As the weather turns cool, insects begin to look around for a nice place to settle in for the winter. Unfortunately, a few species may choose your house. The multicolored Asian lady beetle is one such invader that starts looking for lodgings in late summer and early fall.
Harmonia axyridis is a yellow- to orange-colored lady beetle that often is seen in large congregations on buildings around the end of October – hence one of its common names, the Halloween lady beetle. The “multicolored Asian lady beetle” is the preferred common name for this lady beetle introduced from Japan for control of tree-inhabiting aphids. The USDA made several attempts, starting in 1916, to introduce this beetle into the US, but it never got established until releases made in Louisiana and Mississippi in 1979 and 1980. From there it spread to other southern states and now is widespread throughout North America. This species was first recorded in Wisconsin in 1992, but quickly spread around the state.
The adult lady beetle is quite variable in appearance. Individuals can be any color from a pale yellow-orange to a deep orange-red, and have from no to more than 20 black spots. They are very prolific and may live up to three years. The bright yellow eggs are laid in clusters of about 20 on the undersides of leaves. The eggs hatch in three to five days, and the larvae feed up in the trees for 12 to 14 days. They then pupate on the leaves and adults emerge in five to six days.
In its native area the multicolored Asian lady beetle is mainly an arboreal species feeding on various aphids, certain scales, and a few other insects. In the US it inhabits various trees, including maple, walnut, willow, and oak, as well as other plants. It is an effective predator of aphids on pecans, pine trees, ornamental shrubs, roses, and other plants. In many areas pecan growers no longer need to spray their trees for pecan aphid because this lady beetle has done such a good job of biological control. It was also found to feed on soybean aphid, accidentally introduced from China, which likely aided its increase in the Midwest when that aphid became a significant problem in vast acreages of soybean in 2000. Beetle populations tend to explode when there is an abundance of aphids, often eliminating the local aphid population.
Even though this lady beetle is an important biological control agent, it can become a nuisance when they aggregate in large numbers on homes or other buildings. For several days during autumn they typically cluster on sunny, southwest sides of light-colored rock outcroppings or structures (especially clapboard siding). In their native habitat these colonies would find refuge in crevices of cliffs and rocky hillsides to hibernate. Here, they will also move into leaf litter, underneath boards or logs, or other protected areas after the first frost.
Homeowners, however, complain when there are thousands of beetles covering their house, they have to walk across piles of them on the deck, they get in picnic food and drinks, “swarm” like bees and land on people, and especially when the beetles get in the house. Outdoor aggregations may leave voluntarily after a few days or weeks, but, as experienced crevice finders, they often find their way through tiny cracks into the walls, around uncaulked window frames, into attic areas, and other areas. When warm days bring them out exploring, if they go the wrong direction, they end up in the house.
The best way to prevent beetles from becoming uninvited houseguests is to seal cracks around windows, doors, siding, utility pipes or other openings with a good quality caulk. Replace or repair damaged screens, and install screens over roof vents. Sprays are a temporary secondary solution. It’s important to act quickly when an invasion begins because the bugs can be almost impossible to kill or remove once they’ve found a snug spot to spend the winter.
The best way to deal with lady beetles in the house is to vacuum them up (but don’t use an attachment with a beater bar, since it will crush the beetles and may stain carpets). They can also be swept up with a broom and dustpan and be deposited outside well away from the house. Killing them with insecticides, squashing them, or handling them may result in orange stains on walls and fabric. When stressed the lady beetles secrete a harmless, but staining, orange substance. This liquid is actually blood that comes our of the joints of the legs – a phenomenon called reflex bleeding (all lady beetles do this when stressed).
– Susan Mahr, University of Wisconsin – Madison
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- Multicolored Asian Lady Beetle — UW-Extension Wisconsin Garden Fact Sheet XHT1050
- Ladybug – Multicolored Asian Lady Beetle – Iowa State University Insect Notes
- The Multicolored Asian Lady Beetle – a USDA fact sheet
- Harmonia axyridis – on Cornell University’s Biological Control: A Guide to Natural Enemies