Farm Horizons, November 2009

Oodles of box elder bugs in 2010?

By Starrla Cray
Staff Writer

A warm home with a large, sunny exposure can be comforting come wintertime in Minnesota, but unfortunately, box elder bugs think so, too.

The orange and black insects typically search for a place to stay when temperatures drop in the fall, invading homes through crevices in siding, foundations, and windows.

“The thing that’s unusual this year is that we’ve had three cycles of reproduction,” said Matt Ferguson of Rainbow Pest Experts in Minnetonka. “On a typical year, you might see one or two. I think it’s due to the strange weather. It actually got warm the beginning of April, and just stayed that way.”

September was warmer than average as well, allowing the pests to stay active longer.

The food supply for box elder bugs is also up this fall. According to John Lloyd with the Urban Forestry Institute, the “helicopter” seeds from silver, Norway, sugar, and autumn blaze maples provide sustenance for the bugs. Their favorite is the seeds from box elder maple trees.

“There’s an excretion that the seeds give off, and box elder bugs feed on that,” Ferguson said.

With the dry weather this summer and fall, most maple trees are creating record crops of seeds as a survival strategy. This could mean an especially large number of box elder bugs next year when eggs hatch from the well-fed population of 2009.

Box elder bugs can often travel six blocks to a mile, Ferguson said. As a result, a home could have an infestation even if there are no maple trees on the property. In neighborhoods with a large number of maple trees, the box elder population is often higher.

Fortunately, the insects are not generally harmful and do not bite people. Their excrement does, however, stain curtains, furniture, and siding on buildings.

“The only damage they cause is if there are large numbers,” Ferguson said.

Box elder bugs mate in the spring, and in mid-July, they lay their eggs on the trunks, branches, and leaves of female box elder trees, according to the University of Minnesota Extension service.

The bugs start looking for a place to spend the winter on the second day of 60 degree or higher temperatures, after a frost, Ferguson said.

“I don’t know if that will happen this year or not,” he said. “It’s been so cool.”

Certain years are more conducive to large infestations of box elder bugs. They are most abundant when there is a warm spring followed by a hot, dry summer, according to the U of M extension web site.

In the fall, when they search for a winter hiding place, they are attracted to certain buildings. They prefer a southern or western exposure, and are often found on vinyl siding.

“They’re attracted to contrast – light and shade,” Ferguson explained. “Most siding is staggered, and the shadowed parts look like a crack to them.”

“I’ve literally seen it where you can barely see the siding because there are so many box elder bugs,” he added.

The bugs often crawl along the siding looking for an opening to crawl into, such as a crack in siding, windows, doors, or window screens. Caulking crevices and doing any necessary repairs can keep them from entering the building.

If there are box elder bugs indoors, they should not be squashed or vacuumed. According to Mike Misk of Rainbow Pest Experts, the insects create a bad odor when they are smashed.

One idea to get rid of them is to take a broom and knock them into a bucket of soapy water. Pest companies can also provide assistance.

Ferguson said a preventative, water-based insecticide can be applied to the exterior of buildings during the fall.

“When they touch it, it usually kills them in a little less than an hour,” he said.

If they have already landed on the building, there are products that can kill the insects within a few seconds.

“Usually they just fall right off, or they die and kind of cling to the siding,” Ferguson said.

Typically, box elder bugs go dormant in the winter, but when they enter a house, they stay active because of the heat.

“Any time they’re active, they’re going to feed, so they go around looking for food,” Ferguson said.

Box elder bugs throughout the years

Box elder bugs are not a serious problem every year, according to the U of M extension web site. They are most abundant during hot, dry summers when followed by warm springs.

They were very numerous in 1988, 1987, 1978, 1977, and 1975. They were also abundant in 1958, 1949, and the hot dry years of 1936 and 1935. (

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