Wednesday, September 30, 2009

Indoor Insects of Autumn (part 2 of 4)

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.


  1. These are the bugs that congregate on the south side of our house each fall. Around here we call them Democrat Bugs. I have no idea why, perhaps because they are as plentiful as Democrats?

  2. Hmm. . . Very interesting. I've definately seen these little guys around. What happens to the immature ones? Do they overwinter as well or are they not so lucky?

  3. The only boxelder bugs I've happened to see were in June, laying eggs on a Silver Maple leaf. Never even seen them in the house. It would be neat to stumble across one of these giant congregations of them.

  4. Shanda: The immature ones will reach adulthood before winter. At least most of them will. MoBugs, I've heard of that name (Democrat bugs) for them, too. Not sure why:-)

  5. Thanks for posting. I now know what's under the golden raintree.
    I also seem to have found an amelanistic one:

  6. Dan: Your pale specimen is "just molted," and the normal pigments have not yet expressed themselves. Further, those are not boxelder bugs. See this link re: Jadera:

  7. Thanks, Eric! I seem to have got it all wrong, but I wasn't too far off (still a bug), but it would be easier if they had their names written on their undersides. Do you happen to know the extent of damage they are capable of? The tree doesn't seem to be damaged, and I rather enjoy the bugs.

  8. Dan: You are correct that despite their abundance they seldom damage their host trees. Because of their sheer numbers they are often considered a "nuisance pest."


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