By Faye Mahaffey
OSU Extension
Brown County Master Gardener Volunteer

They’re back! The last warm day that we enjoyed (before the frigid days leading up to St. Patrick’s Day) I noticed large clusters of Boxelder bugs sunning themselves on the side of our barn. What are they?

According to an OSUE Fact Sheet, Adult Boxelder bugs are flat-backed, elongated, narrow-bodied insects, about ½ inch long and 1/3 inch wide. They are dark brownish-black with three lengthwise red stripes on the pronotum (area behind the head) and reddish margins on the front wings; the abdomen is bright red underneath the wings.

As is characteristic of this order of insects (Heteroptera), the forewings are thick and leathery at the base, and membranous at the tip; the hindwings are entirely membranous. The head is black with a reddish-orange “beak” or proboscis. It has thin, four-segmented antennae that are half as long as the body. The nymphs or immatures resemble the adults in shape, but they are smaller, more rounded, wingless, and bright red. Eggs are dark reddish-brown.

Boxelder bugs are so named because they are a major pest of Boxelder trees, their primary host. These bugs feed on seed-bearing (female) Boxelder trees, and they also feed on seed-bearing silver maples; they do not feed on male trees. They use their piercing-sucking mouthparts to suck sap from the leaves, tender twigs, and developing seeds of host trees. Occasionally, they have been observed feeding on plum and apple fruits, causing some scarring or dimpling.

During autumn, adult and late-stage nymphs become gregarious and begin to congregate in large numbers, primarily on the bark of Boxelder trees. In my case, it is the outside of my hot tub! They then begin migrating by flying or crawling to protected overwintering sites. These bugs hide in cracks and crevices in walls, in door and window casings, around foundations, in stone piles, in tree holes, and in other protected places. Only full-grown adults overwinter. On warm days during winter and early spring, the bugs sometime emerge on light-colored surfaces outdoors on the south and west sides of houses and buildings, resting in the sun.

Indoors, these bugs are a nuisance because of their presence, and foul odor when crushed or disturbed. Although they do not cause damage to buildings, clothing, food, or humans, their presence is annoying. Outdoors, Boxelder bugs have the habit of clustering in large numbers on the sides of trees, buildings, and other structures. While Boxelder bugs have piercing-sucking mouthparts, they are not known to bite humans or animals.

Control Measures that are recommended by this Fact Sheet include: Prevention – Eliminate potential hiding places for the bugs such as piles of boards, rocks, leaves, grass, and other debris close to the house. Be sure to caulk and close openings where bugs can enter the house.
Non-Chemical Control Measures – Boiling water can be poured on clusters of bugs to kill them, but be careful to avoid killing grass and other desirable plants. Use caution on vinyl siding that could be damaged by the heat. Insects also can be vacuumed if the bag is then discarded.
Insecticides – The best time to treat young, exposed Boxelder bug nymphs on host trees is during spring and early summer to prevent potential large populations and indoor migration during the autumn. Many insecticides registered for “creeping and crawling” pests or “bugs” will work to quickly knock down these nuisance bugs. Be sure to read the label carefully and follow all instructions!

Interested in learning more about Pawpaw trees? Mark your calendars for the April 20 garden seminar being held at the Mt. Orab Campus of Southern State Community College at 7 p.m. in Room 107. All seminars are free and open to the public. Ron Powell will present the program, Pawpaw 101: Just the Basics. Subtopics will include history, cultivation, cultivars, marketing, nutrition, uses, and other items of interest pertaining to the North American Pawpaw.