The Purdue Plant and Pest Diagnostic Laboratory

Asian Lady Bugs

Question: I know lady bugs are supposed to be good, but in our house in Maine this fall we had hundreds of them in the house and on the side of the house. Why in the Fall?

Asian Lady BeetlesAnswer: The following information was adapted from an article by Dan Suomi, an entomologist with the Washington State Department of Agriculture (Down the Garden Path Newsletter, April 14, 1994 #60).

The species found so abundantly is the multicolored Asian lady beetle, Harmonia axyridis, common in Japan, Korea and other parts of Asia. The name "multicolored" refers to tremendous color variation in this species, ranging from black with two red spots, to red with 19 black spots, and about every combination in between. They were introduced by USDA Agricultural Research scientists in the late 1970's and early 1980's as a biological control agent for pear psylla and other soft bodied insects.

In their native home, Harmonia axyridis overwinters in cliffs, but in the United States, unfortunately, the next best thing is a house. Attracted to vertical surfaces, they often appear on light-colored walls with a south-southwest exposure. These 1/4" long insects enter wall voids through cracks and settle down for the winter. With lengthening daylight, a warm interior often draws them inside. Residents become frustrated because daily vacuuming does not seem to rid the structure of beetles.

Lady beetles are beneficial insects and should be preserved, if possible. Locating entry points and sealing up cracks and crevices will help reduce their numbers inside homes. Make certain that screens and doors are tight-fitting. Concentrate initial efforts on the south and west sides of infested structures. Each day, dispose of vacuumed up beetles well away from the building, as these insects are strong fliers and will readily return. A wet-dry vacuum works quite well for this. Vacuuming the clusters from walls during fall may also offer some relief.

For more information refer to publication E-214 Asian Lady Beetles (PDF 32K). (NOTE: This requires Adobe Reader.)


Information listed is valid only for the state of Indiana.

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