Large numbers of lady beetles infesting homes and buildings in the United States were first reported in the early 1990s. Ladybugs are normally considered beneficial because they live outdoors and feed on plant pests.
However, one species of lady beetle (Harmonia axyridis) can be a nuisance as they fly to buildings in search of overwintering sites and end up indoors. Once inside they crawl about on windows and walls, often emitting a noxious odor and yellowish staining fluid before dying.
Where Did They Come From?
The Asian Lady Beetle, Harmonia axyridis (Pallas), is relatively new to this country. The beetle is native to Asia, where it dwells in trees and fields, preying on aphids and scale insects. The first field populations in the United States were found in Louisiana in 1988. Since then, the beetle has expanded its range to include much of the U.S. and parts of Canada. Earliest records in Kentucky date back to a few specimens collected in Hickman County in 1992.
Infestation Of Buildings
As autumn approaches, the adult beetles leave their summer feeding sites in yards, fields and forests for protected places to spend the winter. Unfortunately, homes and buildings are one such location. Swarms of lady beetles typically fly to buildings from September through November, depending on locale and weather conditions.
Lady beetles are attracted to sides of buildings receiving afternoon sun. Contrasting light-dark features are especially attractive. Studies have shown that Asian lady beetles are attracted to illuminated surfaces. They tend to congregate on the sunnier, southwest sides of buildings illuminated by afternoon sun. Homes or buildings shaded from afternoon sun are less likely to attract beetles. House color or type of construction (concrete, brick, wood/vinyl siding) is less of a factor for attraction than surface contrast.
Contrasting light-dark features tend to attract the beetles. Examples include dark shutters on a light background, light shutters on a dark background, windows edged with light-colored trim, gutters and downspouts on contrasting siding, etc. Dwellings near woods or fields are especially prone to infestation, although those in other locations can be infested as well.
Impact On Humans
Asian lady beetles generally do not injure humans and are mainly a nuisance. Unlike some household pests (e.g., fleas and cockroaches), they do not reproduce indoors—those appearing in late winter/early spring are the same individuals that entered the previous fall. Lady beetles do not attack wood, food or clothing. Nonetheless, some householders detest finding any insects indoors, and hygienic establishments such as hospitals have zero tolerance for contaminants of any kind.
People should avoid touching their eyes after handling the beetles, and should consult a physician if they suspect they are having an allergic reaction. When large numbers of beetles are flying in the fall, they often land on clothing and occasionally will bite or ‘pinch’ if in contact with skin. In nature, lady beetles eat other insects and have chewing mouthparts. The bite feels like a pinprick and is seldom serious.
Lady Beetle Management
People’s reaction to lady beetles varies widely from tolerance to revulsion. The following management tips are provided when the beetles become a serious nuisance within a dwelling.
Once the beetles are indoors, the easiest way to remove them is with a vacuum cleaner. If you later wish to release the beetles outdoors, place a handkerchief between the vacuum hose and the dust collection bag to act as a trap.
Sealing Entry Points
Sealing cracks and openings is the most permanent way of preventing lady beetles from entering buildings. The time to do this is in late spring or summer, before the adults begin flying to buildings in search of overwintering sites. Cracks should be sealed around windows, doors, soffits, fascia boards, utility pipes and wires, etc. with caulk or other suitable sealant.
Larger holes can be plugged with cement, urethane foam or copper mesh. Repair damaged window screens and install screening behind attic vents, which are common entry points. Install tight-fitting door sweeps or thresholds at the base of all exterior entry doors. Gaps of 1/8″ or less will permit entry of lady beetles and other insects. Gaps under sliding glass doors can be sealed with foam weather stripping.
These practices will also help prevent entry of flies, wasps, crickets, spiders and other pests. Some householders may find it more practical to hire a pest control firm, building contractor or painter to perform these services.
Insecticide foggers, “bug bombs” or sprays are generally not recommended for eliminating beetles indoors. Insecticides applied indoors for lady beetles tend to be ineffective and may stain or leave unwanted residues on walls, countertops and other surfaces. A vacuum is more sanitary and effective. Attempting to kill beetles hibernating in wall cavities and other protected locations is seldom effective. A better approach is to take preventive measures to reduce beetle entry in subsequent years.
Exterior Barrier Treatment
While sealing cracks and openings is a more permanent way to limit beetle entry, the approach is time-consuming and sometimes impractical. There can be countless cracks associated with eaves, siding, vents, etc. where insects can enter. On multi-story buildings, sealing becomes even more difficult. Fast-acting residual insecticides can be sprayed in a targeted band around windows, doors, eaves, soffits, attic vents, and other likely points of entry.
Some of the more effective insecticides used by professionals include Demand (lambda cyhalothrin), Suspend (deltamethrin), Talstar (bifenthrin) and Tempo (cyfluthrin). Effective over-the-counter versions of these products include Spectracide Triazicide, Bayer Advanced Powerforce Multi-Insect Killer, and Ortho Home Defense Max. Purchasing these products in concentrated (dilutable) form will allow larger volumes of material to be applied with a pump-up or hose-end sprayer.
To be effective, barrier treatments should be applied before the beetles enter buildings to overwinter. During late winter or early spring, barrier treatments are ineffective, as the beetles gained entry the previous autumn.