The boxelder bug, Boisea trivittata, is a common nuisance pest in and around homes. Twice a year, in the spring and in the fall, large groups of these insects gather in warm, sunny outdoor locations. Seeing a cluster of thousands on a tree trunk or the side of a house can be quite upsetting to some people. They can also become indoor pests in the fall when they invade structures to find a place to overwinter.
Boxelder Bug Description
Adult boxelder bugs are approximately ½ inch long and mostly black in color. The abdomen of the insect, three lines on the thorax (one down the center and on each margin) and the margins of the wings are reddish orange. Immature nymphs are bright red and smaller than the adults. As nymphs approach adulthood, they begin to develop black wing pads.
Boxelder bug adults and nymphs feed on seed-bearing (female) boxelder trees and other members of the maple family. They use their piercing sucking mouthparts to extract sap from the leaves, twigs and seeds of host trees. Their feeding does little damage to the trees.
Boxelder Bug Life Cycle
Female boxelder bugs lay their eggs in the spring in the cracks and crevices of the tree’s bark. The eggs hatch when new leaves begin to appear on host trees. Boxelder bugs complete two generations per year.
Normally, boxelder bugs overwinter as adults in mulch or leaf litter around trees
or shrubs. When they emerge in the spring, they often congregate in large groups
on surfaces warmed by the sun. In the fall, second generation adults will cluster
in the same locations. As temperatures begin to cool in the fall, they begin looking
for sheltered areas in which to overwinter. Consequently, boxelder bugs that have
gathered on houses or other structures may find
their way inside.
Boxelder Bug Damage and Control
Indoors, boxelder bugs are mainly nuisance pests. They do not cause structural damage to homes or breed indoors. They do not injure people or pets, but they may spot furnishings and draperies with their excrement and omit an odor if crushed.
Boxelder bugs clustered on surfaces outdoors do not cause damage; therefore, insecticide use is rarely justified. Management should focus on keeping them out of homes. Caulking openings around windows and doors should keep the bugs from entering structures. Sanitation practices, such as vacuuming, can be used to remove any bugs that do make their way indoors.
Experts recommend removing seed-bearing boxelder trees to control boxelder bugs. Such a drastic control measure should be viewed as a last resort and may not solve the problem if there are other boxelder trees nearby.
Author: Daniel Frank, former WVU Extension Entomology Specialist
Last Reviewed: October 2018