This is the second in a four-part series of entries addressing insects frequently seen indoors at this time of year when they seek shelter for hibernation during the colder months. This entry will introduce boxelder bugs in the genus Boisea.
At this time of year, people often encounter boxelder bugs in great numbers on trees, shrubs, or all too frequently on the exterior of their home. These insects go through simple or “incomplete” metamorphosis, and the nymphs are becoming adults just before cold temperatures set in. The winged adults are thus able to disperse to, and congregate in, sheltered niches insulated from the brutal winter weather.
There are two species of boxelder bugs in North America. East of the Rocky Mountains one finds the eastern boxelder bug, Boisea trivittata. West of the Continental Divide ranges the western boxelder bug, Boisea rubrolineata. Both species were formerly placed in the genus Leptocoris, and many older references used that name. They belong to the family Rhopalidae, collectively known as “scentless plant bugs,” owing to the usual lack of defensive scent glands like those possessed by other true bugs such as leaf-footed bugs (Coreidae) and stink bugs (Pentatomidae).
The bold red and gray color pattern of boxelder bugs suggests that they must have some form of defense against predators that they are advertising through those bright aposematic colors. Indeed, the eastern boxelder bug is known to produce compounds known as monoterpene hydrocarbons that have been shown to deter predation by green anole lizards (source at PubMed).
Boxelder bugs mostly constitute a cosmetic nuisance to homeowners, and they can be easily excluded from the interior of a residence. Make sure that the weatherstripping on doors reaches the floor, and mend any holes in the window screens. Do be careful of bringing the bugs in accidentally, as the stack of firewood out back makes a convenient cozy shelter for the hibernating masses, too.
Come next spring the boxelder bugs will disperse again to their favorite host plants. Despite their large numbers, they cause remarkably little damage as they feed on the seeds of boxelder, maple, and other trees. So, marvel at this spectacle of abundance and be tolerant. Maybe your neighbors will learn from your example as well.