In the last few days, we have been seeing a whole bunch of these strange black and orange bugs on the side of our house. They don’t seem to move much. Where did they come from? Will they leave on their own?

R. W., Deerfield, NH

Based on your description of the bug and the time of year, I would guess that your pests are boxelder bugs (Boisea trivittatus) that have left the tree where they were feeding and are now looking for a place to spend the winter.

Adult boxelder bugs are about ½ inch long and are black with striking reddish-orange lines down the middle of the back and along the margins of the wings. Small nymphs are bright red when first hatched and gradually gain the adult’s colors with each molt. Both the adults and the nymphs feed primarily on the leaves, seeds, and flowers of the female boxelder tree. They also sometimes feed on female sugar maple trees. Feeding damage is usually not noticeable and, despite their bright colors, the bugs themselves are not very noticeable either until they leave the protection of the tree and congregate together.

Why Do Boxelder Bugs Do What They Do?

Boxelder bugs plan for winter early. Normally by late summer, they are beginning to leave their host trees and are congregating in warm areas with southern or western exposures. That could be on the sides of trees, fences, or buildings such as your home. Their goal is to find a protected, warm place to spend the winter. Some will hide under siding, but many will squeeze through openings and find their way inside.

Once inside, boxelder bugs may wander until the weather gets colder, at which time they will find a place to settle in (often in wall or ceiling voids) and will become relatively inactive. They may reappear, however, on mild, sunny, winter days when they will re-enter living spaces and end up at windows or in warm corners. In spring, as boxelder trees leaf out, the bugs will all be looking for a way to get back outside. Boxelder bugs don’t feed on anything while inside but their feces may stain walls or curtains, and they can produce a disagreeable odor when crushed.

What Can You Do About Overwintering Boxelder Bugs?

Some experts say you should remove the seed-bearing female boxelder trees from your property to get rid of boxelder bugs. However, given that boxelder bugs can fly a couple of blocks, you may still get bugs from neighbors who have boxelder trees. There are measures you can take that will save the tree but kill the bugs. For large populations of boxelder bugs, trees can be sprayed early in summer when the nymphs are actively feeding. You will need a professional with a power sprayer to do that job.

Once boxelder bugs have left their trees in late summer and have grouped up on the side of your home, insecticide control may be a little less successful since some of the bugs may have already moved inside (see Boxelder Bugs Will Be Moving In!). We like to schedule our fall exterior treatment for boxelder bugs (and other fall-invading pests) in time to intercept them as they begin to make their move inside.

Utilizing pest exclusion methods can definitely help to keep boxelder bugs in their place – outside. We can caulk and seal openings on the outside of your house that the bugs use to get inside. It’s also important to tighten and repair screens and vents, add door sweeps, and remove debris around the foundation that could hide bugs. It’s not too late to discourage invading boxelder bugs. Give Colonial Pest a call today!

Photo credit: Panegyrics of Granovetter / Foter / CC BY-SA