The Ladybugs are Coming ...

Whether in folklore or science, ladybugs are nearly always revered as beneficial or helpful insects. Their activities have been instrumental in controlling insect pests of important food crops here in the United States. In fact, the first use of a beneficial insect to control an insect pest in the United States was the ladybug Rhodolia cardinalis to control cottony cushion scale in California. This success led to the release of other ladybug species to control a variety of insect pests. It is estimated that over one billion ladybugs are now sold every year to gardeners across the United States.

Despite all of the good they do, some ladybugs are a nuisance at certain times of the year. In the fall, when outside temperatures decrease, ladybugs assemble in protected locations to hibernate. Houses and other buildings attract the beetles as good hibernation areas, and they congregate on the outside walls, porches, decks and around windows and doors. They come indoors through cracks and crevices and poorly fitting window screens. Once inside, they fly about and crawl along walls, furniture and ceilings. At first, it may not seem to be a big problem, and the homeowner may even think they are cute, but eventually their numbers increase and their activities become a nuisance. Additionally, when squashed or touched, they release an odorous chemical that can stain walls and fabrics. These same problems also occur during spring, when ladybugs break hibernation and try to disperse out of their hibernation areas.

Most of the ladybug invaders belong to the species Harmonia axyridis (the multicolored Asian ladybug). Harmonia was introduced throughout the U.S. and Canada in the late 1970s. It is a very beneficial insect, feeding on aphids, mealybugs, scales and other soft-bodied insect pests during the summer, but it has also become a serious pest during aggregation and hibernation periods. During fall, these beetles seek out large objects in the landscape in which to aggregate and seek shelter. In their native lands, they typically overwinter in cliffs. Harmonia are about 1/4 of an inch long, and their color is variable. Color patterns range from beige to yellow to yellowish orange to bright reddish orange, with anywhere from 0-19 black spots. Regardless of the color or number of spots, one distinguishing feature of the Asian lady beetle is the coloration of the area behind the head. This area is called the pronotum and is consistently white with a black M-shaped mark.

The most effective method of reducing the nuisance activities of Asian lady beetles without reducing their beneficial activities is to prevent them from entering homes or buildings. This can be difficult but is best accomplished by sealing cracks and crevices they might use to gain access to a structure. Use good quality caulking around doors, windows, siding, foundation and utility entry points. Screening can be installed over attic, crawlspace and utility exhaust vents. Window screens that do not fit the window frame snugly, or have holes in the screening, should be replaced. If desired, an insecticide application can be made to the susceptible areas on the outside of the structure by a licensed, commercial pest management company. The timing of this application should occur somewhere around the first week of October. These preventative activities are also helpful in reducing the risk of infestation from spiders, such as brown recluses, and other nuisance insects such as crickets, ants, beetles and wood roaches.

Ladybugs that get inside the home can be collected easily using a vacuum cleaner. Vacuuming does not kill the ladybugs and also reduces the danger of wall and fabric stains that result from handling or crushing them. If you vacuum up large numbers of ladybugs, you can empty the bag outside to help preserve their beneficial activities. However, remember that the bag should always be emptied soon after vacuuming to reduce the number of dead ladybugs in the bag and the threat of odor from the chemicals released by them. This odor can become permanent and noticeable each time the vacuum cleaner is used if the bag is not emptied reasonably soon.

Although beneficial during much of the year, the multicolored Asian lady beetle can be a serious nuisance pest at certain times. Although not known to be a threat to human health, clothing, food or pets, their habit of congregating in and around our homes makes them undesirable as well as beneficial. Efforts are underway to examine the full impact of these beetles and to develop better methods of managing their populations during periods of aggregation.

Richard Houseman, Urban Entomology Specialist, UMC, (573) 882-7181