How to keep vicious ladybugs out of your house

(Shikha Subramaniam/The Washington Post)
(Shikha Subramaniam/The Washington Post)

Few people want to share space with insects. Long legs, quivering mandibles and segmented bodies skittering across walls or floors make many of us uncomfortable; for some, they're downright terrifying.

Then, there are ladybugs: no less an insect, but somehow dearly beloved -- and even celebrated -- by many. The little red beetles appear as a motif on clothes and decor. We sing songs about them going on a picnic, and we consider them a sign of good fortune. Considered more cute than creepy, they evoke far more whimsy than fear. So when people begin to see a lot of ladybugs around, including inside their houses at this time of year, it might not seem like a problem.

Not so fast. Ladybugs are in fact voracious predators, and the type that get inside human spaces in the fall are an invasive species that could be doing more harm than good, both to our homes and to the greater ecosystem.

How ladybugs were lucky

Ladybugs, also called lady birds and lady beetles, are biological control agents that eat pests and protect crops, says John Losey, a professor of entomology at Cornell University.

"People have known they're important for thousands of years. Farmers realized if they had a crop beset with pests, ladybugs could save it," he says. "They'd pray to the Virgin Mary to send them, and that's how they got their name. And when they did come, the farmer would have good luck against the pests; they're still considered good luck today."

That helpful nature, coupled with their appearance, is what makes them so appealing, Losey adds, even to the bug-averse. "Ladybugs are these brightly colored little blobby hemispheres, with the legs sort of tucked under. They look friendly," he says.

Unless, of course, you're an aphid: "It's just because you can't see their mandibles, their teeth," Losey adds. "If you did a real close-up and saw them eating an aphid, and legs are dropping off and parts of the aphid are still squirming ... it's brutal."

It was one ladybug variety's particularly ravenous appetite that brought it to the United States. The multicolored Asian lady beetle, Harmonia axyridis, was introduced sometime in the 1980s to control aphids, whiteflies and other pests. "The idea is that a lot of our crops are foreign -- like soybeans, which come from Asia -- and that brings in foreign bugs," Losey says. The Harmonia ladybug, an especially efficient hunter, was imported for increased pest control. Unfortunately, the variety spread much faster than anyone could have predicted.

"It's unprecedented," he says. "Now, not only is it the most common species in North America, it's the most common ladybug species anywhere in the world."

Crawling into the cracks

In their native range -- across China, Japan, Korea, Mongolia and parts of Russia -- Harmonia ladybugs overwinter in piles of rock and in the cracks and crevices of cliff faces. So when late fall arrives in the United States, Losey says, "they're flying around looking for cracks. They come to your house and think, 'Well that looks like a cliff face,' and they see the line of your door or window and think, 'There's my crack.'"

The bugs can enter these tiny gaps in massive numbers, and they stay put until spring. Most of the time, anyway. "If you have a warm day in the winter, they think it's spring and you'll see them activate," says Ben Hottel, a technical services manager with pest control company Orkin. "You'll get beetles rushing into your home and running all around your house."

There can be drawbacks to the beetles' presence, Hottel says. While they're not aggressive or venomous, they can bite. If they die while holed up in your walls, the dead bodies can trigger allergies. "And they do have a response, if you disturb them, where they might actually do what's called reflex bleeding," Hottel says. "They excrete some of their blood as a defense mechanism. It can be a little smelly."

In other words, having large numbers of ladybugs overwintering in your home can be rather unlucky. But homeowners can take some pretty basic steps to make their houses less appealing.

"Simply sealing things up is one of the best things you can do for preventing any insects from getting inside, but especially lady beetles," Hottel says. Check for gaps around doors and windows, and seal them with caulk. "Weather stripping on doors gets worn away over time, and if you can see any spots of light under the door, that's big enough for insects to get through. Look around outside everywhere you have gas or utility lines, or anything going into the wall of the structure, and check the seals there, too."

It's also helpful to install a heavy-duty seal on garage doors, Hottel says, and "if you have gable vents or roof soffits, you can get insects and things trying to get in there. Making sure those spaces are filled or you have tight screens can prevent it."

The lost ladybugs

While Harmonia axyridis is the most common variety, it's far from the only ladybug. In fact, Losey says, "there's approximately 500 species in North America and 5,000 worldwide." Most species are under a centimeter long, and they all have the trademark protective shell over their back. But some are more oval-shaped, while others are round, and they can range in color from black and brown to various shades of red, orange and yellow. Some species have many spots, and others have none.

Unfortunately, many of those native ladybug species are in decline, and Harmonia axyridis may be at least partly to blame. The Asian ladybugs outcompete the natives for food and habitat, and their larvae grow faster than other ladybugs', so they will sometimes eat the smaller, immature natives.

"What we've seen is a change from a really diverse set of native species, to a much less diverse set of species that are dominated by the Asian ladybug," Losey says. "Every ladybug does its job a little bit differently, so the best pest management comes from a really diverse set of ladybugs."

Losey heads up the Lost Ladybug Project, which uses volunteer-submitted photos to collect data on their numbers and get a sense of just how steeply some species have declined.

"One of the main ones I've worked on is the nine-spotted ladybug. It was so common in New York that it was named our state insect," Losey says. "It has now declined by I'd say 80% to 90% of its population."

Invasive ladybugs are almost certainly here to stay, he adds, but achieving a better balance between the newcomers and native ladybugs is possible.

Making your home an undesirable hibernation spot for Harmonia axyridis could mean fewer survive the winter, and controlling their population is one important way to support natives. Many native ladybugs prefer to overwinter in leaf litter and mulch, Losey says, so leave those undisturbed in a part of your yard. There are other things people can do too, he says, such as growing plants in the carrot family (a major ladybug attractant) and avoiding pesticide use.

"A rising tide lifts all beetles," Losey says. "And we don't need to eliminate the invasive ladybugs, but we can all do things to help shore up native populations."