For Release June 12, 2001

AGRI-VIEWS
by Chuck Otte, Geary County Extension Agent

I have been swamped, these past two weeks, with questions about little red or red and black bugs. Sometimes they are being found on the sides of houses. Sometimes homeowners are seeing them in their lawns and sometimes they are swarming on the trunks of trees. Most people calling with questions about these insects also report that there is a variety of sizes with the larger ones having more black on them. These are all boxelder bugs.

Boxelder bugs are in that order of insects where the young insects look very much like the adult insects. For those of you who wish to turn this into a natural history lesson, this is known as gradual metamorphosis. This is different than complete metamorphosis, which butterflies experience, where the life stage between the egg and the adult looks vastly different and then goes through a resting period before becoming an adult.

The black that you see on the back of an adult boxelder bug is primarily the outer wing covers. They young boxelder bugs, or nymphs, do not have wings. This allows the red of the insect’s body to be very visible. As the nymphs grow, they start to develop wings. With each molt, the nymph’s wings get bigger and more black is seen on the back. Any time that you find a swarm of boxelder bugs in the late spring and summer, you are likely to find many different sizes, or ages, of boxelder bugs.

They overwinter as an adult. The adults come out of hibernation, often from our homes, mate and lay eggs. Boxelder bugs have a piercing mouthpart that they use to feed on the sap of trees, grasses and weeds. While their name indicates a preference for boxelder trees, they will just as likely be found on any other maple species or a very wide range of other host plants. Even though their numbers can be quite high, they seldom do damage to the host plant.

Boxelder bugs, like many other pest species in that same insect order including squash bugs and chinch bugs, are favored by warm and dry weather. They had a banner year in 2000 and many homeowners were plagued by swarms of these critters all winter long. So it is not surprising that we are seeing a lot of boxelder bugs this spring. They don’t really like cold weather, and cold wet weather can greatly decrease their numbers.

When the weather turned off cool for several weeks, they started acting as if it were autumn. They’d swarm together in warm areas or where the sun was shining. This would often cause them to cluster on the sides of houses, on sunlit lawn areas or on the lower parts of tree trunks. The good news is that with warmer weather they may disperse and not be quite as obvious.

As I indicated, they are seldom a real threat to plants, but they can certainly be a nuisance to homeowners. Besides being well adapted to warm dry weather, these insects also show amazing resistance to residual insecticides. If you can get the insecticidal spray right on them, they are easy to kill. But the ones that come along tomorrow, will probably not be killed by the insecticide residue left behind.

Since you shouldn’t be spraying insecticides around your house and lawn every day, there is a better solution. Boxelder bugs are fairly easily killed by hot water with a little soap in it. Merely mixing hot tap water with a little soap and spraying it on the swarms will offer satisfactory control, and you can spray them every day if you so wish. On the other hand, the problem may diminish as the summer wears on anyway. And then we’ll get to deal with them again in the fall!

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