Meet the Boxelder Bug

Features - Pest Profile

These fall-invading pests enter structures looking for protective overwintering sites.

September 5, 2019

©Kevin Wells | AdobeStock

By Sandra Kraft and Larry Pinto

Editor’s Note: This article was reprinted with permission from Techletter, a biweekly training letter for professional pest control technicians from Pinto & Associates. To subscribe, visit

The boxelder bug, Boisea trivittata, and the western boxelder bug, Boisea rubrolineata, are found across the U.S. and Canada and wherever boxelder trees are found. Structures that are near a female boxelder tree can be inundated with these bugs in the fall.

Adult boxelder bugs are about ½-inch (11-14 mm) long; the western species is slightly smaller. Adult bugs are black with red-orange wing edges, red lines on the back and red eyes. Newly hatched, wingless nymphs are mostly reddish and add more black coloration with each molt. Both the adult bugs and the nymphs feed on seed pods, leaves and flowers of the female boxelder tree or sometimes female silver maple trees. Feeding damage is not usually very noticeable.

PEST STATUS. Boxelder bugs are another of the fall-invading pests that enter structures looking for protective overwintering sites. They can fly a couple of blocks from their host tree to enter homes through gaps around windows, vents, rooflines, etc. Once inside, boxelder bugs may wander until the weather gets colder, at which time they will find a place to settle in (often in attics, wall voids or ceiling voids) and will become inactive. They will make a reappearance indoors in early spring (or sometimes on warm, winter days) as they look for a way to get back outside.

©Melinda Fawver | AdobeStock

The best control is to remove female (pod-bearing) boxelder trees, when possible. Male boxelder trees are not affected. Boxelder trees are not normally considered to be very attractive or desirable trees and probably won’t be missed.

Boxelder bugs sometimes can be controlled by power-spraying the trees in early summer when nymphs are feeding. Another control opportunity occurs in early fall when adult bugs cluster on lower tree trunks or on sunny foundation walls before moving into overwintering sites. As with other fall-invading insects, cleaning up foundation debris (and in this case, boxelder seed pods) and sealing entry points on the structure is important. Once the bugs are inside and in hiding, control is difficult. Boxelder bugs can be removed with a vacuum cleaner but can give off a foul defensive odor if crushed. Their reddish feces may stain fabrics.

Key Points to Remember: Boxelder bugs are seasonal overwintering pests that can become active on warm winter days. They do not reproduce indoors. The best controls are removal of female boxelder trees or utilizing other outdoor measures, including pest-proofing, before the bugs move inside.

The authors are well-known industry consultants and co-owners of Pinto & Associates.