The confusion between the native ladybug and the Multicolored Asian Lady Beetle (MALB, Harmonia axyridis) is common across North America. Both insects belong to the same family, Coccinellidae, and appear similar, but the MALB is an invasive species. It was deliberately introduced to control agricultural pests, particularly aphids, but its population has exploded. The MALB is now a significant household nuisance in the fall and winter months. Understanding a few distinct physical and behavioral traits makes telling the difference straightforward.
Identifying Key Physical Differences
The most reliable way to identify the Multicolored Asian Lady Beetle is by examining the pronotum, the plate directly behind its head. This segment on the MALB almost always features a distinct black marking shaped like an “M” or “W” against a white or cream background. Native ladybugs, such as the Seven-spotted Lady Beetle, typically lack this prominent marking. They usually have a mostly black pronotum with two small white spots on the sides instead.
Coloration and spot patterns also offer clues, though they are more variable. Native ladybugs tend to have a consistent, bright red or reddish-orange color with a predictable number of black spots. The MALB, however, has a wide variation in shell color, ranging from pale yellow or light orange to deep red. It can have anywhere from zero to 19 spots, living up to its “Multicolored” name.
The size and shape of the two beetles show subtle differences. The MALB is generally slightly larger than most native species, measuring about one-quarter inch long. It tends to have a more oval or slightly elongated body shape. Many native ladybugs are smaller and possess a more uniformly rounded, dome-like appearance.
Distinct Behavioral Differences
The most noticeable difference is their tendency to overwinter indoors. As temperatures drop in the fall, MALBs aggregate in large numbers on the sunniest, south-facing sides of structures. They seek warmth and entry points to hibernate inside. Native ladybugs rarely exhibit this behavior, preferring to overwinter outdoors in sheltered areas like leaf litter or beneath rocks.
The MALB is also known for a defensive behavior called reflex bleeding, a major source of homeowner complaints. When disturbed or crushed, the beetle secretes a foul-smelling, yellowish-orange fluid (hemolymph) from its leg joints. This fluid stains walls, furniture, and fabrics. This staining problem is rarely associated with native ladybugs.
Another behavioral distinction is the tendency for MALBs to “bite” humans when they land on skin. These are not true, painful bites, but the beetles may scrape the skin while searching for moisture or salts. This behavior is rarely seen in native ladybug species. This nuisance behavior, combined with the large number of invading beetles, explains why the MALB is considered a pest.
Management and Ecological Role
Both the native ladybug and the MALB are beneficial predators in the garden, consuming large quantities of agricultural pests like aphids. However, the MALB’s success has come at a cost to native populations. The invasive species competes for food and can even prey on the eggs and larvae of native ladybugs.
If you identify a native ladybug, the best course of action is to leave it alone or gently relocate it outdoors. This allows it to continue its role as a natural pest controller. Finding an MALB indoors requires a different approach, primarily due to the risk of staining.
It is advisable to avoid crushing the beetles to prevent the release of the staining hemolymph and odor. The most effective way to remove them from a home is by using a vacuum cleaner with a hose attachment. This allows for quick collection without crushing the insects. To prevent future infestations, sealing small cracks and entry points around windows and doors in the late summer and early fall is the most practical long-term strategy.