Boxelder bugs

Boxelder bugs can sometimes occur in large numbers both inside and outside the home. While attractive to look at, they can be annoying especially when they leave marks from their excrement on curtains, furnishings or clothing. In addition, when crushed, they give off a very unpleasant odor.

Common types

Boxelder bugs are found in most parts of the United States. Although there are other closely related insects that look like them, including the milkweed bug, none are likely to congregate in huge numbers like boxelder bugs. These insects belong to the order Hemiptera or true bugs, which are characterized by the possession of piercing mouthparts specially adapted for sucking the juices of plants or animals.

The boxelder bug feeds on woody plants and herbs and originally earned it’s name because it was found to infest boxelder trees although this insect now also infests many other species of trees including maple, apple and almond. In the US two species predominate, the Eastern Oxelder bug (Boisea trivittatus), which is found east of the Rocky Mountains, and the Western Boxelder bug (Boisea rubrolineatus), which is found west of the Rockies.


The adult Boxelder bug is about ½ inch in length and brownish-black in color with three red stripes on the thorax and several fine red lines on the wing margins. The abdomen is also bright red. The wings lie flat on the back when at rest.

Boxelder bugs usually feed on the leaves, flowers, and seedpods of the female or seedbearing boxelder tree (Acer negundo). They may also occur on male boxelder trees and occasionally occur on maple and ash trees. Boxelder bugs can feed on the fruits of almond, apple, cherry, peach, pear, and plum trees, and on grapes, where their feeding punctures can cause the fruit to become deformed. Large numbers usually occur only on seed-bearing female boxelder trees.

Boxelder bugs pass the winter in the adult stage in dry, sheltered places where they accumulate in large numbers. They often choose buildings or houses as a protected place to over winter. When the weather warms up in the spring, these insects leave their places of hibernation to fly to boxelder trees where they lay their eggs (which typically hatch in 10-14 days) in crevices of tree bark or on leaves, grasses and on other objects near host plants. Eggs are yellow when first laid and become a rusty red color as the nymphs develop inside. The young nymphs are bright red with the head end tending to be darker. When the nymphs are about half-grown they become marked with black and begin to develop black wing pads. Nymphs feed in the same way as adults by inserting their proboscis (mouthparts) into leaves, fruits or soft seeds and sucking out the plant juices. Feeding continues throughout the summer and the nymphs gradually mature becoming adults as cold weather approaches in the fall. There are 5 nymphal instars or stages before the adult appears. In some areas there may be two generations per year, one reaching maturity in mid-summer and the second one in early fall. Most of the nymphs of the second generation mature to adults by fall where they look for dry sheltered places to over winter such as hollow tree trunks or in cracks and crevices in walls.

Health issues

Boxelder bugs are attracted to lights and will readily fly in through open doors and windows. While they do not cause direct injury to people, pets or buildings, periodically populations can soar. Large populations of boxelder bugs can be annoying and insects can spot curtains, furnishings, and clothing with their excrement. When crushed, they give off a foul odor. They do not breed indoors and if trapped in basements or houses, they will eventually die. Boxelder bugs do little damage to ornamental trees although they may occasionally cause puckering or distortion of fruit in commercial orchards, but this is rare and not a significant problem.

Boxelder control

Elimination of Host Trees

Since the presence of these boxelder bugs is primarily associated with boxelder trees, replacement with other tree species is one method of eliminating this insect. If boxelder trees are present, it may be best to keep only the male or staminate trees and remove the female, pistillate or pod-bearing trees to help reduce insect numbers. However, elimination of trees on a property won’t always completely resolve the problem. Full-grown, winged adults can fly some distance, so boxelder bugs may also migrate in from neighboring trees. If removal of trees is not an option, fallen seeds can be removed from beneath and near trees.

Exclusion and Sanitation

Repairing torn screens and filling places where insects can enter the house, such as cracks around doors and utility pipes can help prevent insects entering the home. Any boxelder bugs that enter the home may be controlled by hand-collecting or vacuuming. Hiding places such as piles of rocks, boards, leaves, and general debris close to home should also be removed since boxelder bugs hide during the day or can over winter in these sites.

If large numbers of insects are found on walls or tree trunks these can be washed off with a forceful stream of water, and since boxelder bugs are susceptible to drowning large numbers will be controlled in this way. Smaller clusters of bugs may be killed by pouring boiling water on them, but be careful to avoid killing grass and other desirable plants

Chemical Control

Insecticide sprays are generally not required for the outdoor control of boxelder bugs, and are often no more effective than vacuuming and hosing. Insecticidal soap applied in a forceful spray of water may reduce populations on tree trunks. Suitably labeled pyrethroid insecticides may be used to treat foundation walls around the perimeter of buildings or for application to tree trunks and branches. Indoor control of boxelder bugs is often difficult since insects tend to be scattered throughout the house. Crawling insect killer aerosol sprays labeled for boxelder bugs may provide temporary control of indoor infestations. Cracks and crevices, wall voids and similar areas may also be treated with dusts and/or aerosols.

Before using any insecticide, always read the label, follow directions and safety precautions.

When applications are needed on tall trees or to large areas requiring specialized equipment, it is best to employ a reputable pest control firm.