The introduction of the Asian lady beetle (Harmonia axyridis) to North America for pest control has created confusion among homeowners and gardeners. Native ladybugs belong to the Coccinellidae family and are recognized as beneficial insects. Distinguishing between these two beetles is important, as one is a harmless garden ally while the other is an invasive species with nuisance behaviors.
Key Physical Differences for Identification
The most reliable visual difference is found on the pronotum, the shield-like segment behind the head. The Asian lady beetle possesses a distinct black mark on its white pronotum that resembles the letter “M” or “W,” depending on the viewing angle. Native ladybugs, in contrast, typically have a black pronotum with small, simple white patches on the sides, often referred to as “cheeks,” but they lack this prominent central marking.
Coloration and spot patterns vary significantly between the two species. While native ladybugs are often a consistent, bright red with a set number of spots, the Asian lady beetle is described as “multicolored” due to its wide range of shades, from pale yellow to dark orange or red. An Asian lady beetle can have anywhere from zero to 20 black spots, often appearing irregular. The Asian beetle tends to be slightly larger, measuring 5.5 to 8.5 millimeters, and has a more oval or elongated body shape compared to the smaller, dome-like native species.
Behavioral Traits and Ecological Impact
A primary difference between the two species is where they choose to spend the winter months. Native ladybugs overwinter outdoors, seeking shelter in natural spaces like under leaf litter, bark, or rocks. The Asian lady beetle, however, exhibits a strong tendency to aggregate in large numbers and seek refuge inside man-made structures, often attracted to the sunny, south-facing walls of homes during the fall.
The Asian lady beetle can become a nuisance because it is known to “nip” or bite humans when seeking moisture or warmth, a behavior native ladybugs rarely show. When disturbed or crushed, the Asian beetle releases a defensive, foul-smelling, yellowish-orange fluid from its leg joints. This fluid contains alkaloids and can leave permanent stains on interior surfaces, including walls, fabrics, and carpets. The invasive nature of Harmonia axyridis also causes an ecological impact, as it is a highly competitive predator that sometimes feeds on the larvae and eggs of native ladybug species.
Practical Management and Exclusion
Since native ladybugs are valuable predators of agricultural pests, any identified outdoors should be left alone. However, managing the Asian lady beetle focuses heavily on prevention and safe removal to avoid its indoor nuisance behaviors. The most effective long-term strategy is exclusion, which involves sealing all exterior entry points before the fall, when the beetles begin seeking overwintering sites.
Homeowners should caulk cracks around windows and door frames, repair any damaged window screens, and use fine mesh to cover vents and other openings. Once Asian lady beetles have found their way inside, crushing them must be avoided to prevent the release of the staining hemolymph. The best method for indoor removal is to use a vacuum cleaner, ideally by placing a nylon stocking inside the nozzle to gently trap the beetles for easy and clean disposal outside, preventing both the stain and the smell.