Current Issue

Bug of the Week is written by "The Bug Guy," Michael J. Raupp, Professor of Entomology at the University of Maryland.

Boxelder bugs on the move, Boisea trivittatus


With the return of spring, boxelder bugs are out and about.


Last week we visited marvelous mason bees as they emerged from overwintering sites in logs and cardboard tubes. This week we meet another cool insect on the move with the return of warm weather. Over the past two weeks I received several inquiries concerning black and red bugs swarming on interior walls and exterior siding of homes and cavorting about in lawns. Like many home invaders, boxelder bugs are on the move seeking escape from buildings and outdoor refuges where they survived the ravages of winter. Having depleted their winter fat reserves, they seek seeds and other sources of food to fatten up in preparation for finding mates and, in the case of females, producing hundreds of eggs that will be laid on the bark of trees, on leaves, or on the ground. Later this spring eggs will hatch and tiny wingless nymphs will feed on plants during summer.

Wing buds on the sides of boxelder bug nymphs elongate with each molt.

Nymphs of boxelder bugs have black legs and short wing pads. Their exposed abdomen is red. As nymphs mature, their black wing pads grow longer and finally cover the abdomen as they molt to adulthood. Depending on geographic location, boxelder bugs complete one to three generations each year. During late spring and early summer, they move to boxelder, which is actually a member of the maple clan, and other seed-bearing trees. The largest populations of bugs accumulate on female trees that produce nutrient rich seeds, the source of food for hungry bugs.

In autumn, swarms of bugs become a nuisance on sunny porches, siding, and around windows and doors as they seek overwintering shelter. They find their way into our homes through cracks in the foundation, gaps in siding around windows and vents, and beneath doors if sweeps are in poor repair or missing. On cold winter days they are inactive, but when temperatures warm, as they have in recent weeks, restless boxelder bugs move about and make their presence known inside and out. Boxelder bugs are not harmful to humans or pets. They do not bite, sting, or reproduce indoors. However, if you squash them on your drapes or wall, they will stain. The best guidance now is to simply sweep or vacuum up these red and black rogues and dispense of them or liberate them to the outdoors.


Ever wonder what the boxelder bug’s beak looked like?

To limit the number of boxelder bugs taking up residence in your residence, eliminate overwintering places such as piles of lumber, rocks, and branches close to the house. Weatherproofing your home can also help bug-proof it. Caulk and seal vents and openings where electrical and plumbing utilities enter and exit the house. Repair or replace door sweeps and seal any openings around windows, doors, and foundation. 

For reasons known only to Mother Nature, last year was kind to boxelder bugs and they flourished. Maybe trees produced exceptionally large crops of seeds or perhaps predators were busy killing other buggy relatives such as stink bugs. Some years ago, I had the opportunity to witness a remarkable infestation of boxelder bugs at a vacant home. An elderly farm house was transformed into a boxelder bungalow through a conspiracy of construction, landscape design, and, perhaps, weather. Like many rural homes, this one was constructed of wooden frame and clapboard. Drafty windows, screens in disrepair, and a poorly chinked stone foundation provided bugs with plenty of access to the interior of the home. When I visited the property, thousands of boxelder bugs had amassed on the southern face of the house to bask in the sun. The answer to what generated this massive population of bugs was no mystery. The farmhouse was adorned by two massive ash trees in the front yard, a large silver maple by the side door, and dozens of boxelder trees in the hedgerows just a short distance away. All of these trees produce seeds used by the boxelder bugs as food.



Thousands of boxelder bugs enjoy a day in the sun at a boxelder bungalow.

In addition to silver maple, boxelder, and ash, some favorite foods of these bugs include the sap and seeds of other species of maples, plum, cherry, and many other trees, shrubs, and vines. On a recent walk near Keedysville, I was delighted to see hundreds of boxelder bugs mating and dashing about the forest floor fattening on seeds of maple and ash. Despite Mother Nature’s last whimper of winter this weekend, the bugs know spring has arrived and it is time to get busy. Beneath an ash or maple, take a moment to catch a glimpse of these curious bugs dressed in red and black.  


On the sunny forest floor, a trio of boxelder bugs sucks nutrients from a maple seed deposited last autumn.


We thank Ellery for finding the boxelder bungalow that served as an inspiration for this Bug of the Week. The wonderful reference “Urban Insects and Arachnids: A Handbook of Urban Entomology” by William Robinson was used as a reference.