If you live near a wooded area and have any type of minute crack in the exterior of your home, then you have undoubtedly been visited by a creepy, crawly winter guest over the years. The Asian lady beetle (Harmonia axyridi) seeks refuge in rocky bluffs to spend the winter in its native range, but often mistakes our home for winter refuge given the lack of rock outcrops in central Illinois. They have the uncanny ability to squeeze and crawl their way to the smallest cracks in exterior siding, windows and doors, often making it to interior rooms in our homes.
Since our homes are warm, they remain active upon reaching the interior, landing in open drink containers, buzzing around lights and winding up in your hair or on the back of your neck. Although they don’t often bite, when they do it can be quite the pinch. Their worst feature, besides being overly persistent, is likely the smelly yellowish fluid they exude from their leg joints as a defense mechanism.
Although these winter visitors can certainly raise our ire, I have to give them some credit on the positive side. The Asian lady beetle is a voracious predictor of many insects, such as aphids and scale, that are pests of agricultural crops and gardens. In their native range, they feed primarily on aphids in trees, a habit that makes them more prevalent near wooded areas in Illinois. Consequently, these beetles are noted to have the greatest positive impact on crops of woody plants, such as orchards. They have also been credited in reducing numbers of certain pests on major agricultural crops, such as the soybean aphid, thus reducing the need for pesticide controls to protect yields.
Although Asian lady beetles are an interesting use of biological control to reduce pest populations and subsequent pesticide use, lessons learned from past introductions of exotic species have taught us about the unintended negative impacts to ecosystems. While the beetles have generally been considered a positive, they have put pressure on our native lady beetle (or ladybug) populations, which are not as aggressive and have trouble competing for food.
Interestingly, there is still some mystery surrounding the introduction of the Asian lady beetle in the US. Attempts to introduce the species were mounted as early as 1916 in California and continued through the early 80’sin multiple eastern and southern states. However, no successful overwintering beetles were ever detected following an introduction event. In the late 80’s, an established population was discovered in Louisiana, near New Orleans, which cannot be directly linked to a known introduction. To this day, it is unclear if accidental introduction or intentional release programs established the species.
Although Asian lady beetles are generally viewed as positive in the horticulture world, they can be a downright aggravating as winter roommates. Prevention is the most effective step in controlling indoor populations during the winter months.
Homeowners should begin by sealing all exterior cracks around windows, doors and foundations. Often times significant cracks are present where siding meets at corners or along roof soffits. I have had pretty good success reducing lady beetle numbers by sealing the exterior of my home. As a secondary mode of defense, look to seal interior cracks and pathways such as holes for pipes or electrical fixtures. Although lady beetles may overwinter in your walls, it may be of little consequence if they cannot enter interior rooms.
If you are unsuccessful at stopping the onslaught of these little critters, there are some effective indoor traps on the market. Research has shown that Asian lady beetles are attracted to light. They tend to congregate more on lighter colored buildings and anyone who has a significant indoor population in the winter has observed their habits on light fixtures. Indoor traps are constructed using a light bulb and some kind of trapping mechanism. They typically use a black light and are turned on overnight to trap the beetles while you sleep. Multiple companies sell the traps online and I have even found some pretty good plans for DIY traps, although they don’t look quite as nice as those for sale.
If you suffer from a heavy winter beetle infestation, I wish you the best in all control efforts. They can be quite difficult to curtail. The thing to keep in mind is that although they are bothersome and downright smelly during the winter months, they may be eating enough pests during the (much longer) growing season that we actually experience a positive overall impact from these little guys.