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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.

There’s no place like home for the holidays - Boxelder bugs, Boisea trivittatus

A pair of boxelder bugs will soon leave this tree to find a sheltered spot to spend the winter

Last week while addressing a garden club, one somewhat distraught gardener asked about a horde of black and red insects amassing on the southern side of her home. Each day a small but steady stream of these nosey bugs appeared indoors on the walls and windows. What were those bugs and why were they invading her home? Thanksgiving marks the beginning of the Holiday season, a time of homecoming for family and friends. This season is also a time of homecoming for many six-legged guests like the red and black boxelder bugs visiting my troubled gardener. Boxelder, also known as ash-leaved maple, is a rather common native tree and one of the favorite foods of boxelder bugs. Like the golden rain tree bug we met a few weeks ago and 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 in a protected spot like someone’s home. During the growing season, tiny boxelder bugs ate 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 the boxelder trees, especially to female trees. Female boxelders bear winged seeds and male trees do not. The largest bug populations tend to build up on female trees where they feed on seeds.


On a warm November day, boxelder bugs plot the best route to enter my home.

In autumn, usually October or November in central Maryland, nymphs and adults collect in masses on trunks of boxelders. 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, 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 homes through cracks in the foundation, gaps in siding around windows and vents, and beneath doors if sweeps are in poor repair or missing.

A boxelder bug on wall or window heralds the approaching Holiday season.

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, a rather unpleasant stain will result. To limit the number of boxelder bugs coming to your home for the holidays eliminate hiding places such as piles of lumber, rocks, and branches close to the house. As with other home invaders like multicolored Asian lady beetles, brown marmorated stinkbugs, and crickets, 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 foundation. Despite my best efforts to exclude boxelder bugs from my home, one or two always appear indoors my wall or window about this time of year. An annual visit by this small harbinger is a pleasant reminder of homecomings, fun, and festivities of a Holiday season just around the corner. Have a wonderful Thanksgiving!



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