Behold, the Box Elder Bug

“You have bugs on your window,” a second grader said very quietly to me the other day, pointing at the windows behind me in our classroom.  I turned and looked, and she was right, the windows were crawling with red and black insects, but there were far fewer than there had been! 

Image from

Image from

Severson Dells is not alone when it comes to the annual invasion of box elder bugs (BEBs).  Members of the True Bug Family (Hemiptera), these stunningly colored black and red insects are the bane of many a home-owner when fall arrives.  Why are they here, what do they want, and why won’t they leave us alone?

Like with so many animals that have been labeled as “pests” in the eyes of humanity, our troubles with box elder bugs are ultimately our own fault.  Left to their own devices, they would be perfectly happy to leave us alone (see paragraph seven).

Box elder bugs, Boisea trivittata, are one of our native insects (bet you didn’t see that coming).  The family to which they belong, Rhopalidae, is known as the scentless plant bug family.  Its members are notorious for lacking the scent gland that is found on the hind legs of most true bugs.  However, unlike the rest of its kin, the BEB is not unscented.  In fact, it is apparently famous for its stink, which it produces only when pestered – no doubt it is part of its defense mechanism.  Biologists theorize that the production of this smell, and subsequent bad taste, is what allows BEBs to congregate in such large numbers in the fall without fear of being eaten.  The red and black coloring no doubt serves to advertise that it is not tasty, just like the coloration of ladybugs, milkweed bugs and monarch butterflies.

In the spring, the females lay their bright yellow eggs in the crevices of bark of the box elder tree.  The eggs turn red as the embryo develops, and within two weeks the youngster emerges.  Also red and black, just like its parents, the juvenile goes through several instars as a nymph before finally turning into an adult.  All the while, it is feeding on its host plant.  (Like aphids, BEBs have piercing and sucking mouthparts, designed to stab into the “flesh” of the plant on which they feed and suck out its juice.  The food of choice for BEBs is the seeds of the box elder tree, although they are also known to nip and sip from the tree’s leaves, flowers, and tender twigs.) 

So, summer arrives, the nymphs grow and eat, and eat and grow.  All good things must come to an end, however, and soon summer turns in to fall.  As the cooler weather approaches, the BEBs seek someplace new to live.  Remember I said that if left to their own devices, BEBs would happily not have any interactions with us?  It’s true.  In the wild, minus the presence of humans, these insects seek out rocks, loose bark, or hollow logs to crawl into or underneath for the winter.  If it is dry and sheltered, they will be happy.  People, however, have moved in to their habitats, and as we have altered the landscape, BEBs, like so many other animals, have had to adapt.  And lo! and behold – our houses provide dry, sheltered spaces that are just perfect for these insects to overwinter!  In they come – through cracks in the foundation, holes by utility wires or plumbing, old window screens.  They crawl under siding, and nestle by loose windows.  South- and west-facing walls are preferred real estate, for they get good and toasty on cool days when the sun is out.

BEBs are not going to hurt you and are not going to eat your wiring.  If your dog or cat tries to eat them, your pet may get sick, but I haven’t read of any accounts where a pet died after ingesting a BEB.  On the other hand, I have read that even though BEBs do not “bite people,” they have been known to inflict injury, although more as a defense mechanism (you rolled over on one in your sleep) than as a premeditated action (like a mosquito biting you for a blood meal).

So what is one to do when the BEBs seem like they are taking over one’s house?  Vacuum up the interlopers.  You could also employ a variety of sprays, from insecticides to mixtures of water and dish soap, but remember:  insecticides are poisons, and they are not often specific in their targets.  You are better off trying to prevent the insects from invading by plugging all possible entrances during the summer while they are out.  Replace old or torn screens; plug holes with tight wire mesh; put tight screens on foundation and attic vents; be liberal in your caulking adventures.

In the meantime, BEBs could make for some interesting insect studies.  Maybe you can capture and mark some – follow the daily lives of individuals.  Host BEB races for your friends and relatives.  Apply some engineering and see if you can build a better BEB trap!  Who knows – maybe you or your child might discover some previously unknown trait of BEBs that will change the world!