The boxelder bug is a familiar fellow to many. Sadly, the first word that comes to mind about them probably has a negative connotation: something like “nuisance.” I’d like to re-set that impression of this colorful true bug by highlighting some lesser-known facts.

Boisea rubrolineata, or the western boxelder bug, lives west of the Rocky Mountains. A cousin, Boisea trivittata lives in the eastern U.S. Here’s the bad news upfront: They sometimes gather in disheartening numbers on warm walls, doors, and even inside. But they don’t hurt anything or anybody. Adults live through the winter, and they’re simply looking for a warm place to sit out the chill. 

At Mount Pisgah, I’ve found dozens of these half-inch long creatures in the crevasses of ponderosa pine bark this January. Once your eyes focus on one of them, it’s like a treasure hunt to spot more and more. Fear not: They use the deep cracks as they might use your crawl space, they don’t damage the pine. Boxelder bugs eat the leaves, flowers, and seeds of boxelder, which is a kind of maple tree. They also feed on other varieties of maple and some fruit trees. They don’t harm the trees they feed on.

Now for the interesting parts.

Boxelder bugs coordinate the timing of their life cycle to the bud and bloom cycle of their food source. Researchers think they detect when their favorite pollen is wafting through the air, then shake off the long siesta and set off looking for it. Remember, they don’t necessarily live in or even near maple trees. They’ll fly up to two miles to eat. Maybe you know someone who has this uncanny ability with pizza.

Western boxelder bugs venture out on sunny winter days. Scientists found that when they do this, the insects release chemicals called monoterpenes. These strong-smelling compounds protect the bugs from disease by killing the germs on their bodies. The bugs instinctively know the power of a sunbath will sanitize them. According to one of the papers, this behavior has never been documented in other insects. 

The insects in the sub-family Serinethinae are also known as soapberry bugs. The seed casings of their feed trees, including boxelder, when soaked in water, become soapy. Researchers are interested in the relatively fast evolutionary dance between trees and bugs. Some soapberry trees evolved seed pods or toxic chemicals to keep them safe from the bugs, and the bugs in turn developed longer proboscises and chemical adaptations. 

Here’s one last juicy fact: Boxelder bugs may not be completely vegetarian. They’ve been photographed preying on paper wasp larvae. In addition, they’ve been seen eating dead cicadas and ground beetles. So keep your eyes on the little bugs, and maybe you’ll be able to help further document and understand this behavior. 

Stay curious!

Karen Richards

Soapberry bug website: . Accessed

Research from 2012 on health benefits of boxelder bug sunbathing: . Accessed 1/20/21.