During the fall when the weather is cooler, the mul-ticolored Asian lady beetle, Harmonia axyridis, congregates on the south side of buildings and enters homes. The beetle does this because in their homeland of China they inhabit tall cliffs to overwinter. As you know, there are very few tall cliffs in Illinois, so the next best thing is a building.

The multicolored Asian lady beetle is a native of Asia and was introduced into the southeastern and southwestern portions of the United States to deal with aphids on pecan trees. It spread rapidly to other portions of the country. It is a tree-dwelling lady beetle, more so than the native species, and a very efficient predator of aphids and scales. Adults also feed on ripening peaches, apples, and other fruit, eating shallow holes in them. This damage is easily controlled with commonly used fruit insecticides.

The multicolored Asian lady beetle can be easily distinguished from other species of lady beetles by the presence of a pair of white, oval markings directly behind the head, which forms a black M-shaped pattern. Adults are 1/4 inch long, 3/16 inch wide, and yellow to orange colored. In addition, their bodies are usually covered with 19 black spots. Adults can live up to 3 years. Female beetles lay yellow, oval-shaped eggs in clusters on the underside of leaves.

The eggs hatch into larvae that are red-orange and black in color, and shaped like an alligator. The larvae are primarily found feeding on soft bodied, plant feeding insects such as aphids and scales. They eventually enter a pupal stage. The pupae can be seen attached to plant leaves. Adults emerge from the pupae and start feeding on aphids. These adults can be found on a wide variety of trees including apple, maple, oak, pine, and poplar. There are multiple generations per year.

The multicolored Asian lady beetle is a nuisance pest because the adults tend to congregate and overwinter inside buildings in large numbers. They release a pheromone that attracts more beetles to the same area. Although they may bite, they do not injure humans nor can they breed or reproduce indoors. They are attracted to lights and light-colored buildings, especially the south side where it is warm. The beetles then work their way into buildings through cracks and crevices. Dark-colored buildings generally have fewer problems with beetles.

Beetles can be prevented from entering homes by caulking or sealing cracks and crevices. Beetles already in homes can be removed by sweeping or vacuuming. Be sure to empty the vacuum bags afterward. Do not kill the beetles. Just release them outdoors beneath a shrub or tree away from the house. Commercially available indoor light traps can be effective. If crushed, the beetles will emit a foul odor and leave a stain. The dust produced from an accumulation of dead multicolored Asian lady beetles behind wall voids may trigger allergies or asthma in people. Insecticides are not recommended for use indoors.

Homeowners who want to avoid dealing with overwintering beetles entering their homes can hire a professional pest-control company to treat the points of entry on the building exterior with a pyrethroid insecticide. The treatments need to be made in late September or early October before the beetles enter the building to overwinter.

The beetle has been able to spread rapidly throughout portions of the United States because it was introduced into the country without its native natural enemies. However, populations may decline as cosmopolitan natural enemies start attacking them. For example, studies in North Carolina have demonstrated that up to 25% of the beetle populations are being parasitized by a tachinid fly.