Boxelder Bug Facts, Identification and Control
Family: Rhopalidae (scentless true bugs)
Species: Boisea trivittata
Size: ½ inch (around 12mm) long fully grown; nymphs are around 1.3 mm long
Color: Black or dark grey 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.
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.
Adult boxelder bugs overwinter in sheltered places where they can keep warm. They remain mostly inactive until boxelder trees start filling in and/or the air temperature consistently reaches 70 degrees. When these conditions are met, boxelders fly to nearby host trees, mate, and lay hundreds of tiny eggs on the tree or on fallen seeds near it.
Boxelder eggs typically hatch in 10 to 14 days. Boxelder nymphs resemble fully-grown boxelder bugs, but they’re smaller and haven’t developed wings. The nymphs remain close to their host trees and feed on its foliage and seeds by inserting their sucking mouthparts directly into the tissue of the plants.
Nymphs continue to feed throughout the summer, until they gradually mature into adults. Boxelder maturation rate depends on outdoor temperature; the warmer it is, the faster nymphs will grow up.
Boxelder adults begin to seek out warm, sunny places starting in early fall. This is when most homeowners notice the bugs as nuisance pests, because as winter approaches, boxelders seek out sheltered, warm places where they can survive the cold.
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.
Boxelders are attracted to structures with large western or southern exposure, because those structures will be in sunlight longer.
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.
Signs of Infestation
Boxelders bugs infest most buildings in the fall, when they’re looking for a place to survive the winter. Depending on ease of access and the size of nearby boxelder populations, you may notice up to hundreds of boxelders infesting your building.
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.
Look for boxelder swarms around windows, especially on parts of the building with western or southern exposure, or in any other outdoor area that’s in the sun for most of the day.
Boxelders seek out hiding places in warm, humid, and out-of-the-way parts of buildings. They’re common in garages, basements, attics, crawlspaces, boiler rooms, rooms with detached heating, garbage rooms, or other storage areas.
Treatment and Prevention
Vacuum up swarms as you find them, and discard the vacuum bag when you’re finished. During very active periods you may have to do this every day, but it will be effective.
Spraying the surfaces boxelders congregate on with bleach and water may deter swarming. Spray outdoor swarms away from your building using a hose.
Boxelders enter structures through cracks and crevices, usually in door and window frames or around utility lines. Sealing these gaps with caulk or steel wool is the best way to prevent boxelders from getting in.
Cover and elevate firewood, clear outdoor clutter (especially boxelder seeds), and trim nearby plants to deprive boxelders of hiding spots and make your building less appealing.
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
University of Idaho Extension “Boxelder Bug Nuisance Management for Homeowners,” by Danielle Gunn and Edward John Bechinski
University of Minnesota Extension “Boxelder Bugs,” by Jeff Hahn and Mark Ascerno
The National Pesticide Information Center’s Pest Control Information Database Entry on Boxelder Bugs
Iowa State University Extension and Outreach Bed Bugs Encyclopedia article