Utah Pests News Fall 2007

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Boxelder Bugs Making the Move Again


Boxelder bugs are generally considered nuisance pests in Utah. They go relatively unnoticed most of the year, except when they start invading houses and other structures in large numbers during the fall. The good news is boxelder bugs are essentially harmless to plants and animals, and are not a serious problem every year (with a few exceptions; see page 7). But the bad news is they can stain fabrics and other surfaces, and are most abundant following hot, dry summers. So expect these insects to be a problem this year if you haven’t already encountered them in your office or home. 

Adult boxelder bugs are about ½-inch long, and are easily identified by their black and red wings that cross over the back, bulging red eyes, and obvious black antennae. Newly hatched nymphs are bright red and about 1/16-inch long; eventually nymphs will be more red and black with every molt until they reach the adult stage. Nymphs and adults have piercing sucking mouthparts and prefer to feed on the leaves, flowers, and seed pods of female boxelder, maple, or ash trees. Large numbers will congregate on pod-bearing trees; however, boxelder bugs will occasionally feed on male trees.

Some homes and other buildings seem especially attractive to boxelder bugs. Of course having female boxelder trees does increase the likelihood of having adults massing on buildings during the fall. The color, size, and shape of the structure may not be as important as the amount of sun exposure; adults tend to accumulate on southern or western parts of a building. The adults are the overwintering stage and try to squeeze into cracks until spring. Sometimes they work themselves into the building interior and actively look for an escape.

Insecticides are generally not recommended for boxelder bug control because they are not completely effective or long-lasting. There are several registered products for serious outbreaks in Utah (acephate, bifenthrin, carbaryl, deltamethrin, malathion, and permethrin). Professional pest controllers should be considered when treating large trees. Unfortunately, removing female trees will not prevent these nuisance insects because they are highly mobile. Periodically washing bugs off trees and buildings with soapy water will help reduce large numbers and minimize fall migration. Simply vacuuming nymphs and adults around window sills, furniture, and floors will prevent permanent fabric staining.

For more information, click here to see the UTAH PESTS boxelder bug fact sheet.

-Erin Hodgson, Extension Entomologist