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Lady Beetles Invading Your Home?

By Judy Sedbrook, Colorado Master GardenerSM, Colorado State University Cooperative Extension, Denver County

In recent years, a new species of lady beetle has become established in Colorado. Harmonia axyridis, or the multi-colored Asian lady beetle, was originally brought to the United States from China.  First introduced in 1916, it was reintroduced again in 1978 and 1981 to control aphids and scale insects affecting fruit and shade trees. The insect gets its name because of its variable spotting, and broad color range from yellow-orange to dark red. 

Although it appears to be an effective predator of many insects, the Asian lady beetle has an unfortunate habit of wandering into homes during late fall. Infestation usually begins with the beetles congregating on a sunny south or southwest facing wall. They then seek entry into the home through cracks and crevices to overwinter. In some parts of the United States this insect has become a number one nuisance among over-wintering invaders such as boxelder bugs and elm leaf beetles. The lady beetles do not reproduce within homes and, essentially, are harmless.

Their very presence with a home, however, can cause considerable concern. They may leave a messy smear and distinct foul odor if crushed. While most people are merely annoyed by this odor, some have reported having allergic (sinus and mild skin irritations) reactions when exposed to these defensive excretions. The beetles have also been known to bite exposed areas of the skin. These bites are harmless.

Control

The most efficient way of collecting the Asian lady beetle once they are in the home, is to remove by vacuuming.

Black (ultra-violet) light traps are another way of catching beetles that may be flying or crawling around the inside of homes. Beetles are collected on sticky glueboards that can be replaced when full. These traps can be purchased from pest control companies or can be assembled by the do-it-yourself homeowner. A pdf printable description of such a trap is available from the USDA describing the items necessary to build your own. Light traps are most effective at night when there are no competing light sources. DO NOT use so-called electric "bug-zappers" in the home.

Preventing the lady beetles from entering the home to begin with would seem to be the best method of control. Silicone or silicone-latex caulk should be used to seal cracks around windows, doors, siding, utility pipes, and other openings. Screens on windows and doors should be repaired or replaced. Openings into attics, chimneys and vents should be covered with a fine-mesh screen.

Exterior applications of insecticides may be beneficial when sealing entrances from the exterior of the home is not possible. Synthetic pyrethroids can be applied by a licensed pest control operator in the fall, just prior to beetle congregation. The benefits of such an application are limited, however, as the chemicals are quickly broken down by sunlight and may not last much more than a week.

New research has shown that the entry of the lady beetles into your home may also be prevented by use of vapor repellants. Researchers with the Chemicals Affecting Insect Behavior Laboratory in Beltsville, Md., found that both camphor and menthol vapors are an irritant to the beetle’s chemosensory organs. These organs, much like little taste buds, were found to be so sensitive that the vapors from either of the two compounds were enough to repel the lady beetles.

Photo: Judy Sedbrook

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Date last revised: 01/05/2010