Asian Lady Beetles – From Beneficial Bug to Pest
While ladybugs are considered cute and pretty, the Asian lady beetle is anything but cute.
Overview of Asian Lady Beetles
Multicolored Asian lady beetles (Harmonia axyridis Pallas) were introduced into the United States from Asia to control crop pests between 1978 and 1981. They are now common throughout the United States. As predators of arthropod pests such as aphids, mites, thrips, scale and Lepidoptera eggs, they are considered beneficial most of the year. Unfortunately, as the weather gets cooler, the adults cluster in high numbers to overwinter and can become significant pests.
Asian lady beetles are usually recognized as typical ladybugs; however, they are slightly larger than native species. Coloration varies from a mustard-yellow to a dark reddish orange. Often, a number of spots are present on the wing covers, but in some specimens the spots are absent.
Where Asian Lady Beetles Appear
Colder weather and lack of prey triggers their flight to overwintering locations. They are attracted to light colored dwellings, and can enter homes and buildings through cracks, crevices and other small openings around windows, doors and roofs.
In the southern United States, this process peaks in October and November and can take a few weeks or more. As the beetles aggregate in the walls and other parts of dwelling, they may enter houses in large numbers. Inside walls, floors, attics and crawl spaces, they look for cool places to spend the winter. Sometimes this annoying movement can be heard from inside the house.
If the interior walls are warmer than they require for dormancy, they may exit into the interior of the home. It is not advised to use insecticides to kill them. Once inside, they fly around and land on walls, window coverings and furniture. When disturbed, Asian Lady Beetles produce a yellow viscous, foul-smelling defensive compound. They can also lightly bite but do not have venom.
How To Avoid Asian Lady Beetle Infestations:
- Make sure you have a tight seal around doors and windows.
- Use caulk to seal any cracks, crevices or holes in exterior walls.
- Use a black light sticky trap without an electronic zapper in rooms where the pests are observed as soon as they are seen.
- If Asian lady beetles gain access to a structure, they generally swarm in by the hundreds to overwinter in wall voids. It is not advised to use spray or dust insecticide into wall voids, because if they were to die in the wall void, it would cause a bad odor in the the home. Instead, allow them to emerge to the inside and outside of the home. They will usually die after a day.
- Be aware that use of a vacuum or other cleaning tools while they are alive will cause the beetles to produce a foul smelling defensive compound.
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