You may have noticed ½-inch-long black insects with red markings emerging from cracks and crevices inside or outside your home with the recent arrival of warmer weather. These are adult Boxelder Bugs that have been hibernating all winter and have become active with the warming days. They may disappear on days such as today when the weather turns cold again, but they’ll emerge for good in late April or May, just about the time buds on Boxelder trees are beginning to open.
During the spring and early summer they seek out and feed on low vegetation and seeds on the ground. Starting in mid‑July, they move to female seed-bearing Boxelder trees (or occasionally other maple or ash trees) where they lay eggs on trunks, branches, and leaves. Red nymphs hatch in roughly two weeks, and proceed, like their parents, to feed on Boxelder foliage and seeds by using their piercing-sucking mouthparts. Even if their numbers are large, there is no noticeable feeding injury to these trees. Come fall both adults and nymphs congregate in large numbers on the south side of trees, buildings and rocks exposed to the sun (only adults survive the winter) before settling in a protected hibernaculum. Boxelder Bugs are most abundant during hot, dry summers followed by warm springs. They do not bite people and are essentially harmless to property. (Photo: adult Boxelder Bugs in spring; insert – adults and nymphs in fall) Thanks to Jeannie Killam for photo op.
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