Asian lady beetles in your Delaware house in October

How to identify them

Adults are domed, oval beetles about 1/4 inch long, in colors from beige and yellow-orange to bright red. The black spots may be many, few or none, so color and spots alone are an unreliable clue. The best one is the white patch just behind the head, which has a black “M” or “W” mark (it can be filled in and look like a dark patch on darker beetles).

Why Asian lady beetles come inside in fall

University of Delaware Cooperative Extension’s Kent County horticulture posts list the multicolored Asian lady beetle as a fall house invader, drawn to white or brightly colored buildings that resemble the light stone outcroppings of its native overwintering sites, and found on the south and west exposures of windows. We did not find a Delaware page with exact dates, so timing comes from nearby states: Penn State says overwintering behavior begins around the beginning of October, Minnesota puts the flights between late September and late October, and Ohio State says the move happens on the first day above 64°F after a sharp cold snap, usually mid- to late October there. The beetles gather on sunny walls, then crawl into gaps as small as 1/8 inch. Many stay hidden in wall voids and attics, and beetles that wander into heated rooms are usually doomed. They don’t reproduce indoors or damage wood, fabric or food, and mild winter days can wake them. Those that survive try to leave in spring.

When they’re active

What you can do now

• Vacuum them up. For a bagless vacuum, rubber-band a knee-high nylon stocking inside the hose so the beetles collect in it, then remove the stocking right away and tie it off. For a bagged vacuum, take the bag out after each use and tape and discard it or freeze it so the beetles can’t crawl back out.
• Don’t crush or swat them. They release a foul-smelling, yellowish fluid that can stain walls, drapes and carpet. Penn State notes that people who are allergic to these beetles may not be able to vacuum them, because the vacuum exhaust spreads the odor.
• Seal gaps with good silicone or silicone-latex caulk around windows, doors, siding and utility pipes, and fix torn screens. Cover attic vents and exhaust fans with fine screen (20-mesh or smaller) and add door sweeps. Start in the rooms where the beetles show up most.
• Find where they come out inside, usually under or behind baseboards, around window and door trim, and around ceiling lights and exhaust fans, and caulk those openings. Beetles already in the walls will use them.
• Skip bug bombs and sprays. Penn State says foggers kill beetles on ceilings but don’t stop more from emerging, and that dead beetles in wall voids can draw carpet beetles, which can damage woolens and stored goods. Ohio State also warns against bug zappers: a zapped beetle can burst and spray a staining, foul-smelling fluid.

When to call a pro

Call a pro if beetles keep appearing after you’ve sealed gaps, or if you find large numbers in an attic or wall voids; Penn State says it’s not uncommon for tens of thousands to gather in attics, ceilings and wall voids. Penn State says it isn’t advisable to use an insecticide once beetles are in wall voids or attics. Penn State and Minnesota both say an exterior insecticide treatment goes on in late September or early October, before the beetles gather, and Ohio State says these products are for licensed applicators, so by late October that window has mostly passed and the useful questions for a pro are sealing and next September’s prevention. If anyone in the home has allergy-type symptoms around the beetles, mention it to a doctor.

Asian Lady Beetles: common questions

Where in Delaware

Where Asian lady beetles rank on each county’s top-pest list:

• New Castle County Not in the county top six
• Kent County Not in the county top six
• Sussex County Not in the county top six

Sources

• University of Delaware Cooperative Extension, Kent County — Fall House Invaders 2: The Multicolored Asian Lady Beetle (2009)
• University of Delaware Cooperative Extension, Kent County — Controlling Fall Invading Insect Pests (2009)
• Penn State Extension — Multicolored Asian Lady Beetle
• Ohio State University Extension — Multicolored Asian Lady Beetle (ENT-44)
• University of Minnesota Extension — Multicolored Asian lady beetles