The insect often mistaken for a native ladybug is the multicolored Asian Lady Beetle, scientifically known as Harmonia axyridis. This species was intentionally introduced as a beneficial insect to control agricultural pests, but its tendency to swarm and enter buildings in the fall has made it a significant household nuisance. Confusion arises because of its similar domed body shape and vibrant coloration compared to native species. Its behavior and impact on homes and local ecology are vastly different from the beneficial native lady beetle.
Identifying the Asian Lady Beetle
The most reliable way to distinguish the multicolored Asian Lady Beetle from a native ladybug is to examine the pronotum, the area directly behind its head. This part of the beetle is typically white or cream-colored and features a distinct black marking shaped like an “M” or a “W.” The appearance of the letter depends on the viewing angle.
This beetle displays a wide range of physical appearances, explaining the “multicolored” part of its name. The color of the wing covers can range from pale yellow or orange to bright red, or even solid black in some forms. Spot counts are highly variable, with some individuals having no spots at all, while others may have as many as 19 distinct black spots. The adult is generally slightly larger and more oval-shaped than most native species, measuring about one-quarter to one-third of an inch in length.
Fall Aggregation and Defensive Behaviors
The Asian Lady Beetle becomes most noticeable in the autumn, particularly from mid-September through October, when it searches for sheltered overwintering sites. This behavior is called fall aggregation, where large groups gather on the exterior of structures. They are especially attracted to light-colored buildings and sun-exposed sides of houses, typically those facing south or southwest, as these areas provide the warmth they seek.
Once inside a home, the beetles can pose two primary nuisances. One is their tendency to “bite,” which is an exploratory attempt to find moisture or salt on the skin, often causing a slight pinch. The more significant issue is reflex bleeding, a defensive mechanism where the beetle exudes a foul-smelling, yellowish fluid called hemolymph from its leg joints when disturbed or crushed. This hemolymph contains alkaloids that can easily stain walls, fabrics, and furniture with a permanent yellow mark.
Origin and Ecological Status
The multicolored Asian Lady Beetle is native to eastern Asia, including Japan, China, and Siberia. It was first introduced to North America in the early 20th century, and repeatedly throughout the mid-to-late 1900s, as a biological control agent to manage agricultural pests such as aphids and scale insects. While it is an effective predator, it has since become established as an invasive species.
Its success as an invader is partly due to a superior competitive advantage over native lady beetles, primarily through a process known as intraguild predation. This involves the Asian Lady Beetle larvae and adults preying on the eggs and larvae of native species when food sources become scarce. The species also carries a microsporidian parasite that it is immune to, but which can be lethal to native lady beetles that consume the infected eggs or larvae. This combination of aggressive feeding and biological advantage has contributed to the decline of several native lady beetle populations.
Preventing Indoor Infestations
The most effective strategy for managing the Asian Lady Beetle is exclusion, which involves sealing all potential entry points into the home before the fall aggregation period begins. Homeowners should inspect the exterior of the house and use a good-quality caulk to seal cracks.
Exclusion Techniques
- Seal cracks around window frames, door casings, and utility line openings.
- Replace damaged window screens.
- Install weather stripping around doors and garage entries to eliminate small gaps.
If the beetles are already inside, the best method for removal is using a vacuum cleaner with a nylon stocking or fine filter placed over the end of the hose, secured with a rubber band. This technique captures the beetles without drawing them into the vacuum bag or canister. This prevents them from being crushed and releasing their staining hemolymph. The collected beetles can then be released outdoors away from the home, or simply disposed of.