Last Friday, Larry Parker (Cincinnati Parks) sent to me the images below of Boxelder Bugs (Boisea trivittata, order Hemiptera) hanging out on a park building. 'Tis the season.
These boxelder bugs didn't fly to the building this spring; they were already there. This fall home invader overwintered somewhere in the building (walls, attic, etc.) and spring temperatures are beginning to roust them from their winter barracks. The bugs were clustered as they awaited outdoor temperatures that will support their flight; they were gone from the building as of yesterday.
The bugs Larry photographed had successfully made their way outside, but this is not always the case. Occasionally, they become confused by warm indoor temperatures and find their way into homes and other structures. They don’t bite or represent a threat to anyone or anything inside a structure, but they can be serious nuisance pest as they frantically crawl or fly around looking for a route to the great outdoors.
This is the first report I've received this spring of boxelder bugs emerging from their overwintering sites. However, with the predicted warm-up this week, I'm sure this is just the beginning.
We can also expect other fall home invaders to soon make their spring appearances. These include Western Conifer Seed Bugs (Leptoglossus occidentalis); Multicolored Asian Lady Beetles (Harmonia axyridis); and the notorious Brown Marmorated Stink Bugs (Halyomorpha halys).
Boxelder bugs range in size from 1/2" - 3/4" long. They are narrow-shaped, flat-backed, and dark gray or dark brownish-black. They have three highly visible orangish-red stripes running lengthwise on the pronotum, the area behind the head; "trivittata" is Latin for "three-striped".
The bugs are seed-feeders and are so-named because of a strong association with Acer negundo; however, both the adults and nymphs will commonly use their piercing-sucking mouthparts to draw juices from the seeds of other trees in the Acer genus. They have also been observed feeding on alder, apple, buckeye, cactus, geranium, grape, honeysuckle, lilac, linden, oak, peach, plum, spirea, strawberry, and tulip. I'm aware of boxelder trees being cut down in an attempt to eliminate the bugs; however, their wide-ranging feeding activity illustrates why this management effort may fail.
The best offense against these and other fall home invaders buzzing or lumbering around inside homes and other structures is a strong defense. Large openings created by the loss of old caulking around window frames or door jams provide easy access into homes. Such openings should be sealed using a good quality flexible caulk.
Poorly attached home siding and rips in window screens also provide an open invitation. The same is true of worn-out exterior door sweeps including doors leading into attached garages; they may as well have an "enter here" sign hanging on them. Venture into the attic to look for unprotected vents, such as bathroom and kitchen vents, or unscreened attic vents. While in the attic, look for openings around soffits. Both lady beetles and stink bugs commonly crawl upwards when they land on outside walls; gaps created by loose-fitting soffits are gateways into home attics.