Boxelder Bug

Boisea trivittatus
Family

Rhopalidae (scentless plant bugs) in the order Hemiptera (true bugs)

Description

A blackish bug with a flattened back with red markings, sometimes in the form of an X on the back, plus a red line along the outer edge of the closed wings. There are noticeable veins on the membranous portion of the forewings. The immature stages are bright red with black legs and slate-gray or blackish wing buds (the tiny, immature wings).

Size

Length: to ½ inch.

Habitat and conservation

Boxelder bugs are found in proximity to their food plant, the box elder tree, and occur wherever those trees are found—forests, bottomlands, yards, parks and more. In autumn you may see hundreds of these bugs crawling on the outside (usually the south-facing side) of your house, seeking winter shelter. They go dormant as the weather gets colder, but if they are warmed by your home’s heating, they may revive and enter your house, mistaking its warmth for springtime.

Foods

Like many other true bugs (such as cicadas, aphids, stinkbugs and leafhoppers), boxelder bugs have strawlike mouthparts adapted for sucking plant juices. The preferred food plant is box elder (Acer negundo), though they are sometimes also found on other maples, especially silver maples, and ash trees. Generally, they feed on the soft, leafy parts of the trees. Oddly enough, boxelder bugs rarely hurt their host trees.

image of Boxelder Bug Distribution Map
Distribution in Missouri

Statewide.

Status

Common. Their occurrence is linked to proximity of food plants, so an area with many box elder trees will have more boxelder bugs than an area with none or very few.

Life cycle

Like many insects, this species molts through a number of immature stages before a final molt in which they emerge as a winged, sexually mature adult. In autumn, large nymphs and adults congregate at protected overwintering sites, such as box elder bark, or the siding of a house. At the end of March they emerge from their dormancy, and near the end of April they begin laying eggs, again in crevices of box elder tree bark.

Human connections

If boxelder bugs “bug” you, consider removing nearby box elders and silver maples. Vacuuming, swatting and using sticky traps can help. Insect-proof the house (screen the vents, caulk cracks, etc.). If you use an insecticide, make sure it works on this species and follow the directions carefully.

Ecosystem connections

It is believed that the red markings on the boxelder bug warn predators that it is distasteful, but there are many predators, such as praying mantises and some spiders, that readily eat them.