ARTHROPOD MUSEUM NOTES
Number 105 • March 26, 2014 • Jeffrey K. Barnes
Variable carpet beetle
Genus and species: Anthrenus verbasci (Linnaeus)
The varied carpet beetle is a serious pest of stored organic products in homes, warehouses, and museums, and it has a virtually worldwide distribution. The larvae feed on a variety of dry protein of both animal and plant origin, including woolen goods, furs, leather, stuffed animals, mounted insect specimens, feathers, horn, silk, grains, and spices. Dead insects and spiders are favored larval food sources. Wasp nests provisioned with spiders and insects, spider webs, and museum insect collections are often targets of carpet beetle larvae. Larvae also scavenge in nests of birds and bees, where they feed on feathers and stored pollen.
Adult varied carpet beetles are two to three millimeters long. They are black with a zigzag pattern of white, brown, and dark yellow scales on the wing covers. They emerge in late May and early August. They visit many kinds of flowers, but they are especially associated wit hthe umbellate flowers of the family Apiaceae, where they feed on pollen and nectar. Outdoors, females search for spider webs with ensnared insects; bee, wasp, and bird nests; and other food sources that can sustain the larvae. There, they lay eggs. Indoors, females place eggs on or near dried organic goods. As temperatures turn cold, adults seek shelter, often entering structures. Adults live only two to four weeks.
Eggs hatch in spring or early summer after a two to three week incubation period. The number of larval molts is highly variable, but it averages around seven or eight. The total larval period varies from less than a year to nearly two years, depending on temperature and food quality. Mature larvae are four to five millimeters long. They are covered with dense tufts of bristles which they extend upright to form a round plume when disturbed. Shed bristles can cause itchy welts in susceptible people, and these are sometimes confused with bedbug bites.
There is usually one generation per year, both outdoors and indoors, but if conditions are not optimal, the life cycle might last for two or three years.
Varied carpet beetles are most harmful during the hottest months. Indoor populations can be limited by inspecting susceptible materials and vacuuming up the pests or trapping them using ultraviolet light. Infested products can be treated with low or high temperature regimes. Experimental evidence has shown that exposure to a temperature regime of -20°C for six hours is sufficient to achieve 100% mortality of eggs, larvae, pupae and adults.