By Reeve Gutsell For the Gazette
In recent years, many New Englanders have noticed an abundance of ladybugs congregating near the walls and windows of their homes during the end of autumn and re-emerging during spring.
These non-native harlequin ladybugs (Harmonia axyridis: actually a beetle, not a “bug”) are an invasive species that were introduced to North America in 1916 to control scale insects and aphids, both of which are major crop pests. Although they did successfully control aphids, harlequin ladybug populations didn’t establish in the wild until 1988, when one wild population was noticed near New Orleans. Since then, they have spread throughout much of North America, as well as into Europe, South Africa and South America.
In the United States, these ladybugs often appear indoors in the fall after leaving their summer feeding sites: fields, farms, forests and yards. They are particularly attracted to southern-facing, light-colored buildings and/or high-contrast buildings near fields or woods — a common condition of many New England homes. (This preference is thought to reflect their native habitats in Asia, which are limestone cliffs.)
They may swarm anywhere from September to November, depending on location and weather conditions.
Once they have found an attractive location, they seek out protected areas to spend the winter, such as crevices, wall cavities and attics. They are often drawn to sunny windows and door frames, areas behind siding and within soffits, and structures in poor repair with many cracks and openings.
Anyone who has never experienced this phenomenon, or has not experienced it to a large degree, may wonder “So what? Ladybugs are great — they eat aphids! That’s helpful, right?” This is true — in fact, harlequins are a major predator of soybean aphids, another invasive species from China.
The problem with these ladybugs is twofold. One is their invasive nature. As previously mentioned, once established in the wild, they spread rapidly throughout North America and Europe. A 2011 study done in Britain and Ireland found a 20 percent decline in native ladybug species since the harlequins’ arrival in 2004, due to a combination of changed climate and strong competition from these insects.
An additional reason for the harlequin’s success is not only that it is highly resistant to diseases that affect other ladybird species, but also that it carries a microsporidian parasite to which it is immune but that can infect and kill other species. Harlequin ladybugs also eat some competing species.
The second problem is the general nuisance they can cause to the homeowner. In a defense known as “reflex bleeding,” harlequin ladybugs (both larvae and adults) release an alkaloid toxin through their leg joints whenever they are frightened (or squashed). Designed to deter predation, this toxin releases an unpleasant odor and causes a yellowish stain. (Incidentally, this is an increasing problem in vineyards, when ladybugs get mixed with harvested grapes and cause an unsavory flavor in wine known as “ladybug taint.”)
Harlequin ladybugs also can bite, although this is not generally a significant problem except in cases of allergy.
Harlequin ladybugs are known by many other names, including Asian, Halloween, (because they enter homes in late October), multivariate, southern, Japanese, pumpkin and, in the UK, “many-named ladybirds.”
As the variety of common names may indicate, harlequin ladybirds are highly variable in their coloration, which can make identification a challenge. They are generally rather large (for a ladybug), always have reddish-brown legs, and are brown on the underside of the abdomen.
Many, though not all, harlequin ladybugs have an “M” or “W” on the pronotum — the section between the elytra (hard wing coverings) and the head.
During warm weather, predatory ladybugs such as harlequins are usually found on or near plants that harbor their prey — in this case scale and aphids. They lay clumps of a few to several dozen oblong, yellowish eggs near the prey, to increase the likelihood of the larvae’s survival. Eggs hatch in 3-4 days, after which the larvae pass through four instars over 10 to 14 days. Then they enter pupation, followed by several days of a soft, post-molt phase, after which the adults become reproductively active prior to overwintering. The average life span is one to two years.
So what is a homeowner and/or ecologist to do?
Gardeners who wish to combat harlequins can learn to identify the various life stages (being careful to distinguish them from native species) and remove them from plants by hand, putting them in soapy water.
To defend against home invasions, seal cracks or other spaces that are 1/8 inch or larger, including window screens, vents, and door seals. It is best to do this by the end of September, before the overwintering process starts. (Note that native species do not generally invade homes.) If the ladybugs are already inside, remove them by vacuuming. Before starting, attach a nylon stocking to the vacuum’s extension hose with a rubber band, and use this to suck them up. Once vacuuming is complete, remove the stocking and tie it closed to prevent the insects’ escape. To dispose of the ladybugs, freeze the stocking for at least three hours or submerge it in soapy water.
Reeve Gutsell is a volunteer at the Hitchcock Center for the Environment. She has a master’s degree in resource management and conservation from Antioch University, and an MFA in Creative Writing from Naropa University. She enjoys spending as much time as possible exploring the Pioneer Valley.Click here to return to full list of Earth Matters articles.