Lady Beetles in Your Home: When the Invited Guest becomes a Pest

asian lady beetle

Did you know that 50% of the people with lady beetles in the home have an allergic reaction? Did you know that the substance that they reflex-bleed can stain?  Discover what to do if you have to deal with a lady beetle invasion.

 

 

Most lady beetle species are beneficial to the environment as important agricultural biological controls. There are a few species from the subfamily Epilachninae that are notorious plant pests. But there is one species that is actually both beneficial AND a pest. . .not a pest by the agricultural definition of feeding on plant crops, but a nuisance in its overwintering behaviors.

Maybe Not an Official Pest but an Unofficial Nuisance

The Asian lady beetle, Harmonia axyridis, was introduced to the United States from Japan by the USDA in the 1970’s as a biological control against aphids. (Though many experts believe that their spread is due to an infestation that arrived from Japan by freighter). They have since spread to most of the US and parts of Canada. Though they are beneficial in this regards, it is their overwintering habits that make them a nuisance. Rather than overwinter under rocks and crevices or migrate to warmer surroundings like other lady beetles, they are attracted to the southwest sides of buildings that are heated by the sun. Once they have landed, they search for any entry to the structure.

Another habit of the species that makes this a much larger nuisance is that lady beetles in general like to hibernate in groups. When only a few aggregate and overwinter they normally go unnoticed, but often they will enter a dwelling as a swarm.

How Can I Identify an Asian Beetle?

Asian beetles have different markings and different colors, but they all have the same marking behind the head. You can identify this beetle from others by the ‘M’ shape on its pronotum, the plate-like structure at the dorsal surface of the thorax. (See photo above)

What Damage Do They Cause?

Staining: Swarms of insects can definitely be unnerving. Lady beetles in general share a defense mechanism that could become a problem inside of a home. When disturbed they release hemolymph (the blood and intestinal fluid of arthropods) from their leg joints. It contains toxins and has a repulsive smell. The issue with beetle home invasions is that the substance is yellow and will stain.

Human Allergen: Many experts are now reporting that ladybug allergies are on the rise. Never heard of it? Then you might be surprised to know that a recent study presented at the annual meeting of the American Academy of Allergy, Asthma, and Immunology, as many as 50% of people who experienced the Asian lady beetle home invasions reported being allergic. In a separate study, a second doctor concurred reporting that after reviewing the results of 1,400 skin prick tests, 21% tested positive for the allergy.

They Bite: If you have ever experienced it, you may have thought that you were stung by a lady beetle. In fact, you were bitten. But not as an act of aggression. Lady beetles have chewing mouthparts and will test out possible food sources. It is nothing more than a slight pinch that does not break the skin.

The Good News

Other than being a slight nuisance, lady beetles do not enter your home with the intentions of it serving as a food source. They don’t eat wood, drywall, or any other building material. They also don’t eat human food. In fact, when a lady beetle overwinters it enters a dormant state called diapause during which time they do not eat or reproduce. They are not known to carry diseases.

You may not even know that the beetles have aggregated in the walls of your home until they emerge in the spring looking for an escape so they can mate.

How to Keep Them Out

Discourage Loitering. They will first congregate on the exterior of your home looking for a way to gain entry. Use this opportunity to discourage them from choosing your house by hitting them with a blast from the hose or a leaf blower.

Exclude Them. Though swarms look impressive, keep in mind just how tiny each individual lady beetle is. They will crawl through any cracks such as those at doors and windows and those in the foundation. They will seek out vents as well as utility openings. In order to exclude them you must make the house air-tight prior to September. Use caulking, weather stripping, and door sweeps. Use insect screening around vents.

Kick Them to the Curb. They’ve gained entry! Now what? You will need to remove them, but because of their defense mechanisms, you will need to be cautious. Crushing them will result in staining. Vacuuming is the easiest and cleanest way to remove them. If you know where they are hibernating on a cold day, vacuum them up while they are dormant. Once captured you can release them away from your home.

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