Beware the 'Death Spiral': Invasive Asian Lady Beetles Swarm Homes, Bite and Emit Foul Odor

As temperatures drop, homeowners across the United States are seeing an increase in invasive multicolored Asian lady beetles (Harmonia axyridis) seeking warm shelter for the winter. Often mistaken for native ladybugs, these beetles are notable for clustering in large numbers, occasionally biting when trapped against skin, and releasing a yellowish, foul-smelling fluid when disturbed.

Entomologists have dubbed one common behavior the "death spiral": tightly packed groups of beetles gather on sunlit walls and windows and spin as they attempt to enter buildings, sometimes exhausting themselves. Extension specialists report that sightings rise in October and can continue through the winter as the insects follow warmth and light and slip into homes through tiny gaps.

While they generally do not reproduce indoors or damage structural materials, these beetles can be a persistent nuisance. When crushed or alarmed they exude a defensive fluid from leg joints that has a strong, acrid odor and can stain fabrics, walls and upholstery. According to experts at the College of Agricultural, Consumer & Environmental Sciences at the University of Illinois, the beetles may bite if trapped between skin and clothing, but bites rarely break the skin. Ecologically, the species can also displace native ladybug populations by outcompeting them.

How they enter and where they gather

They are attracted to warm, sunlit surfaces and often cluster on the sunny sides of houses, near eaves, windows and around utility penetrations. Tiny openings around doors, window screens, foundations, pipes and chimneys are common entry points.

Prevention and removal

• Seal cracks and gaps around windows, doors, foundations, utility lines, chimneys and soffits with caulk or weatherstripping.
• Repair or replace damaged window screens and door sweeps; ensure siding and exterior trim are intact.
• Reduce indoor attraction by minimizing bright lights at night and closing curtains in rooms with many beetles on exterior walls.
• If beetles are already inside, vacuum them up rather than sweeping or squashing to avoid triggering the odor and stains; dispose of vacuum bags promptly.
• For large infestations or persistent problems, consult a licensed pest-management professional.

Scott Baker, an extension agent with the Virginia Cooperative Extension, notes that people often don't notice the insects during the growing season because they remain outdoors; the problem becomes apparent when they seek overwintering shelter. Homeowners can largely prevent disturbances by making homes less inviting and sealing common entry points before fall.

Sources: Virginia Cooperative Extension; College of Agricultural, Consumer & Environmental Sciences, University of Illinois.