By: Sandy Feather ©2009
Penn State Extension
Q. I have had ladybugs in my house before, and usually just catch the ones I see and put them outside. But this year the lady bugs have been unbelievable! Why so many, and do you have any better recommendations for getting rid of these lady beetles?
A. Growing conditions this summer resulted in lush plant growth that created a favorable environment for insects such as aphids to thrive. The high aphid population meant a plentiful food supply for multicolored Asian lady beetles (Harmonia axyridis), so their reproductive rate went up as well. Multicolored Asian lady beetles often become unwelcome invaders in homes as they look for sheltered locations to overwinter.
They usually begin massing on the sunniest sides of buildings after the first killing frost, looking for cracks and crevices to gain entry. In their native eastern Asia, they mass on south-facing cliffs where they push into rock crevices for shelter from winter cold. Overwintering lady beetles become active inside your house on sunny days in February and March, when they will congregate on windows and doors looking for a way out of your house.
These lady beetles were intentionally introduced into the United States as a biological control agent for aphids and scale insects. They were released in Pennsylvania in 1978 and 1981, but overwintering populations were not reported until 1993. It is thought that those releases failed to establish, and that the multicolored Asian lady beetles we have seen since 1993 were accidentally introduced in New Orleans from an Asian ship.
Although they do not sting, carry diseases or damage wood, fiber or foodstuffs, they can be annoying when they take up residence in large numbers. They do occasionally bite, and are equipped with a foul-smelling defensive chemical they emit when threatened or crushed that can stain surfaces. Some people report sinus irritation and mild dermatitis after handling the insects or after being exposed to large populations of them.
The best way to deal with these nuisance pests is to keep them out of your house as much as possible. Screen all openings and attic vents with number 20 or smaller mesh. Make sure your window screens do not have holes in them and that the weather-stripping on doors fits snugly. Caulk all cracks around window and doorframes, openings where utility pipes and wires enter your house, and any other opening to the outdoors.
You can reduce multicolored Asian lady beetle congregations outdoors with sprays of synthetic pyrethroids, including the active ingredients cyfluthrin, deltamethrin, lambda-cyhalothrin, sumithrin or tralomethrin. A licensed structural pest control operator should apply these products in late September or early October, just before insects begin to congregate. Since many pesticides are broken down by exposure to sunlight, the residual effect of such applications may not last more than a week.
Do not spray these products inside your home. They will not prevent insects from coming in through unsealed crevices. Also, even though these products may kill many insects in wall voids, their decaying bodies may attract carpet beetles that will damage wool fabrics, grain products of all kinds, pet food, and many other food items.
Use a vacuum to remove the beetles, and change the bag or empty the canister frequently. You can also trap them with black light traps that have sticky glue boards attached. These traps are available from pest control professionals and pest control supply companies. They are not the same as “bug zappers;” those should never be used inside your home. The sticky light traps are most effective at night when there are no competing light sources.
In addition to multicolored Asian lady beetle, other nuisance insects that take up residence for the winter include boxelder bugs, brown marmorated stink bugs and leaf-footed bugs. The same control options are recommended for them.