The Asian ladybug, Harmonia axyridis, is a common sight, often recognized for its familiar dome-shaped body and varied coloration. While many associate ladybugs with beneficial roles in gardens, the presence of Asian ladybugs, particularly in large numbers, frequently raises questions about their potential negative impacts. These insects, originally from Asia, have become widespread, leading to increased interactions with humans and their property.
Identifying Asian Ladybugs
Identifying Asian ladybugs involves recognizing specific visual and behavioral cues that distinguish them from native species. These insects range in color from light orange to reddish-orange, with variations including yellow or mustard hues. Their wing covers may display a wide range of black spots, from none to as many as 22.
A distinct feature is the black ‘M’ or ‘W’ shaped marking on the white area behind their head, known as the pronotum. This marking reliably differentiates them from many native North American ladybugs. Asian ladybugs are also slightly larger than many native species, measuring about 1/4 inch (6 mm) long and 3/16 inch (5 mm) wide. They aggregate in large numbers, often on the sunny sides of buildings, and seek shelter indoors during colder months.
Harms to Humans and Property
Asian ladybugs can pose several nuisances to humans and property, moving beyond their beneficial role as predators. When disturbed or when food sources are scarce, they may bite. While these bites are not medically significant and do not transmit diseases, they can feel like a sharp pinch and may cause mild irritation or a small, raised red bump.
Their presence can also trigger allergic reactions in some individuals. Symptoms can include skin irritation, redness, itchy eyes, sneezing, and a runny or stuffy nose, similar to allergic rhinitis. More severe reactions, though rare, can affect the bronchial tubes, leading to asthma-like symptoms such as wheezing, shortness of breath, and chest tightness.
Asian ladybugs overwinter indoors, often forming large aggregations within homes. When disturbed, they release a yellowish, foul-smelling fluid through a process called reflex bleeding, a defensive mechanism. This fluid can stain walls, furniture, fabrics, and carpets, and its unpleasant odor can linger for extended periods.
Ecological Concerns
Beyond their direct impact on humans and property, Asian ladybugs raise broader ecological concerns due to their invasive nature. They compete with native ladybug species for resources, such as aphids and suitable overwintering sites. This competition can lead to a decline in native ladybug populations, as the Asian ladybug is hardier and more aggressive.
These insects also prey on the eggs and larvae of other beneficial insects, including native ladybugs. This aggressive predation further disrupts local ecosystems by reducing populations of other natural predators. In agricultural settings, Asian ladybugs can become a concern, particularly in fruit crops like grapes. They aggregate in grape clusters before harvest, and if accidentally processed with the fruit, the defensive chemicals they release can taint the flavor of wine or juice, leading to “ladybug taint.”
Managing Their Presence
Managing the presence of Asian ladybugs involves preventing their entry into structures and employing non-chemical removal methods when they appear. Sealing entry points is an effective preventative measure. This includes caulking cracks and openings around windows, doors, and foundations, repairing damaged screens, and proper weatherstripping. Sealing utility entry points and vents excludes them.
For indoor removal, non-chemical approaches are recommended to avoid staining and odors. Using a vacuum cleaner is an effective method; placing a nylon stocking over the hose before vacuuming can capture the beetles without crushing them, allowing for their release outdoors. Gently sweeping them into a dustpan is another option, though care should be taken not to crush them to prevent the release of their defensive fluid. Light traps can also attract and collect them, particularly in dark areas like attics. Chemical pesticides are not advised for indoor use, as they may be ineffective against overwintering insects in inaccessible areas and can pose health risks.