Drugstore Beetles

When I first read the name drugstore beetle, I conjured up images of an 1800s mercantile being harassed by a gunslinging beetle wearing spurs. I have no idea why. ​

Adult drugstore beetle (Siga) CC BY-SA 3.0

The truth is, drugstore beetles (Stegobium paniceum), also known as biscuit beetles or bread beetles, are very tiny and don’t look like much of a threat to anyone. Looks can be deceiving.

Drugstore beetles got their name because, until relatively recently, most drugstore pharmaceuticals were made out of dried plants. Drugstore beetles have also been known to feed on chemicals, such as strychnine, once commonly found in drugstores.

Drugstore beetle description

Being brown and covered with microscopic hairs, drugstore beetles look similar to cigarette beetles, but are somewhat larger at 1/8” (3.5mm) in length. Also, where cigarette beetles have smooth bodies and serrated antennae, drugstore beetles have longitudinal grooves along the elytra (wing cases) and antennae that end with three tiny segmented clubs. Drugstore beetle larvae are white grubs with very fine hairs.

Drugstore beetle. Note the size of the beetle as compared to fingernail. (Kamran Iftikhar) CC BY-SA 3.0

Drugstore beetle lifecycle

Female drugstore beetles can lay up to 75 eggs at a time, and the egg-laying season can last for months. That works out to a tremendous number of offspring. Those eggs are usually laid in dried foods, such as cereals, dried fruit, grains, herbs, and nuts. Eggs may also be found in dried meat, hair, wool, and candy.

As those eggs are laid, they are covered with a yeast fungus. This fungi and the beetles cannot live without each other. This is an example of obligatory symbiosis. In less than two months, larvae pupate into adulthood, protected by tiny cocoons, and the cycle begins again.

Damage caused by drugstore beetles

After the eggs hatch, it is the larvae that cause damage by burrowing through and feeding on a wide variety of materials. They also leave frass (big poop) and webbing behind, as well as stray hairs and secretions.

Drugstore beetle larvae love dried plant products, such as cereals, beans, pasta, rice, bread, flour, and spices. Apparently, paprika and chili powder are drugstore beetle favorites, though they will eat practically anything. Larvae are also commonly found in tea, potpourri, tobacco, wreaths, and birds’ nests and they have been known to damage books, leather, hair, and museum specimens.

In the garden, drugstore beetles are a major pest of cumin.

Drugstore beetle control

Drugstore beetles are often carried into the home, garden, or landscape in bulk items, such as grass seed, bird seed, or dry pet food. They may also hitch a ride on packaged food. This is why it is important to look for holes in food packaging and avoid those products. While adult drugstore beetles do not eat, they often chew holes in plastic, foil, and paperboard food packaging. You may also see pockmarks in crackers and pasta. Inspecting foodstuffs and bulk items before you bring them home can prevent infestation.

When bringing crops, such as beans and other seeds, into the home., it is a good idea to freeze them overnight to kill any larvae that may be lurking. This is an easy way to keep your home from becoming infested. Diatomaceous earth (DE) can also be used lightly in areas where drugstore beetles may be lurking.

Pheromone traps and insecticides are not effective against drugstore beetles.