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Boxelder bugs may invade buildings, especially during the warm days of spring and autumn, to seek shelter sites. They are attracted to lights and will readily fly in open doors and windows. Indoors, these bugs are a nuisance by their presence, produce a foul odor when crushed and may stain curtains with fecal matter. Outdoors, they can be found clustering in large numbers on the sides of trees, buildings and other structures. Large populations are often correlated with long, hot, dry summers. During warm winters and spring days, they may become active, moving from their hiding places into living spaces. Although they do not cause damage to buildings, clothing, food or humans, populations are annoying.
Adult boxelder bugs are flat-backed, elongate, narrow, about 1/2 inch long, 1/3 inch wide and dark brownish-black with three lengthwise red stripes behind the head. There are red veins in the wings and the abdomen is bright red under the wings. The nymphs or immatures resemble the adults in shape except they are smaller, more rounded, wingless and bright red.
Over wintering, adults leave their hibernating quarters with the coming of warm weather and females begin laying eggs (late April to early May) in crevices of tree bark, stones, leaves, grasses and on other objects near host plants. Eggs hatch in 11 to 19 days, with bright-red nymphs appearing about the same time new tree leaves develop. In July, new adults lay eggs that result in a second generation by early autumn.
Controlling boxelder bugs can be challenging. Removal of female boxelder trees would eliminate nuisance populations, as well as eliminating potential hiding places such as piles of boards, rocks, leaves, grass and other debris close to the house. Rake leaves and grass away from the foundation in a six- to ten-foot-wide strip, especially on the south and west sides of the structure. Be sure to caulk and close openings where boxelder bugs can enter the house such as around light fixtures, doors and windows, unscreened vents, holes in walls around utility pipes or conduits, air conditioners, heat pump lines and through the foundation.
These bugs are also attracted to lights and can fly in open doors or windows. Screen all windows, doors, crawl spaces, exhaust and roof vents and louvers. Clusters of bugs may be killed by pouring boiling water on them. Be careful to avoid killing grass and other desirable plants with boiling water. If boxelder tree removal is impractical, treat the young, exposed boxelder bugs "nymphs" on the trees during spring and early summer to prevent potential large populations and indoor migrations in the autumn. Applications of acephate (Orthene), carbaryl (Sevin) or chlorpyrifos (Dursban) sprayed to tree trunks, limbs and foliage are effective. Sprays can be applied on foundation walls, sidewalks, fence rows, etc. as boxelder bugs mature and migrate from the trees. Cracks and crevices, wall voids and similar areas may be treated with dusts and/or aerosols.