- The boxelder bug is a common pest of box elder trees (Maryland Biodiversity Project), also known as ash-leaved maple.
- Adult bugs are oval in shape and about ½ inch long when fully grown. They are dull black and marked with red along the edges of the front wings.
- The immature bugs, called nymphs, are also red and black. The legs and short wing pads of the nymphs are black. The exposed abdomen is red. As the nymphs mature, the black wings grow longer and finally cover the red abdomen in the adult stage.
- Eggs hatch into nymphs in late spring and early summer.
- They primarily feed during the summer on leaves, twigs, and seeds of boxelder trees and sometimes other types of maples. Boxelder trees have separate male and female trees. Female trees bear winged seeds (samaras) and male trees do not. The largest bug populations tend to build up on female trees. These trees are not damaged by the feeding activity of the bugs.
- In the fall (usually October in central Maryland), the red nymphs and the black adults collect in masses on the trunks of boxelder trees near the ground. They will sometimes congregate on landscape mulch but are not causing damage to plants.
- Adults later fly away to hibernate in buildings, rock piles, fallen leaves, or other sheltered places. At this time the bugs become a nuisance to residents.
- Swarms of bugs can be found on sunny exposures on porches, windows, door frames, and on the siding. They prefer white surfaces on the south side of buildings. They hide in cracks during cold weather but can become active on warm days during the winter.
- Bugs can find their way through cracks where they become a nuisance indoors. The boxelder bug is not harmful to humans or pets. It will not bite or reproduce indoors. However, there are reports that squashed bugs will stain fabrics.
Boxelder bug adult and nymphs. Photo: William M. Ciesla, Forest Health Management International, Bugwood.org
- Eliminate hiding places such as piles of lumber, rocks, and trash close to the house to help reduce an infestation.
- Weatherproofing, tightening up windows, doors, and caulking entry points will help to prevent entry.
- Vacuum or sweep up any bugs that enter the house. Discard them or release them back outdoors.
- Spraying them in the landscape is not necessary or recommended.