Ladybugs are widely recognized as beneficial insects, often associated with gardens and natural pest control. Many people appreciate these small beetles for their role in consuming common plant pests like aphids. However, the diverse family of ladybugs, known scientifically as Coccinellidae, includes thousands of species globally, and not all of them share the same beneficial characteristics. Some species can become problematic, particularly when introduced to new environments where they disrupt existing ecosystems and become household nuisances.
Identifying the Common Invasive Ladybug
The most commonly encountered problematic ladybug is the multicolored Asian lady beetle, Harmonia axyridis. This species typically measures between 5.5 and 8.5 mm in length, making it larger than many native ladybugs. Its body is generally oval and convex, with a smooth transition between its wing coverings, pronotum, and head. The coloration of these beetles is highly variable, ranging from pale yellow or orange to bright red, and they can have anywhere from zero to 22 black spots of varying sizes on their wing covers. Some forms are even uniformly black with two or four red markings.
A distinguishing feature of the multicolored Asian lady beetle is the pattern on its pronotum, the area directly behind its head. This area is often white or cream-colored and features black markings that frequently resemble an “M” or “W” shape, depending on the viewing angle. This characteristic mark, along with their larger size and oval shape, helps differentiate them from native species. The underside of the beetle is typically dark with a wide reddish-brown border.
Why This Ladybug Is Considered Problematic
The multicolored Asian lady beetle is considered problematic for several reasons. In the fall, these beetles tend to congregate in large numbers on the sunny sides of buildings, seeking sheltered locations to overwinter indoors. This mass invasion creates a nuisance for homeowners, as beetles enter homes through small openings. Once inside, they may crawl and fly about, especially during warmer periods in winter and early spring.
When disturbed, these beetles can emit a foul-smelling, yellowish fluid from their leg joints, known as reflex bleeding. This fluid contains defensive chemicals, including isopropyl methoxy pyrazine, which can stain porous surfaces like walls, furniture, and fabrics. Some individuals may also experience allergic reactions, such as allergic rhinoconjunctivitis, when exposed to these beetles or their secretions. While their bites are not typically serious, the beetles may bite humans, causing minor irritation.
Beyond household disturbances, the multicolored Asian lady beetle poses ecological concerns. It is a highly invasive species that can negatively impact native ladybug populations. This impact occurs through competition for food sources like aphids and intraguild predation on native ladybug eggs, larvae, and pupae. The multicolored Asian lady beetle can also carry a microsporidian parasite to which it is immune, but which can infect and harm other ladybug species.
Distinguishing Them from Native Ladybugs
Distinguishing the multicolored Asian lady beetle from native ladybugs is important for understanding their impact and managing their presence. While both types of beetles have rounded or oval bodies and can be red, orange, or yellow with black spots, certain features provide clear distinctions. Native ladybugs, such as the seven-spotted ladybug, often have a more consistent appearance, typically with seven spots and a black head with two small white spots.
In contrast to the distinct “M” or “W” on the multicolored Asian lady beetle’s pronotum, native ladybugs generally have different head and pronotum patterns. The convergent lady beetle, a common native species, is identified by two white lines that converge behind its head. Native ladybugs typically overwinter outdoors and do not aggregate indoors in large numbers.
Native ladybugs play a valuable role in ecosystems as natural pest control agents, consuming large quantities of aphids and other soft-bodied pests. A single ladybug can consume up to 50-60 aphids per day and thousands over its lifetime, reducing the need for chemical pesticides. Recognizing and protecting these beneficial native species is important for maintaining ecological balance in gardens and agricultural settings.