Seeking Shelter

Asian lady beetles often head inside as winter approaches. But you may want to resist the urge to squash these helpful bugs

November 03, 2006|By Frank D. Roylance | Frank D. Roylance,Sun reporter

So who's that tap, tap, tapping on your window pane?

If it's a warm day in this autumn season, the visitor could be the multicolored Asian lady beetle. The pesky import gobbles scads of garden pests every year, but expects free winter housing in return.

"I was working at home and noticed these things crashing into my front window," said University of Maryland entomologist Mike Raupp. "They were quite numerous on the southern exposure of the house, where it was warm."

Later, walking on campus at College Park, Raupp spotted scores of them sunning themselves on the columns of south-facing buildings. The warm sun keeps the cold-blooded insects active - but what they really want is shelter for the winter.

"For the next several weeks, deep into November, on bright sunny days we'll see these ladies aggregating," Raupp said. "Normally, this would occur on rocky outcrops in the mountains. But there's a paucity of rocky crags in the D.C. metro-Baltimore area."

So they settle for buildings. And homes.

And then they crawl inside, through any tiny gaps and cracks they can find. Some end up dead on a window sill. The lucky ones will settle into a chilly but protected spot where they can sleep until a warm day in early spring wakes them up.

But they may also encounter an intolerant human, make a nuisance of themselves and meet an untimely end.

And that's too bad, Raupp said.

"This thing is enormously beneficial because it eats so many aphids" and other plant-sucking pests, he said. A lady beetle can eat 1,200 aphids during its two-week larval stage. As an adult, it may eat 250 more every day.

It's an "eating machine," Raupp said.

There are downsides, of course. Aside from their penchant for home invasion, Asian lady beetles can bite. Raupp describes the sensation as "less than a Doberman - more of a tickle."

They also have a nasty habit called "reflex bleeding" - oozing droplets of smelly, yellow-staining blood from their leg joints when stressed. Or smashed.

It's also possible that their aggressive feeding is displacing native species of ladybugs. "This is a major controversy" among entomologists, Raupp said.

The multicolored Asian lady beetle is, after all, an invader - or, more precisely, an introduced exotic.

Formally known as Harmonia axyridis, the critter was brought to the United States from Japan in many varieties as early as 1916 as a biological control agent. It was released in the wild to eat such injurious plant pests as aphids, scales and psilids.

Even the U.S. Department of Agriculture joined in the practice, freeing Asian lady beetles in Louisiana and Mississippi in 1979 and 1980. They ate their way to happiness wherever they went.

By 1994 they were in Alabama, Georgia, South Carolina and Florida. Now they're well-established in Maryland and across much of the United States, as far as Oregon.

They're called "multicolored" for good reason. The beetles' hues range from near scarlet to pumpkin orange - one reason, along with their autumn appearance, that they're also called "Halloween beetles."

And usually, but not always, they sport black spots on their "shells" - actually wing covers. There may be as many as 22 spots, or none at all.

The Asian bugs are most easily distinguished from native lady beetles by the W- or M- shaped marking on their thorax. Which letter depends on which way you view the bug.

But they behave differently. "The native beetles are much more likely to stay where they belong, outdoors, and find wintering spots in the landscape - [perhaps] a hollow log - rather than take a shot at home invasion," Raupp said.

The Asian variety greets the world in the spring as a tiny yellow egg, attached to a leaf. The egg hatches in three to five days, yielding the spiny larva, which eats like crazy for 12 to 14 more days.

The larva then enters a pupal "resting" stage for five or six more days before emerging as the more familiar flying, mating, egg-laying adult.

Unlike many insects, which may spend the winter at the egg stage (the praying mantis), or as larvae (the woollybear caterpillar), lady beetles overwinter as adults.

They are also unusual for their longevity, surviving as adults for two to three years, which is why they are so desperate these days to find a nice house or attic to squat in for the winter.

But even if they survive their encounters this fall with homeowners and their cats, they face more hazards ahead.

"If it happens to be your attic, let's say, then on a nice warm day in February, perhaps, they would emerge in advance of their normal time and find a way to a southern picture window, where they could be a bit of a nuisance. It's a problem in late winter and spring," Raupp said.

The solution is not chemical warfare, Raupp said. These bugs are too beneficial in the garden. It's also a bad idea to smush them, because they may stain the drapes.

It's better to sweep or vacuum them up and transfer them outdoors.

"I put them in my tool shed, where it's nice and chilly, and they can pretend it's a rocky, craggy outcrop where they'd like to be," Raupp said. "If they keep on schedule, they'll emerge [in spring] and move into the garden and eat aphids."

frank.roylance@baltsun.com

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