We Are Being Invaded!

It began yesterday. I first noticed them when I was outside doing some of the annual chores to prepare my yard and home for winter – splitting and stacking firewood, cleaning window screens and raking leaves. All of a sudden, around noon, as the temperature warmed to about 60 degrees, great swarms of silent little creatures filled the air. I could see hundreds of them without even turning my head, and when I did turn it to look in a different direction, I saw MANY, MANY more of them.

After doing a bit of research, I learned that this seeming invasion of tan and orange Asian lady beetles (Harmonia axyridis) isn’t really an invasion. It is simply a massive relocation effort – each fall, adult beetles leave their summer feeding sites in yards, fields and forests in search of protected places to spend the winter. Swarms are heaviest on sunny days following a period of cooler weather (such as we experienced over the weekend) and most flight activity occurs in the afternoon. The intensity of swarms varies from one day to the next depending upon the weather.

As their name suggests, Asian lady beetles are not native to the United States. They were brought into this country in the 1960s by the U.S. Department of Agriculture to control agricultural pests on crops such as pecans and apples, and they have since established thriving populations that reach into Canada. In their native lands, Asian lady beetles live mainly in trees in forests and orchards. Here though, they take up residence in ornamental and agricultural crops as well as suburban areas. In the spring and summer, the larvae and adults feed mainly on aphids, consuming hundreds each day.

As they seek out winter homes, Asian lady beetles head for bright areas. They congregate on the southwestern exposures of buildings, and they are especially drawn to dwellings that have light and dark contrasting features i.e. dark shutters on a light background. The 200 year-old house at Fairview Farm that now serves as the office of the Upper Raritan Watershed Association is a textbook example of this phenomenon – the house is painted white, its shutters are dark green, and it is absolutely covered with beetles on its southern facing side! Once they land on buildings, the beetles begin a search for crevasses and cracks in which to crawl. They make their way into attics and wall cavities, where they remain until temperatures warm up again in the spring and they re-emerge to return to fields, forests and lawns. Unfortunately, their journeys can take them throughout the entire house – our office is literally crawling with them today.

Although they are a nuisance, Asian lady beetles generally don’t cause much damage or harm people. They do, however, emit an acrid odor and can stain surfaces with their yellowish secretions when they are disturbed (this is a defense mechanism they employ to deter predators), and they sometimes bite (speaking from experience, I can assure you that their bite isn’t ferocious – it feels like a small pinprick, at most, but it is rather startling).

If Asian lady beetles have found their way into your home and you don’t want to host them all winter long, your best move is to get out a vacuum cleaner. If you attempt to use a broom to sweep them back outside, you may have a significant clean-up in store to remove the yellow stains on your walls and floors. We do not recommend that you use an insecticide to eliminate Asian lady beetles from your home – too many other creatures may be killed. Instead, next spring or summer, seal up the cracks around windows, doors, soffits, fascia and other openings into your home. By doing this, you’ll create a barrier that will prevent Asian lady beetles and other pests from getting into your home. For now, get out the vacuum cleaner, and know that the cooler weather ahead will stop the swarming soon!

Susan Brookman, Membership Program Director
Photo courtesy of Iowa State University