BIG QUESTION COL Box invasion begins; numbers to increase

I'm starting to notice those red-and-black box elder bugs on my house. Can we expect a lot more of them?

The annual invasion of the box elder bugs has started, and the Asian lady beetles are just behind them.

When the nights cool off but days remain warm, the bugs start to congregate, often seeking out the south and west sides of houses, said Doug Courneya, a horticulturist in Olmsted County. In southeastern Minnesota, that occurs in late September and early October.

They often squeeze into cracks and openings in the house and end up inside, as they look for protected places for the winter, Courneya said.

Both bugs are harmless, although the Asian lady beetles do bite, he said. When the bugs gather in large numbers, their excrement can stain siding.


"They're just a nuisance," Courneya said.

During the summer, you don't notice box elder bugs because they're out feeding on trees, especially box elder trees, he said.

One way to get relief from them is to spray insecticide on the south and west sides of your house -- it usually lasts for 24 to 48 hours, he said.

Another way is to seal cracks with caulk so the bugs don't get inside.

Once the bugs get inside, however, Courneya doesn't recommend using pesticides on them. Light traps are available, as the bugs are attracted to light. Some people vacuum the bugs up.

Once inside, the bugs often creep into attic areas or cracks in the house. While some die, others go dormant. They'll become active again when the temperature warms up during winter, crawling out into the rooms.

The box elder bug population is cyclical, going up and down as its predator population fluctuates. This year looks like a big year, Courneya said.

For answers to horticulture questions, call the Olmsted County horticulture answer line at 529-6114.


-- Mike Klein

The Big Q is a weekly feature that provides background on issues in the news. To suggest topics for Big Q, e-mail with Big Q in the subject line, or call Assistant City Editor Mike Klein at 281-7481.

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