Boxelder bugs complete their fall stampede

Your house is the perfect spot for boxelder bugs to spend winter. Consider these management tips.

Boxelder bug adults and nymphs. Photo: James B. Hanson, USDA Forest Service,
Boxelder bug adults and nymphs. Photo: James B. Hanson, USDA Forest Service,

As the season changes and fall brings coloring leaves and warm days followed by cold nights, boxelder bugs and other insects that overwinter as adults begin their fall pilgrimage. Michigan State University Extension receives many calls this time of year about insects on windows and sides of houses, or strange piles of insects trying to come indoors. Generally, people are more concerned about groups of insects rather than one or two. However, when they are gathered on the side of the house or all over a window, concern turns to deeply worried. Right now, many trees, especially boxelder trees, have piles of red and black boxelder bugs collecting on trunks.

Juvenile boxelder bugs, called nymphs, are cherry red in color. As they grow larger, more and more black appears on their backs. Eventually, their backs are black, dark gray or deep brown with red along the wing edges and a few other areas. Juveniles of all sizes and adults will gather on the trunks of boxelder trees and others as the cycle of warm, sunny days and cold nights happen. This could be in late September, but most likely it is in October.

The shortening days and temperatures signal the time to seek winter shelter. Boxelder bugs and other overwintering insects are looking for winter lodging where the temperatures will stay comfortably between 40 and 50 degrees Fahrenheit. This is warm enough to hibernate, but cool enough that they don’t expend all their stored energy and die during winter. Only the adults store enough energy to make it through winter; all those little, red nymphs cannot survive winter.

Boxelder bugs are considered true bugs or Hemiptera. They are sucking insects. They feed on the flowers of boxelder trees in spring and a few other leaves and flowers along the way, but no one notices or even finds their damage. Boxelder bugs do not have any effect on crops or pets.

If they get indoors and get swatted or smashed, they leave a red stain, therefore it’s best to vacuum them up rather than squish them. Removing boxelder bugs when found by hand-picking or vacuuming works much better than using pesticides. Often, pesticides are ineffective on insects getting ready to go into hibernation.

Cutting down boxelder trees may do little to control yearly fall boxelder bug invasions. This is a prolific tree and if there is one in an area, there are dozens. Caulking, sealing and closing cracks will do more to limit numbers than any pesticide.

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