Lady Beetles

Robert Bishop 
Frederick County Master Gardener Program

Asian lady beetles, also known as ladybugs or ladybird beetles are swarming again. They can be a real nuisance when the congregate in large numbers on your house and find their way inside. They are accidental invaders of our homes and do not feed on our food crumbs or reproduce indoors. I received 18 phone calls requesting help with ladybugs last week, with 8 of the calls occurring in one day alone. Some of the callers are alarmed, thinking they discovered something strange and unusual and expect me to call the "authorities "or the news media to alert the public about this phenomenon. The truth is, this happens at various locations every year in Frederick County and across the eastcoast and midwest, it is not unusual at all.

Lady beetles are beneficial insects, predators of the insect world. Their larva are insatiable as they grow into adult beetles. They love to feed on a common landscape pest, the aphid. The larva looks nothing like the adult beetle, it has an alligator like appearance, and lacks wings. A single lady beetle will eat about 5000 aphids during it’s lifetime. They kill far more pest insects than the more widely known ‘praying’ mantid. There are over 350 species of lady beetles in North America.

Both the lady beetle larva and adult cause no harm to humans or pets. They do not bite or sting, cause structural problems to our homes, infest food and clothing, or carry diseases. Lady beetles have no natural enemies which is due to a liquid substance they emit from their bodies that smells bad, which in turn makes them taste bad to any other insect, bird, or animal. Try picking one up and see if you can smell the odor it secretes.

The U.S. Department of Agriculture released Asian lady beetles a few times from 1978 to 1981 in an attempt to introduce them to the eastern United States.

They were intended to be a biological control for aphids, scale insects and the hemlock wooly adelgid.

Mostly the Asian species is the one which becomes a nuisance every fall when they look for places to hibernate. Normally they live in trees and shrubs, but as winter approaches they fly above the trees in search of sheltered places to over winter together. Homes and buildings that are surrounded by trees and woods have more problems with large masses of beetles than those in more urban areas. The beetles are attracted to light colored buildings and even more to bright light and that is why they tend to congregate on the sunny side of structures. To attract each other to an ideal site they secrete a chemical known as "aggregating pheromone". The pheromone is like a chemical map leading them in and building up their numbers.

Once the group forms the beetles begin to look for shelter and that is why they enter buildings. They will go to any side of a building now, not only the sunny side. They can be found in the cracks of foundations, under roof shingles, around window and door frames, in wood piles, under siding or soffits, in attics or light fixtures, fan vents and other safe places. As winter ends the beetles slowly emerge on warm days and congregate once again to mate, then fly off to trees and shrubs to lays eggs and resume feeding. This mating period is usually interrupted at night when temperatures drop. After a week or two most of the beetles have emerged, mated and moved back to the trees and shrubs.

The best way to deal with this usually beneficial insect when it masses and becomes a problem is to deny entry. Check all your windows and doors and caulk to fill any gaps, cover exterior vents with plastic window screening, seal utility openings, repair window screens, install weather-stripping and door sweeps. The use of pesticide indoors is NOT recommended, instead sweep or vacuum them up when you find them in your home.

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