What are these strange bugs that suddenly showed up in my home? They’re mostly black with red-orange lines on their backs, about ½ inch long. There aren’t many bugs still active outside at this time of year so where did they come from? Y. M. Merrimack, NH

Boxelder Bugs are Fall-invading Insects

Hard to answer this without seeing the insects, but at this time of year I think you may be looking at boxelder bugs that have moved inside looking for a place to spend the winter. Boxelder bugs, Boisea trivittata,  are outdoor plant-feeding insects that are rarely noticed until they end up in our homes (see Boxelder Bugs Are Overwintering Pests).

Boxelder bugs feed on the leaves and seed pods of the female boxelder tree. If you don’t have such a tree on your property, or on your neighbor’s property, you might never see a boxelder bug. But if you have a boxelder tree, you will probably be visited by boxelder bugs eventually.

When the weather cools in the fall, the adult bugs leave the foliage and congregate together at the base of the tree or on sunny foundation walls prior to moving into a winter site. If they can find openings around windows, vents, the roofline, etc., they will move indoors. They may then wander around for a while inside, particularly if the fall weather remains warm, but they will finally find a place to hide for the winter. They often end up in attics or in wall voids or ceiling voids.

Expect to See Them Indoors Again in the Spring

Once boxelder bugs are inside, control can be difficult since they are often scattered and hidden. You will probably see them again in spring as they “wake up” and look for a way to get back outside. They sometimes make a confused appearance on unusually warm winter days. At this time they are sluggish and can be vacuumed up, but avoid crushing them since they can give off a foul defensive odor.

The best control for repeat problems with boxelder bugs is to remove female boxelder trees, if possible. The trees are not high value and are usually not missed. Other options are to spray the tree foliage in summer or to treat around the perimeter of your home in early fall before the bugs congregate and move inside. If you give us a call at Colonial Pest, we can set you up with a protective program for next year. We can also “pest-proof” your home ahead of time, searching out and sealing openings that the bugs are using to get inside.

Photo Credit : William M. Ciesla, Forest Health Management International