The native ladybug is a familiar sight in North American gardens. It is often confused with the Multicolored Asian Lady Beetle (Harmonia axyridis), an invasive species introduced to control agricultural pests. Both insects share a similar dome shape and feed on soft-bodied plant pests, leading to frequent misidentification. Distinguishing the two is important because the Asian Lady Beetle tends to overwinter indoors and has a variable appearance. The clearest way to tell them apart involves examining their physical features and distinct behaviors.
The Definitive Marker: Head and Thorax
The most reliable way to differentiate the Asian Lady Beetle (ALB) from a native ladybug is to inspect the pronotum, the area directly behind the head. On native ladybugs, this shield-like plate is typically black with two small white markings on the sides. This pattern gives the native insect a uniformly black head appearance with small white accents.
The Asian Lady Beetle, in contrast, has a distinct black marking on its light-colored pronotum. This marking is often described as an “M” or “W” shape. While the exact size and thickness of this black marking can vary, it is a consistent feature not present on native species. This pronounced black shape against the white or pale yellow background provides a definitive identification point, even when the insect’s wing covers are confusingly colored.
Spot Patterns and Color Variability
Native ladybug species generally maintain consistent color and spot counts, making them visually predictable. The Asian Lady Beetle, however, exhibits extreme color and pattern variability, which is why it is often called the Multicolored Asian Lady Beetle.
The wing covers (elytra) of the Asian Lady Beetle can range from pale yellow and orange to deep red and black. The spots on the ALB can number from zero to 19 or more, and they may be large, faded, or completely absent. Relying solely on the color or number of spots is an unreliable identification method. The ALB’s polymorphous nature can easily lead to its misidentification as several different species of native ladybugs.
Practical Differences in Behavior and Habitat
A significant difference between the species is the Asian Lady Beetle’s habit of forming large aggregations to overwinter, often choosing man-made structures. As temperatures drop in the late fall, ALBs swarm toward light-colored buildings and aggregate on sunny, south-facing sides. They then seek shelter inside wall voids and attics. Native ladybugs, conversely, typically seek sheltered locations outdoors, such as under leaf litter, bark, or rocks.
When disturbed or handled, the Asian Lady Beetle employs a defense mechanism called reflex bleeding. This involves secreting a yellowish-orange fluid (hemolymph containing a foul-smelling alkaloid) from its leg joints. This fluid can stain walls, fabrics, and furniture, and is a reaction not commonly observed in native species. The Asian Lady Beetle also has a greater tendency to bite humans when handled or provoked. These bites are usually a defensive pinch but can cause minor irritation.