As our days grow cooler and our nights longer, insects emerge for their last hurrah before winter sets in. In wet years, we see an abundance of Asian lady beetles; in dry years, it’s boxelder bugs.

Boxelder bugs are "true bugs" and belong to the same family as stink bugs, cicadas and other insects with piercing and sucking mouthparts. They release a bad odor when crushed.

If you have suffered large swarms of these nuisance bugs in the past, and would like to get a jump on them before they get out of hand this year, here are some things you should know.

  • Boxelder bugs like warm areas and are attracted to buildings with a lot of southern or western exposure.
  • The best time to control them is in the fall and is most effective by sealing openings and the timely use of insecticides.
  • They normally do not cause property damage but they can potentially stain walls, curtains and other surfaces with their excrement.
  • You may find them around houseplants looking for water.

  • Once they are indoors, the only practical control is physical removal.

Adult boxelder bugs are about a half-inch long and are black with orange or red markings. Their wings lay flat over their bodies, overlapping each other to form an "X." Young boxelder bugs (nymphs) are one-sixteenth of an inch long. They are bright red when they first hatch, but change to red and black as they grow.

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The best way to manage boxelder bugs is prevention—keep them from entering your home from the start. This is done by sealing possible entry points around the home so they are unable to enter plus using an insecticide at the right time. Also:

  • Repair openings they can get into before the end of August.
  • Repair or replace damaged window and door screens.
  • Repair or replace damaged screens in roof and soffit vents, and in bathroom and kitchen fans.
  • Seal areas where cables, phone lines and other utility wires and pipes, outdoor faucets, dryer vents and other objects enter buildings.
  • Seal with caulk or, for larger spaces, use polyurethane expandable spray foam, copper mesh or another appropriate sealant.
  • Install door sweeps or thresholds to all exterior entry doors.
  • Install a rubber seal along the bottom of garage doors.
  • Use an insecticide on areas where bugs gather at doors and around windows.

Once boxelder bugs are found inside, the best option is to remove them with a vacuum or a broom and dust pan. It is not practical to try to treat wall voids and other hiding places to prevent them from emerging.

Since they don't live for very long, insecticides are not recommended once they have emerged into the inside of a home. When boxelder bugs are active, they do not live indoors more than a few days, and they don't reproduce inside.

When they come out in the spring, spraying insecticide does not prevent more from returning.

If large numbers of boxelder bugs are present or you have a history of boxelder bug invasions, you can supplement non-chemical control methods with an insecticide treatment around the outside of your home. The best time to spray is late summer and early fall when boxelder bugs are first clustering around the outside of buildings.

When choosing a product to use look under “Directions For Use” for information that says the product can be used on the exterior or outside of buildings. This information is often in small print.

You can find the common name for an insecticide by looking for “Active Ingredients” on the label. Common names of active ingredients available to the public include: bifenthrin, cyfluthrin, deltamethrin, lambda cyhalothrin, and permethrin.

For more information about boxelder bugs, visit: extension.umn.edu/nuisance-insects/boxelder-bugs.

Until next time, happy gardening!

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“By all these lovely tokens September days are here, With summer's best of weather And autumn's best of cheer.”

— Helen Hunt Jackson

Robin Trott is a horticulture educator with University of Minnesota Extension. Contact her at 320-762-3890, or at trot0053@umn.edu.