What Causes Ladybugs to Come in a House?

There are over 5000 species of ladybugs, ladybirds or lady beetles. One of these species, Harmonia axyridis or the Asian lady beetle, introduced to the United States during the 1960s to control aphids, can infest homes and become a nuisance. Members of this ladybug species do not damage a home's structure, but exude a foul odor and a yellow fluid before dying that may stain fabrics.

Hibernation

Drops in temperature trigger Asian lady beetles to search for hibernation sites. They begin looking on the first day over 64.4 degrees F after the temperature drops to near freezing, according to a 2001 study by members of the Ohio State University Integrated Pest Management Program.

In their native China, Korea, Japan and Russia, Asian lady beetles seek out hibernation spots in trees or rocks. In the United States, however, the most convenient places are buildings. Once they find a dry, warm, secluded place, they hibernate until spring.

Contrast

Asian ladybugs look for hibernation spots in the late afternoon. They search for areas that have a sharply defined shadow across a light-colored object, such as a wall, door or window frame. This shows that in the late afternoon, that particular area gets enough sunlight to help ladybugs survive hibernation. This instinct is so strong that any sharp color contrast attracts them, including dark window frames against a light-colored house. Such light and dark contrasts make buildings near woods especially attractive, note University of Kentucky entomologists.

Warm Winter Days

Asian lady beetle swarms find cracks and crevices in houses to hibernate, such as in attics or inside walls. Any warm day in winter will wake them from their hibernation. They fly or crawl into the house, especially if the house is well lit. Light attracts ladybugs; lamplight inside homes mimics sunshine. In their native environment, Asian lady beetles emerge from sleep in the outdoors. When they hibernate inside of buildings, however, the beetles swarm around to find a way to get outside. Vacuuming is one way to remove beetles that find their way into homes.

Prevention

If one or more sides of a home was covered in lady beetles last autumn, it will be again. Prevention from ladybugs begins in spring or summer before the beetles search for hibernation spots. Seal up any cracks in walls, doors or windows so that the beetles cannot get inside of the house. The Ohio State study results suggest that spraying outdoor walls in autumn with an appropriate pesticide may effectively control Asian ladybugs.

References

• University of Kentucky Entomology; Asian Lady Beetle Infestation of Structures; Michael F. Potter, et al.; June 2005
• Ohio State University; The Multicolored Asian Lady Beetle (Harmonia axyridis) as a Nuisance Pest in Households Throughout Ohio; Margaret F. Huelsman, et al.
• National Geographic: Ladybugs