Asian lady beetles swarm to shelter in autumn

lady beetle photo by USDA ARS
Last Updated: 
October 8, 2010

CORVALLIS, Ore. – In some years, large numbers of ladybugs may converge on your house during autumn – at your windows, outside walls or on the garage. Ladybug, ladybird and lady beetle are a few of the common names for this well-known beneficial predatory insect.

There are more than 450 species of these colorful beetles in North America alone. The most common native species of lady beetle found in Oregon is the convergent lady beetle, Hippodamia convergens, according to Amy Dreves, entomologist in the Department of Crop and Soil Science at Oregon State University.

Other species found in Oregon include the imported Asian lady beetles, of the species Harmonia axyridis.

People often think of lady beetles as only being red with black spots. But these adult Asian lady beetles are quite variable in color from individual to individual, ranging from red, orange or yellow to black with as many as 19 black spots or none at all, explained Dreves. Some are all black with a red spot on each side of their wing covers. Be careful not to mistake the 12-spotted cucumber beetle or Mexican bean beetle for a beneficial lady beetle, she warned.

All types of lady beetle adults eat harmful insects, including many types of aphids, explained Dreves. As aphids feed on plant sap, they excrete a sugary sticky substance called honeydew. Honeydew is eaten by ants as well as by lady beetles. In its lifetime, a lady beetle can eat more than 5,000 of these little plant-sucking pests.

If lady beetles are swarming to your shed or house in the autumn, they are most likely these multi-colored Asian types, said Dreves. Unlike Oregon's native lady beetles, which migrate to the mountains of Oregon and California to over-winter, the Asian lady beetles remain in western Oregon to find a winter home. They appear to prefer light-color or sunny sides of buildings, windows and fixtures this time of year.

"They like to hang out together in groups, preparing to hibernate and spend the winter kind of shut down," she said. "They don't feed. Instead, they live on their fat reserves that they store up during their feeding stage. In the spring they will wake up and disperse, mate, lay eggs and then die."

These large swarms don't occur every autumn, said Dreves. Some years large numbers are found, in others, few may be seen.

Asian lady beetles typically produce about three generations per year, taking about six weeks to grow from the egg stage through the larval stage to the adult stage.

In the spring, they wake up, fly about and reproduce. After laying eggs, the next generation of larvae, or immature life stage of the Asian lady beetle, begins feeding on soft-bodied pests found in gardens and greenhouses, such as aphids, whiteflies and mites.

Found throughout the spring and summer, ladybug larvae resemble miniature carrot-shaped alligators with minute flexible spines, said Dreves. They are one-eighth to one-half inch long, somewhat flat, warty in appearance and are usually black or gray with a little orange color on four or five segments of the abdomen. They do not have wings or wing covers.

The Asian lady beetles do not sting or carry diseases. But in large numbers, they are somewhat of a nuisance to many people. They can produce an odor and leave a discolored "spit." Also, they can exude a yellow-orange-colored substance from around their joints. And they can pinch your skin with their mandibles.

Dreves recommends an array of choices for coping with ladybug invasions:

Repair damaged screens, gaps, leaky door cracks, broken seals on windows and other openings that may allow lady beetles in. Seal up openings with silicone caulking, weather stripping and/or foam. Install insect screening over your attic and exhaust fans. Install door sweeps.

Collect lady beetles off walls and building sides by sweeping them with a soft brush into a container that you can put air holes into, such as a paper sack, jar or coffee can. But be forewarned that if you disturb them they may bleed a yellow-orange slimy fluid through their joints that may smell, stain walls, paint and fabrics. Place straw or some other kind of dry substrate into the container with a lid. Keep them in the fridge all winter, and then let them go in the spring after it starts warming up.

"There is no guarantee that they will survive or stay around, but they may fly away and feed on pest insects somewhere," she said. "If you grow nectar-producing plants that beneficial insects prefer, such as yarrow, alyssum, sweet fennel, hairy vetch, flowering buckwheat and caraway, the ladybugs may be encouraged to stick around."

If they become intolerable nuisances, vacuum them up. But remember, this may kill them.

Trap them with a light trap with baffling so the beetles go in toward a light source, then can't find their way out. Collect them in a cloth sack, then store them in a cool area and release the beetles in the spring.

There are no registered pesticides for use on these beetles, so do not use pesticides to try to control lady beetles.

The OSU Extension 4-H program has produced a publication about lady beetles (EC 1604). You may download it at: http://ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/19819/ec1604.pdf. To purchase a printed copy, call 1-800-561-6719.

Author: Carol Savonen
Source: Amy Dreves