Ladybugs, also called lady beetles or lady birds, are among our most beneficial insects. They are voracious and efficient predators of insect pests, and feed on more than 50 species of aphids. A single ladybug will consume thousands of pest insects in its lifetime, helping to protect home gardens as well as valuable commercial orchards and vegetable crops.
They don’t sting, transmit disease or infest food supplies, and of the more than 450 species of ladybugs in North America, only three feed on plants.
Yet one species, the multicoloured Asian lady beetle (Harmonia axyridis), has increasingly become a cause of complaints. That’s because they gather in large numbers in the fall, looking for a safe place to overwinter. Attracted to homes and buildings with sunny exposures, they will cluster on outside walls and, eventually, work their way indoors through cracks and openings. Their sheer numbers can make them a serious nuisance for some homeowners.
With their characteristic dome shape, orange-red bodies and black spots, ladybugs are among our most familiar insects. The main physical difference between the various species in Canada is the number of black spots on their wing covers, e.g., the two-spotted and thirteen-spotted lady beetles.
Multicoloured Asian lady beetles became established in North America after their introduction from eastern Asia in the 1970s to control aphids and other crop-eating insects. Their vigorous reproductive cycle and ability to withstand fairly harsh winters has helped them become a predominant species in Canada. They are slightly larger than native species, typically 6 to 10 mm long, and range in colour from a mustard yellow to a dark, reddish orange. They have a varying number of black spots on their wing covers, though some may have no spots. Also, the multicoloured Asian lady beetle has two white oval markings on either side of its head, and usually has an M-shaped marking just behind its head. As with many other insects, their bold colours are a defence, warning birds and other predators that they won't make a tasty meal.
Throughout the summer, ladybugs feed on softbodied insects, such as aphids and mealybugs. As fall nears and temperatures drop, most ladybug species prepare to overwinter on the forest floor, often at the base of trees, under bark, leaves or other debris.
The multicoloured Asian lady beetle, however, is attracted to sunny areas, including homes and buildings where they will congregate in the hundreds, even thousands, seeking warmth and a sheltered place to overwinter. Homes near fields or forested areas are particularly susceptible. After clustering on outside walls, many will work their way into the dwelling through gaps in doorframes and windowframes, eaves, utility openings, foundations and wall siding. Once inside, they become confused and gather on the walls, ceilings and around windows looking for an exit. Most of these stragglers die within a short time, but others may find a safe spot to hibernate in the attic or wall voids, emerging from time to time during mild weather.
A larger invasion can be expected for several days in the late winter or early spring, when they leave their winter hiding spots and try to move outdoors to mate. The multicoloured Asian lady beetle produces several generations each year: the adult females lay clusters of 10 to 50 tiny, light yellow eggs near aphid colonies. The larvae are spiny and mostly black with orange stripes, resembling tiny alligators, and these larvae share the adult's insatiable appetite for aphids.
Control of Multicoloured Asian Lady Beetles
Once multicoloured Asian lady beetles have moved in, there are few treatment options. The best method is to simply sweep or vacuum them up, then seal and discard the bag so they don’t escape back into the home.
Preventing multicoloured Asian lady beetles from entering buildings is the only method of control.
Exclusion techniques, including caulking and weatherstripping, can keep them outdoors where they belong. Focus on the sunny, southwest sides of the home, as shady areas are much less affected.
• Fix screens and caulk around windows and door jams.
• Seal any cracks and crevices in siding and the foundation.
• Plug holes in roofing, vents and attic walls.
• Inspect and seal gaps in service utility entrances.