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

Red and black, Boxelder bugs: Boisea trivittatus


Boxelder bugs bask on bricks before entering the home.


With all of the flap about brown marmorated stink bugs, it’s time to visit another home invader. This one, dressed in red and black, is a native insect called boxelder bugs. Boxelder, also known as ash-leaf maple, is a rather homely native tree and one of the favorite foods of boxelder bugs. Like their other “true bug” relatives, boxelder bugs have a beak with sucking mouthparts used to remove plant sap and the contents of seeds. In early spring, nymphs of boxelder bugs hatched from eggs laid by mothers that survived the winter. 

The seeds of boxelder are one of the favorite foods of boxelder bugs.

During the growing season, boxelder bugs eat the sap and seeds of boxelder and other species of maples as well as ash, plum, cherry, and many other trees, shrubs, and vines. Boxelder bug nymphs have black legs and short wing pads. Their exposed abdomen is red. As the nymphs mature, the black wings grow longer and finally cover the abdomen as they molt to adulthood. During late spring and early summer, they move to boxelder trees, especially to female trees. I’ll bet you didn’t know that in some species, trees are male or female, and in other species, trees are both male and female. How strange is that? Female trees bear winged seeds and male trees do not. The largest boxelder bug populations tend to build up on female trees, where they feed on seeds.

Two boxelder bugs prepare to leave a boxelder tree to find an overwintering spot.


In autumn, usually October in central Maryland, the red nymphs and the black adults collect in masses on trunks of boxelder trees. In the wild, adults fly 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 from the cold. Swarms of bugs become a nuisance on sunny porches and siding and around windows and doors. 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 become 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, then they will stain.

To limit the number of boxelder bugs taking up residence in your home, eliminate hiding places outdoors such as piles of lumber, rocks, and branches close to the house. As with other home invaders like brown marmorated stink bugs and crickets, you should weatherproof your home to help solve the problem. Caulk and seal vents and openings where electrical and plumbing utilities enter and exit the house. Repair or replace doorsweeps and seal any openings around windows, doors, and foundations. This will help save energy and help reduce headaches when this diminutive army of red and black storms your barricades.


To learn more about boxelder bugs, visit the following web sites: