Asian lady beetle
Asian lady beetle (Photo credit: John Obermeyer, Purdue Entomology)

Here is a riddle. What is orange, shaped like a pumpkin, and found just outside your door on Halloween night?

If you answered "jack-o'-lantern," then your home is obviously not being invaded by lady beetles - like many throughout the country. The fact that these nuisance lady beetles are orange, have the same general convex shape as pumpkins and are active in late October also gives rise to their common name of "Halloween beetle." Their scientifically accepted common name is multi-colored Asian lady beetle, but we most often call them Asian lady beetles for short.

By the end of October, frustrated homeowners often call them much worse names - many of which cannot be printed here. Regardless of what people call them, they are never as welcome at your door as the cute, costumed trick-or-treaters from down the street.

Asian lady beetles congregate on buildings in large, unwelcome numbers, and then they squeeze under siding, sneak into cracks and crawl through small openings near windows and doors on the outside of your home. But these trick-or-treaters won't go away even if you offer them candy. They take the "trick" of trick or treat to the extreme, for once they get a foot in your door, they insist on taking up residence there the whole winter. What's worse, if you try to evict them or shoo them away, they emit a very nasty smell that can leave your eyes watering. They do this via a process called reflex bleeding. If agitated, they emit a nasty, yellowish secretion from their leg joints and if a whole lot of them are disturbed, they can produce a very potent, repugnant smell that really stinks up the place. Not only that, but recent studies suggest that heavy infestations can exacerbate allergies in some individuals, ranging from eye irritation to asthma.

Not all lady beetles are prone to such bad behavior. Several native species are similar in size and color to multi-colored Asian lady beetles. They are very beneficial in our gardens, because they prey on potentially harmful insects such as aphids. The difference between these native lady beetles and the Asian lady beetle is respect. Native lady beetles respect a person's home. They do not invade. In fact, they are not even attracted to homes. The Asian lady beetle, on the other hand, has the obnoxious behavior of wanting to pass the winter inside your home. In the process, they give all other lady beetles a bad name.

Asian lady beetles are relatively new to this country. They originated in Asia (as their common name suggests) and have only been in the United States since about 1988. Believe it or not, from the 1960s through the 1990s, the Department of Agriculture intentionally introduced Asian lady beetles to help control agricultural pests, especially of pecans and apples. They released large numbers of them in several states including Georgia, South Carolina, Louisiana, Mississippi, California, Washington, Pennsylvania, Connecticut and Maryland. We don't know whether those releases are responsible for the beetles we have now or whether a 1988 accidental infestation in Louisiana (via a Japanese cargo ship that was reported to be infested) is to blame. But we do know that frustrated homeowners are looking to blame someone. When these beetles appear by the thousands inside a home, someone is going to get blamed - and it is usually an entomologist.

An irate caller once accused me of being the one (yes, me personally) who introduced them to Indiana via a poorly planned research project at Purdue University. I will admit to a poorly planned research project or two in my Purdue career, but rest assured that I have never introduced lady beetles of any kind. I pointed this out to the caller, and then said that Bloomington (home of Indiana University - Purdue's in-state rival) reported seeing Asian lady beetles long before anyone at Purdue ever complained. Confession: I'm not sure that is exactly true and doubt that IU was ever involved, but hey, it got the caller off the phone and I felt a whole bunch better.

What we do know for sure is that those beetles invading our homes right now are the same species (Harmonia axyridis) that live in trees and fields in Japan, Korea, China and Russia.

After the first noticeable populations in the United States were found in Louisiana in 1988, they slowly expanded their range, which now includes much of the United States and even parts of Canada. Farmers and orchardists love this beetle because it eats aphids and scale insects in trees and fields. Asian lady beetles have probably saved farmers millions of dollars by taking out these pests.

Homeowners, however, view them differently. Swarms of Asian lady beetles fly to buildings from September through November looking for a place to shelter for the winter. They are most likely to appear on the first warm sunny days after a period of cooler weather. Consequently, the most intensive flight activity frequently covers the afternoon of October 31 - Halloween.

Most complaints seem to come from homeowners who live near rural areas. Our anecdotal research has confirmed that tall, light-colored buildings close to woods and fields are prime targets. Even more particularly, these beetles congregate on the southwest sides of the buildings and mostly near dark areas that contrast with the light-colored siding, such as under eaves and next to windows and doors. Apparently, these remind the beetles of cavities in limestone cliffs and outcroppings where they pass the winter in their old country. Here in America, they seem happy to adapt.

Asian lady beetles are proficient at seeking out and entering cracks and small openings, and then squeezing their way into the building proper. As the temperatures continue to drop, they end up in large masses in soffits, attics, wall voids and other protected locations.

Once comfortably inside the building, freeloading Asian lady beetles fall into an inactive period when they do not eat, drink or move much. They just laze about in huge sedentary huddles of disgusting beetles all winter long. That is, until temperatures improve in late winter and early spring. With the warmup, the beetles awaken, become active and apparently begin thinking about getting back to the outdoors. However, their winter nap seems to play havoc with their tiny memories such that they completely forget how to get back outside, so they end up emerging from behind baseboards, wall voids, attics and suspended ceilings, right into the interior of our homes to become a bother for a second time. Even if you know that Asian lady beetles won't harm you directly by biting or infesting food, they can drive you mad when they emerge by the hundreds or thousands and randomly appear on walls, climb on cabinets, or fall into cereal bowls or dinner plates - just about anywhere you can imagine.

So, what can you do?

Chemical warfare is not very effective after the beetles are securely indoors. It is difficult to get pesticides to penetrate areas where they hide and, because the beetles do not awaken all at once, using aerosol sprays on a daily basis over the span of several weeks is not recommended. The internet advertises a multitude of traps, baits, lights and other solutions, but customer reviews are not encouraging. Most residents fall back on the tried and true broom and dustpan technique, even though this method is likely to cause the beetles to emit their smelly, offensive secretion. Some advocate that a better way to remove them is with a vacuum cleaner. This may also cause them to smell but at least the stench can be contained in the vacuum and can be mitigated by changing out the bag.

An even better method of dealing with lady beetles is defense. Prevent them from entering the building in the first place by sealing up cracks or holes that allow access. Make certain that doors and windows are in proper condition. Tight-fitting door sweeps or weather stripping should prevent them from entering under doors or around windows. Inspect window screens for tears or rips, and install screens behind exhaust and attic vents. Use all-purpose sealant in smaller cracks and openings around windows, doors, soffits, fascia boards, chimneys and utility ports, and plug larger holes with urethane foam or copper mesh.

Applying pesticides as outside perimeter treatments during late fall will also help prevent beetles from getting into a home. Remember that sunlight breaks down insecticides, which greatly reduces their residual on the building exterior, rendering them ineffictive much beyond several days or a few weeks, depending on the chemical.

The key to preventing Asian lady beetles from becoming a home nuisance is to have these defenses in place before the beetles begin looking for shelter in the fall. If you can keep the beetles from entering your home, you will have won the battle.

Like other introduced pests, Asian lady beetle populations initially exploded out of control, but have since gradually subsided. Although we will never be entirely rid of Asian lady beetles, we can expect to see their high numbers continue to level off and to decline over time. If this fact does not give you comfort and if you still want someone to blame, call me. I'll pass along IU's direct telephone number.

Dr. Tim