The Homeowners Column

The Homeowners Column

Nuisance Insects That Make Their Way Indoors in the Fall

Photo of Sandra Mason

Sandra Mason
Extension Educator, Horticulture
slmason@illinois.edu

This time of year every bug wants to be our roommate–lady bugs, boxelder bugs, elmleaf beetles and even flies. I'm sure I saw a couple of spiders eyeballing my backdoor, too. And if all the buggy creatures weren't enough, we also get mice nestling into the garage. They are all looking for a warm spot to spend the winter. In addition over the past couple of years we have seen an increase in the numbers of an imported ladybug called the Asian multicolored lady beetle. As fall approaches most of the insects make their way into our homes through cracks and crevices usually around windows or they may fly through doors as people go in and out. Insects may be brought indoors on houseplants after a summer vacation outdoors. Particularly on warm sunny days insects may be seen crawling or flying around windows.

The Asian lady beetles are one fourth inch long and are the VW bug dome shape. They usually have orange wingcovers with 19 black spots. No need to count the spots. Their multicolored name comes from the variety of color possibilities ranging from tan to red and the spots may be very small to absent to large and obvious.

In their native areas in Japan, the lady bugs spend the winter in cracks and crevices of cliffs. Cliffs are tough to find in central Illinois so what is the next best upright thing around – our homes of course. In the spring, they will return to the outside to lay eggs. Lady bugs are actually good bugs. Repeat this over and over to yourself as you are scooping them up from your window sills. Both the young larva and the adults feed on a wide range of soft-bodied and slow-moving insects such as aphids and young caterpillars. According to Phil Nixon, U of I entomologist, they also feed heavily on soft scale insects which is why they were imported into this county from Japan.

The larvae are quite science fiction looking. They look like tiny black alligators with an orange stripe. In the aphid size world they probably seem just as fierce.

Elm leaf beetles may act the same indoors as lady beetles, but outdoors they are not good guys. They feed heavily on the leaves of Siberian and American elm trees. Elm leaf beetles are one fourth inch long and are yellowish with a black stripe along the edge of each wing cover. Boxelder bugs are black with red stripes. They feed on the developing leaves, flowers and fruits of boxelders and other maples. In the fall, they crowd together on the south sides of trees or buildings exposed to the sun, then fly to nearby buildings to hibernate.

The good news is elm leaf beetles, boxelder bugs and ladybugs don't reproduce or feed while they are indoors but are a nuisance with their presence. Controlling these insects indoors consists of vacuuming or your best scoop and toss outside method.

According to Nixon, insecticide sprays are likely to have little effect on hard shelled insects that are not feeding. Caulking cracks and crevices around windows, along the foundation and around doors will help reduce the numbers indoors.

If you are still wrestling with mice, we have a great fact sheet that details mice and rat control options.

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