Adult Carpet Beetles Seen Indoors Mainly in Spring

It's spring and time for the calls about tiny, dark, round bugs crawling up walls. Although these “bugs” are only about the size of the head of a pin, closer inspection reveals that they are beetles.

The small dermestid carpet beetles (varied carpet beetle, common carpet beetle, furniture carpet beetle, black carpet beetle) have life cycles closely tied to the season. They also have a life cycle that often requires both an indoor and outdoor stage.

The larval stage is the damaging stage that feeds on wool, hides, hair, dead insects, food crumbs, household lint, and general detritus. The adults, however, feed on the nectar and pollen of flowering plants. That's why they are climbing walls toward light, looking for a way to get outside. That's also why we don't see them until spring when plants are starting to flower.

When the adult beetles emerge from their pupal stage in early spring, they are attracted to light at first (and they can fly). After the female beetle gets outside, feeds on pollen, and mates, she then avoids light.

At this time, she is looking for a suitable place to lay eggs and is often drawn to the darker spaces indoors. Apparently not all carpet beetle females require pollen or nectar in order to lay eggs. Researchers have found evidence of some indoor strains that seem to breed year round without access to pollen.

If you look at the adult carpet beetles under magnification, you will see that they are actually quite colorful, with the exception of the black carpet beetle. The other three are various calico combinations of brown, white, orange, and black, depending on the species.

They are 1/16 to 1/8 inch (1.6 to 3.2 mm) long, and rounded in shape. Carpet beetle larvae are yellow-brown, about 1/4 inch (6.4 mm) long, and covered with bristly hairs. They avoid light and remain hidden, although you may find their shed skins.

If you have a customer with a recurring carpet beetle problem, it may not be that you've missed something inside. Part of the problem may be that the beetles are reinfesting from flowering plants outside. In some cases, the unsuspecting homeowner may even carry the beetles inside on cut flowers from the garden.

Some of the favorite flowers of carpet beetles are dogwood, spirea, crape myrtle, pyracantha, buckwheat daisy, wild aster, and ceanothus. Animal nests, including wasp and bee nests, are another outside (or inside) source of carpet beetles.