Question: My house has been invaded by lady beetles. They are coming out of the wall by the hundreds. Why are they here and what can I do about them?
Answer: Lady beetles are normally considered beneficial insects because they feed on pest insects such as aphids in gardens and landscapes. However, the multicolored Asian lady beetle (which is the one you have) can become a serious household problem. These beetles have been reported to congregate on the sides of buildings by the thousands. They will move inside if given the opportunity, and will stain carpeting, wallpaper, and anything else and they stink badly when crushed. However, these beetles are not poisonous, do not sting, are not carriers of disease, and do not eat wood.
The Asian lady beetle was originally released as a biological control agent for pecan aphids in California. They have a very wide host range and can feed on rose, apple, poplar, conifer, and crape myrtle aphids. Although they can be a nuisance overall they are quite beneficial.
The beetles seem to be attracted to light, reflective surfaces such as large windows, or light-colored walls and trim. Beetles usually are found on the sunniest areas of buildings. In Japan, Asian lady beetles overwinter in the cracks and crevices of mountain rocks. In the United States, they use buildings as protection from winter. They seem to be attracted to blue and gray colors that look like the mountainous rocks in their native habitat. The beetles begin to invade homes through cracks and crevices during the fall (around October or November in Alabama). People with log homes may find this beetle particularly troublesome due to the beetles' preference to dwell in cracks and crevices. Common overwintering sites include door and window frames, porches, underneath siding, roof shingles, wall voids, attics, and soffits.
This time of year, as the temperature increases, so will beetle activity. They have been in your home all winter and now are looking for a way out. As they try to escape, beetles can be found along large glass windows and in light fixtures because they are attracted to light, and around doors, baseboards, and drop ceilings.
Control involves a multi-pronged approach. Prevention is the key to keeping this lady beetle from getting into homes. A space less than 1/8 inch will allow lady beetles entry. To prevent entry you can use many of the same techniques that can save you energy as well: Caulk cracks along windows, doors, or other portals of entry. Seal and screen attic vents and install tight fitting door sweeps. Gaps under glass sliding doors may be sealed with foam weather stripping. Also, seal utility openings such as pipes, dryer vents, and cable TV wiring ports, with caulk, steel wool, or other mesh.
Once they are indoors chemicals are generally not recommended. The beetles have to be sprayed directly or walk over treated surfaces to obtain a toxic dose. Vacuuming or sweeping is the first line of defense. Do not crush the beetles as they can stain and they smell horrible. If you can empty the vacuum contents or sweepings outside some of the beetles may survive and pay you back by eating some of the bad bugs in your garden this summer.
Original photo by: Timothy J. Gibb, Extension Entomologist, Department of Entomology, Purdue University
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