will remove any food residue that larvae might eat.  Vacuuming will also remove any beetles that are still in their cocoons. Store new food products in sealed containers.

Insecticide will be most effective if it is applied into cracks and crevices or voids. For product selection and application, it is usually best to contact a pest control professional.