The species found so abundantly is the multicolored Asian lady beetle, Harmonia axyridis, common in Japan, Korea and other parts of Asia. "Multicolored" refers to the tremendous color variations in this species, ranging from black with two red spots, to orange with 19 black spots, with every combination in between. This species was 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.
Numerous releases occurred in the United States; high populations have been reported in Washington, Oregon, Georgia and Virginia. Releases in Washington State were in Chelan, Klickitat and Yakima Counties, all east of the Cascade Mountains. The insects apparently did not establish in eastern Washington, but chose to relocate in western Washington. Others may have arrived here as unintentional passengers aboard cargo ships from the Orient.
Introduced insects often require 7 to 10 years to become established, thus the reason we are only now witnessing observable numbers. Being a recent import few natural enemies are available to keep Harmonia axyridis populations in check. This will necessitate management efforts by homeowners until the beetle population experiences a natural reduction.
Most lady beetle adults spend the winter months in clusters, protected from the weather. In their native home, Harmonia axyridis overwinters in cliffs, but in Washington, unfortunately, the next best thing is a house. Attracted to vertical surfaces, they often appear on light-colored walls with a south or 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 which can be frustrating to human residents.
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 indoors. Window screens and doors should be tight-fitting. Concentrate initial efforts on the south and west sides of infested structures. Each day, vacuum and dispose the 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. If entry points are still available, there may seem to be little reduction as new beetles enter. Vacuuming the clusters from walls during fall may also offer some relief.
Insecticides are not recommended as lady beetle carcasses will remain in wall voids where other insects, such as carpet beetles, will eat them. Upon depletion of this food source, the carpet beetles move readily into the home and feed on carpets, clothes, linens, stored food products, and many other items. Carpet beetles are extremely difficult to eliminate from a building.
Lady beetles eventually move outside to locate their natural prey in late spring. They do not feed on structural wood or stored food products. They do produce an offensive odor for repelling predators, but it does not affect humans. It has been recently discovered that a very few people are allergic to lady beetles ("Allergic rhinoconjunctivitis caused by Harmonia axyridis (Asian lady beetle, Japanese lady beetle or lady bug)." J Allergy Clin Immunol 1999;104: 704-705.) and having large numbers in the house may add to asthma problems.
In Georgia, pecan growers deliberately spread Harmonia axyridis larvae and adults in the orchards to control aphids, thus greatly reducing reliance on insecticides. In our area, we might see a decline in aphid, mite and scale insects infesting ornamental trees and shrubs. High numbers of lady beetles can result in reduced insecticide use, leading to an improved environment. Caulking and a few weeks of vacuuming may be a good investment for everyone.
For additional information, check out the University of Kentucky's excellent publication on H. axyridis and the North Carolina State University publication, "Multicolored Asian Lady Beetle Inside Houses". This one has plans for building a blacklight trap for capturing lady beetles that come indoors. Remember that pesticides mentioned in these publications may not be registered for home use in Washington State.
For more information contact your local WSU Extension Office.