There are about 5000 species of stink bugs, shield-shaped insects that belong to the family Pentatomidae. One of the most notorious stink bugs is the brown marmorated stink bug (Halyomorpha halys Stål), a.k.a. BMSB, which The New Yorker called “the most destructive, the most annoying, and possibly the ugliest” of all the stink bugs, an invasive species that’s taking North America by storm … and not in a good way. Here’s what you should know.
1. IT MADE ITS WESTERN HEMISPHERE DEBUT IN PENNSYLVANIA.
Native to East Asia, the first BMSB specimens in the U.S. were collected in Allentown, Pennsylvania in 1998, but the bugs likely arrived a few years prior to that. (They may have come to the states in a shipping container, but no one’s sure.) Since then, they’ve spread to 43 states and will probably be continent-wide soon.
“It’s an incredible hitchhiker,” Dr. Tracy Leskey, an entomologist with the Agriculture Department’s Appalachian Fruit Research Laboratory, told The New York Times of the BMSB. Less than 10 years after it was identified in the States, it was in Switzerland and other parts of Europe, too.
2. IT TOOK YEARS TO IDENTIFY IT.
When the bugs were delivered to Karen Bernhard, an entomologist at Pennsylvania State University’s Extension Service, she had no idea what they were—and neither did anyone else. (Many assumed it was the native Euschistus servus.) It wasn’t until 2001, when Bernhard sent specimens to Richard Hoebeke, an entomologist specializing in invasive species who was then working at Cornell, that they were identified as brown marmorated stink bugs.
3. IT’S NOT CUTE.
After they hatch, the black-and-red nymphs go through five molts, growing into mottled, dull-brown bugs—up to .66 inches long—with white banded antennae and legs, alternating dark and light bands on the abdomen, and smooth, rounded shoulders. All of these features distinguish them from lookalikes like the brown, rough, and one-spotted stink bugs. BMSBs can live for up to eight months.
4. THEIR SPRAY HAS SOMETHING IN COMMON WITH CILANTRO.
Skunk. Old socks. Coriander. These are just some of the things the stink of the brown marmorated stink bug has been compared to. The two main chemicals responsible for the BMSB’s stinky spray are trans-2-octenal and trans-2-decenal. The latter is what gives cilantro its smell.
The chemicals in the spray might have a purpose besides scaring away predators: According to a 2016 study, they “inhibit the growth of bacteria”; the results of the study “suggest that brown marmorated stink bug aldehydes are indeed antibacterial agents and serve a multifunctional role for this insect.”
5. THEY EAT YOUR APPLES …
Brown marmorated stink bugs chow down on more than 100 types of crops. According to StopBMSB.org, apples, Asian pears, green beans, sweet corn, peaches, tomatoes, peppers, and Swiss chard are among the crops BMSBs pose the most risk to. Apricots, blueberries, broccoli, cauliflower, sweet potatoes, and turnips are also on the menu (though they’re less at risk).
To feed, the bugs pierce the skin of the plants with their mouthparts and drink the fluids, which in fruits like apples “results in a characteristic distortion referred to as ‘cat facing,’ that renders the fruit unmarketable as a fresh product,” according to a Penn State Extension article on the bugs. In 2010, mid-Atlantic farmers estimated that BMSBs caused $37 million in damage to apple crops alone. Some farmers of apples and other crops reported total losses that year.
6. … AND COULD INVADE YOUR HOME BY THE THOUSANDS.
Come winter, BMSBs are looking for a warm place to shack up so they can enter diapause, a hibernation-like state that lasts until spring (a.k.a. mating season). Outdoors, they’ll overwinter in dead trees—but often, they find their way into peoples' homes through open windows and doorways, in the gaps around window air conditioning units, down chimneys, and basically any crack they can find.
According to The New Yorker, “Studies have shown that, despite their relative heft, stink bugs can crawl through any crevice larger than 7 millimeters, which means that, no matter how much caulk and weather-stripping and patience you possess, it is virtually impossible to stink bug-proof a home.” But that doesn’t mean you shouldn’t try; experts recommend placing screens over windows and vents and making liberal use of caulk to patch cracks.
Once a stink bug has found a warm spot it likes, it will release an aggregation pheromone (which can linger for up to a year) that draws other BMSBs to the same area, where they’ll gather in sometimes staggering numbers: One study found more than 26,000 of them living in a Maryland home.
The good news is, beyond being a smelly nuisance, they won’t mate in your home or cause structural damage (though they might clog chimneys ... or your pipes).
7. ONCE INSIDE, THEY’RE HARD TO GET RID OF.
Some suggested stink bug removal approaches include knocking the bugs into soapy water, placing fly traps or double-sided tape in entryways, and spraying various concoctions (like garlic water) around your house. Vacuuming them up is also an option, though as the Penn State Extension article notes, “the vacuum may acquire the smell of stink bugs for a period of time,” so it might be best to avoid that tactic if your vacuum doesn’t have a bag you can easily toss.
A study showed that traps baited with the aggregation pheromone are only effective half of the year. And though foggers will kill stink bugs around your house, “it will not prevent more of the insects from emerging shortly after the room is aerated” and therefore “is not considered a good solution to long-term management of the problem.” Even expensive professional extermination efforts can be for naught.
Research by Virginia Tech has suggested that the most effective method of removal is to line a roasting pan with foil, fill it with soapy water, and place it in a dark room with a light above it to attract the bugs. According to a press release, this method—which was tested in 16 homes over a period of two years—“eliminated 14 times more stink bugs than store-bought traps that cost up to $50.”
8. THEY’RE PRETTY GREAT FLIERS.
In the home, stink bugs are lethargic, buzzing around clumsily thanks to diapause. But in the wild, they’re good fliers: Research has shown that, in flight mill tests, the bugs can fly 1.2 miles in a 24-hour period, and in field observations, they fly in a straight line at 6.7 mph. You can see one flying in slow motion here.
9. THEY’RE GENERALLY NOT HARMFUL.
BMSBs don’t sting or bite—their main defensive mechanism is their stinky spray. But some people can have allergic reactions, including rhinitis, conjunctivitis, or dermatitis, to the spray. The bugs aren’t toxic, so they won’t hurt your pets—though the chemicals in their spray might make your pets vomit or drool.
10. THEY MIGHT BE MESSING WITH YOUR RED WINE.
Not only do these pests feed on grapes, but they can end up in the mix as grapes are turned into wine, where the bugs give off stress compounds that affect the quality of the vino. Researchers at Oregon State University placed live and dead stink bugs on wine grapes and measured the stress compounds the insects released as they and the grapes were squeezed during the winemaking process. According to a press release, “They found that pressing was a key step in the release of two of the most common stress compounds—tridecane, which is odorless, and (E)-2-decenal, which produces an undesirable musty-like, coriander or cilantro aroma.” Red wine was more affected than white, maybe because the grapes are pressed at different points in the production process. The researchers found that more than three stink bugs per grape cluster resulted in contaminated wine.
11. THEY LEAVE TRACES OF THEIR PRESENCE ON PLANTS.
Scientists at Rutgers University recently discovered that they could detect the eDNA (or environmental DNA—things like skin flakes, scales, exoskeletons, or fecal matter) of brown marmorated stink bugs in the water farmers used to wash their produce before the crops go to market. They visited two farms—one in New Jersey with a known stink bug infestation and another that was just outside the bugs’ range in New Hampshire—where they both tested water and set traps for the bugs. As expected, they found stink bug DNA at the Jersey farm … and they found it at the New Hampshire farm, too. There, on the last day of testing, an immature stink bug ended up in a trap—visual confirmation of what their data was telling them. They hope that farmers can use the test to detect stink bugs before there’s a full-fledged infestation.
12. ONE OF ITS NATURAL PREDATORS IS A PARASITIC WASP THAT JUST MADE ITS WAY TO THE STATES.
In the U.S. the BMSB has few predators—so when scientists were looking for a way to combat the pests, they went to Asia. There, the stink bugs are kept in check by samurai wasps (Trissolcus japonicus), a tiny, stingerless parasite that lays its eggs in the stink bugs’ eggs, where its larvae eat the contents before emerging as wasps to continue the cycle. Sixty to 90 percent of BMSB eggs in Asia are parasitized by the wasps.
Scientists brought some of the wasps back and began testing to see if they would be a good candidate for release in the states. But before they could release any, the wasps showed up on their own, in Maryland in 2014. (Genetic testing showed that they weren’t escaped wasps that the scientists had been studying.) According to Science, “Although in laboratory tests it has parasitized some eggs laid by native species, [the wasp] has shown a strong preference for brown marmorated stink bug eggs.” Still, scientists are proceeding with caution: Though they can release the wasps in states where they’ve already been found, there are rules and regulations to follow and permissions to get before they can be released anywhere new.