The American Spider Beetle (Mezium americanum) is a small, odd-looking stored product pest found worldwide. It belongs to a group of beetles commonly called spider beetles due to their long legs and globular abdomen, which gives them a spider-like appearance. While primarily a nuisance in stored food facilities, this beetle can feed on a wide variety of materials, making it a persistent pest in homes, museums, and commercial storage areas.
Taxonomy and Classification
The American Spider Beetle, Mezium americanum, is classified in the family Ptinidae (spider beetles) in the order Coleoptera (beetles). The Ptinidae family is distinguished by species that resemble small spiders, often possessing long legs and antennae and a smooth, constricted thorax. These beetles are generally scavengers, thriving on dry, decaying organic material, often consuming materials of both animal and vegetable origin.
Physical Description
Adult American Spider Beetles are small, measuring approximately 1.5–3.5 millimeters in length. Their most distinct feature is their body shape: a smooth, reddish-brown, shiny, globose (spherical) abdomen and a slender thorax, contrasting with the head. This body structure, combined with their long, slender legs and antennae, makes them strongly resemble small spiders.
The larvae are small, C-shaped grubs that are whitish-yellow with dark heads. They are typically found inside the infested material where they feed and develop. Unlike the adult, the larva is less distinct and resembles many other stored product beetle larvae.
Distribution and Habitat
Despite the name, the American Spider Beetle has become cosmopolitan due to global commerce, though it is more prevalent in the Americas. As a scavenger of dried organic matter, it is found in diverse indoor habitats where food and structural materials are stored. This includes food warehouses, flour mills, museums, commercial kitchens, and residential pantries.
They thrive in dark, undisturbed areas with moderate humidity and are often found infesting food debris hidden in floor cracks, behind baseboards, under appliances, or within wall voids where other pests (like rodents) may have died or stored food.
Behavior and Life Cycle
The American Spider Beetle undergoes complete metamorphosis. Females lay eggs near food sources, which hatch into larvae that immediately begin feeding. Larvae bore into the material, often constructing a silken case or earthen cell lined with silk and excrement for pupation. The full life cycle can take several months to over a year, depending on temperature and food quality.
Adults are nocturnal and tend to remain hidden in dark crevices during the day. Their unique spider-like movement is slow and deliberate. Adults are capable of prolonged survival without food, making eradication challenging if their hidden larval breeding sites are not located.
Feeding and Damage
This beetle is an omnivorous scavenger that feeds on virtually any dry organic material. Common food sources include stored grains, cereals, spices, dried fruit, pet food, and rodent droppings. More uniquely, they are known to damage non-food materials such as wool, silk, feathers, dried leather, pharmaceuticals, and even museum specimens.
The primary damage is contamination of food products with their bodies, larval cases, and excrement. In commercial and historical settings, their wide diet range means they can cause significant, albeit often subtle, destruction of stored goods and historical artifacts.
Management and Prevention
Control for the American Spider Beetle centers on locating and eliminating the source of the infestation. This requires meticulous inspection to find hidden caches of food or dead insects within wall voids, ductwork, or under appliances. Infested materials must be disposed of or, for non-perishables, treated through freezing or heating (e.g., in a conventional oven).
Prevention relies on excellent sanitation, proper food storage in air-tight containers, and careful sealing of structural cracks and crevices where debris can accumulate. Chemical control, using residual insecticides, is typically reserved for treating structural voids after the primary source has been removed.
Conservation and Research
The American Spider Beetle is an economic pest and not a target for conservation. Research focuses on understanding its extreme dietary flexibility and survivability, as well as developing non-chemical control methods, such as pheromone traps for monitoring and identifying infestations in commercial and historical storage facilities.