As seasons change, insects often gather indoors. The insects commonly found in large numbers are typically not native ladybugs but the multicolored Asian lady beetle, Harmonia axyridis.
Identifying the Culprit
While both are beneficial garden predators, the Asian lady beetle is known for becoming a household nuisance. You can differentiate them by several visual characteristics. Asian lady beetles often have a distinct “M” or “W” shaped black marking on the white area directly behind their head. Their coloration varies widely, from yellow or orange to red, and they may have many spots, few spots, or none at all on their wing covers. Native ladybugs are consistently bright red with black spots and lack the prominent “M” or “W” marking. Asian lady beetles are also slightly larger and more oval-shaped than their native counterparts.
Reasons for Indoor Presence
Asian lady beetles seek shelter indoors to overwinter as outdoor temperatures drop. Homes and other buildings offer ideal hibernation sites, mimicking the rock crevices and cliff faces they might use in their native Asian habitats. These beetles are attracted to light-colored buildings and the warmth of sun-exposed surfaces, especially those with western or southern exposure. Once a few beetles find a suitable entry point, they release aggregation pheromones, chemical signals that attract more of their kind to the same location. This pheromone can remain on the building, making it attractive to beetles in subsequent years. They often enter through tiny cracks and openings around windows, doors, utility pipes, and foundations, fitting through gaps as small as 1/8th of an inch.
Are They a Threat?
While Asian lady beetles can be a nuisance, they are not dangerous to humans or pets and do not carry diseases. They do not eat wood, fabric, or food items within the home, posing no threat to property. However, they can bite, causing minor, short-lived discomfort like a pinprick. When disturbed or crushed, Asian lady beetles exhibit “reflex bleeding,” releasing a foul-smelling, yellowish fluid from their leg joints. This fluid can stain surfaces like walls, furniture, and fabrics. Some individuals may experience allergic reactions, such as eye irritation or asthma-like symptoms, from exposure to these beetles or their secretions. If ingested by pets, their defensive compounds can cause irritation or stomach upset, though most pets dislike the taste.
Safe Removal Strategies
Once Asian lady beetles are inside your home, the most effective and least messy removal method is using a vacuum cleaner with a hose attachment. This prevents the beetles from releasing their defensive, foul-smelling fluid, which can stain surfaces. After vacuuming, immediately empty the vacuum bag or canister outdoors into a sealed bag or container to prevent escape or lingering odors. For smaller numbers, gently sweep them into a dustpan or use paper to usher them into a container. Avoid crushing the beetles, as this triggers reflex bleeding and causes staining. Light traps can also be effective in attracting and capturing them, particularly in darker areas like attics.
Preventing Future Invasions
The most effective long-term strategy for preventing Asian lady beetles from entering your home is to seal all potential entry points. This includes sealing cracks and openings around windows, doors, utility pipes, wires, and foundations with caulk or other suitable sealants. Larger holes can be plugged with materials like cement, urethane foam, or copper mesh. Repairing damaged window screens, attic vents, and ensuring proper weatherstripping around doors and windows are important steps. These efforts should be completed in late spring or summer, before the beetles begin their search for overwintering sites in the fall. Maintaining a tidy garden and avoiding leaving damaged fruit or plants can also reduce their outdoor attraction to your property.