Boxelder Bug Facts, Identification and Control
Family: Rhopalidae (scentless true bugs)
Species: Boisea trivittata
Size: ½ inch long fully grown; nymphs are around 1.3 mm long
Color: Black wing covers, upper body, legs, and antennae, with three bright red or orange striped markings running along the head, body, and wing tips in a vaguely ‘X’-shaped pattern. Red or orange lower body beneath wing covers.
Signs of Infestation
Boxelders bugs infest most buildings in the fall, when they’re looking for a place to survive the winter. Depending on the ease of access, you may notice up to hundreds of boxelders near your building. Look for swarms of boxelders around windows, particularly windows with western or southern exposure.
Boxelders’ produce a liquid feces, which may stain carpet, rugs, or other fabrics. These stains will be small and faded yellow, brown, or grey in color. Boxelders may also stain nearby surfaces when crushed. Stains are most noticeable near areas congregation like window sills and door frames.
Treatment and Prevention
Boxelders enter structures through cracks and crevices, usually around door and window frames or utility lines. Sealing these gaps with caulk or steel wool is the best way to prevent boxelders from getting in. Start looking for gaps around areas outside the building where boxelders congregate, such as windows.
Vacuum up swarms of boxelder bugs as you see them. Discard the vacuum bag when you're finished. Wash off the areas where boxelders congregated with soap or bleach and water. Clear away as much outdoor clutter as you can, and trim nearby plants to deprive boxelders of attractive hiding places.
Behavior and Diet
Boxelders primarily feed on the seeds of boxelder trees, though they can also suck the sap out of the trees’ leaves and twigs. Only female boxelder trees produce the winged seed pods commonly associated with boxelder trees, so most large boxelder populations gather around them during feeding season.
Though they prefer boxelder trees, boxelder bugs can also feed on the seeds of other trees in the acer family, including maple and ash trees. Because they primarily eat seeds, boxelder bugs don’t inflict significant damage on the trees they infest.
Reproduction and Life Cycle
Boxelders mate in early summer and lay eggs on seed-bearing boxelder trees in July. Eggs typically hatch within 10 to 14 days. Boxelder nymphs remain close to host trees and feed continuously through summer, gradually maturing into adults by fall. The warmer it is outside, the faster boxelder nymphs grow.
When fully grown, boxelders seek out warm, sunny places to congregate. Boxelder adults spend to spend winters dormant inside warm, sheltered areas. Around April or May the following year, boxelders will come out of dormancy, leave their shelters, and seek out mates.
Though fully-grown boxelder bugs can fly, they usually crawl from place to place.
In the fall, it’s common to find large ‘swarms’ of boxelder bugs bunched up on a window or sunny surface. These swarms group together to keep warm and cover the surface area of a desirable, warm surface.
Although boxelder feeding doesn’t permanently damage trees, if enough boxelders feed on a host tree, they may distort its foliage by depriving it of essential plant fluids. Severely infested foliage may take on a yellow hew or shriveled appearance.
Cornell University Department of Entomology’s Insect Diagnostic Laboratory Boxelder Bug Fact Sheet
Penn State College of Agricultural Sciences Department of Entomology’s Insect Advice on Boxelder Bugs
University of Maryland Extension Home and Garden Information Center “The Boxelder Bug,” by Michael J. Raupp, UM Extension Entomologist