Previous episodes of Bug of the Week have visited home invaders such as odorous house ants, brown marmorated stink bugs, crickets, and multicolored Asian lady beetles. About a week ago, I had the golden opportunity to witness a remarkable infestation of boxelder bugs at a vacant home. An elderly farm house had been 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 on a warm spring morning, thousands of boxelder bugs had amassed on the southern face of the house to bask in the sun. The bugs were poised to move into the landscape to search the ground for seeds. Their journey will not be far.
The farmhouse was adorned by two massive ash trees in the front yard and a large silver maple by the side door. The property was surrounded by 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. 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.
After feeding for several days, female boxelder bugs lay eggs on the bark of trees, on leaves, or on the ground. Each female can lay 200 to 300 eggs that hatch in several weeks. The tiny nymphs feed on plants during the growing season. Nymphs of boxelder bugs have black legs and short wing pads. Their exposed abdomen is red. As the nymphs mature, black wings grow longer and finally cover the abdomen as they molt to adulthood. Depending on geographic location boxelder bugs can complete one to three generations each year.
During late spring and early summer, they move to the boxelder and other seed-bearing trees. The largest populations of bugs accumulate on female trees that produce seeds consumed by the bugs. In autumn, usually in October in central Maryland, the red nymphs and the black adults collect in masses on trunks of boxelders. In the wild, adults fly and walk to rock formations, fallen leaves, or crevices in trees to gain protection from the wicked winter. In cities, suburbs, and the country, our homes provide just the right protection for winter’s respite. In autumn, swarms of bugs become a nuisance on sunny porches, siding, and around windows and doors as bugs seek overwintering locations.
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 hide, but when temperatures warm, they are active. 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. To limit the number of boxelder bugs taking up residence in your residence, eliminate hiding 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 especially kind to boxelder bugs and they flourished. Perhaps, the drought prevented a nasty bug-fungus from killing bugs as they cavorted on the ground. Maybe, trees produced exceptionally large crops of seeds. Whatever the reason, boxelder bugs are making their presence known in the Baltimore-Washington area as they prepare for another season of seed-sucking shenanigans.
We thank Ellery for finding the boxelder bungalow that served as an inspiration for this Bug of the Week. The wonderful book “Urban Insects and Arachnids: A Handbook of Urban Entomology” by William Robinson was used as a reference. To learn more about boxelder bugs, visit the following web sites.