They creep into gardens, trees and crops in the field. They find hiding places through the winter, then re-emerge to infest again. As late summer becomes fall, brown marmorated stink bugs will soon be seeking entry points into Maryland homes in search of a haven for the winter.
The crawling, flying, shield-shaped insects, known to entomologists as Halyomorpha halys crashed the United States from China in the 1990s and now infest much of the continent, particularly the Mid-Atlantic region, where they're more populous than anywhere else.
There isn't much one can do when the uninvited houseguests come calling, said Randy Low, a volunteer educator with the Baltimore County Master Gardeners who often speaks on the subject.
"These critters have been a major challenge for the experts," Low said. "My advice is this: Think prevention. Seal your house the best you can. And keep your fingers crossed."
The pervasive pests, a species native to China, Korea and Japan, arrived on American shores as stowaways on a cargo ship in Philadelphia. Lacking any natural predators, they proliferated quickly, then migrated throughout the Mid-Atlantic and beyond, mostly by "hitchhiking" inside cars and trucks.
While stink bugs don't bite, raid the pantry or munch clothing, they do have one problem: They stink.
Voracious eaters, the bugs have bedeviled farmers, gardeners and pest management researchers alike, feasting on everything from apples, peaches, soybeans and tomatoes to Asian pears, flowering dogwoods and lima beans.
"They'll eat anything," said Tracy Leskey, a research entomologist with the Agricultural Research Service of the U.S. Department of Agriculture.
Leskey was the first director of StopBrownMarmonatedStinkBug.org, a research initiative that combines the efforts of more than 50 scientists from 10 institutions in a mission to combat the pests.
The size of the bugs' infestation and their harm to crops varies from year to year, researchers say, depending on a variety of circumstances, but when they're bad, the effects can be devastating.
In 2010, Leskey said, growers who worked with her research consortium lost between 50 percent and 100 percent of their peach crops, and when they weren't demolishing tomatoes, peppers, soybeans and corn, the bugs were doing $37 million in damage to apple crops in the Mid-Atlantic alone, according to the U.S. Apple Association.
On a recent evening, Low gave a talk on the brown marmorated stink bugs at the Hereford branch of the Baltimore County Public Library, one of hundreds of similar presentations that Master Gardeners in Maryland offer members of the public each year.
The University of Maryland Extension, that institution's agricultural outreach arm, founded the Master Gardeners program in 1978 and currently operates it in 20 branches serving 22 counties in the state.
The gardeners and farmers at the talk seemed more concerned about a less catastrophic but equally annoying stink bug practice. After spending the summer feasting on fruits, vegetables and ornamental plants, it turns its attention to moving indoors for the winter.
Anyone who lives in a wooded area or near gardens or orchards risks having a swarm of the creatures enter through uncovered vents, torn screens, loose soffits or unsealed points of entry around pipes or cables. It could be just a few bugs or it could be thousands.
The bugs aren't harmful to humans, but they can be unsightly and unnerving, and they sometimes nest in appliances and ruin small engines.
For reasons researchers can't explain, the busiest time for home invasion is usually the third week of September.
Stink bugs get their name from their defense mechanism, a chemical they can release to keep from being eaten by birds or lizards in their native land. People who touch, frighten or step on the bugs can describe the cilantro-like smell.
"One fell from a ceiling light into my coffee cup, and I drank it," said Vince Adwan, a landscaper who cares for a farm in Monkton. "I used to love cilantro. Now I can't go near the stuff."
Adwan finds the bugs' hardiness a bit scary, but he and others take comfort in the strides researchers have made.
In the months after the massive crop kill in 2010, the USDA gave a 10-year grant to a stink bug work group Leskey was leading, transforming it into a multi-institution force.
With Leskey as director, and University of Maryland entomologists such as professors Galen Dively and Michael J. Raupp on board, StopBrownMarmoratedStinkBug (stopbmsb.org) established four main objectives: getting to know the bug's biology, ecology and behavior; developing management strategies; integrating tactics to make its management sustainable; and publicizing information.
Using pheromone-baited traps, they observed the bugs on selected farms, and developed a nuanced profile of the brown, mottled insect that uses a thin proboscis to penetrate the outer layers of about 170 kinds of native plants.
Efforts to find effective pathogens and parasites have had mixed results. So have attempts to trap and lure them elsewhere.
Researchers developed organic pesticides that seemed to kill the bugs, only to learn two or three days later that most were still alive.
The team has helped farmers develop strategies such as growing "waste crops" around an orchard's margins and using a clay-based spray on plants. (The bugs hate the texture, but it washes off in the rain.)
Nature has opened up perhaps the most promising avenue: A number of native animals have finally figured out that the stink bugs or the bugs' eggs "make a tasty meal," Leskey says, including katydids, spiders and several types of songbird.
"We're getting more help these days from natural enemies," she said.
In Hereford, Low told listeners not to count on pesticides, the best of which only work for a brief time. Instead, she recommended taking steps to keep the bugs out such as "tightening up the house" with caulk, new screens and other insulating materials. And if bugs do get in, shop-vacs suck them up nicely.
Finally, Low held up a plastic soda bottle with the spout end punched in.
Fill it with soapy water, she said, then flick the pests into it from your walls or ceilings, and they'll fall in, struggle and drown.