Over the past several years, the invasive brown marmorated stink bug has found hospitable conditions in our houses, which are appealingly warm during Western Washington’s cold, wet winters. They’re a real nuisance, not only to certain crops, but also to humans.
It’s easy to feel as though you’re seeing stink bugs everywhere — clumped together on windowsills, buzzing around your ceiling lights or in your garden. But are they all invasive stink bugs? Maybe not.
Brown marmorated stink bugs are one of three bugs that can confuse the untrained eye, along with squash bugs (a difficult-to-eradicate pest) and western conifer seed bugs (harmless though occasionally annoying).
“Stink bugs, squash bugs and western conifer seed bugs are not all in the same family, but they’re in the same order — true bugs, Hemiptera,” said Adrian Marshall, a Yakima-based post-doctoral research associate with the U.S. Department of Agriculture’s research service whose areas of specialty include brown marmorated stink bugs. “It’s a huge group. It includes leaf hoppers, aphids and cicadas. It’s any bug that has four wings and a piercing mouthpart rather than a chewing mouthpart.”
Wide, brown-gray, loves to cluster
There are over 50 types of stink bugs (family Pentatomidae) zooming around Washington, but only a handful cause problems, Marshall said. Stink bugs are also called shield bugs because of their wide, five-pointed shape. Brown marmorated stink bugs, which grow to half an inch, are named for the brown-gray marbling (or marmoration) on their backs. These dapper bugs sport black-and-white banding around their sides, legs and antenna.
The brown marmorated stinkbug is not native to Washington but entered the country on the East Coast around 2012 before spreading to our state within four or five years, Marshall said. The stink bug invasion posed a concern to the Northwest because of the way it devastated tree fruit crops on the East Coast, but it hasn’t been as destructive here.
It is, however, an irritant to humans. Native stink bugs spend the winter under fallen leaves, but the brown marmorated stink bug has other plans. Drawn by house lights, heat-seeking stink bugs find holes in screens and cracks in walls or floorboards and move inside. Once a stink bug finds a place to get cozy, it calls its friends to share the good fortune by emitting an “aggregation pheromone,” Marshall said, so one stink bug can soon become hundreds or thousands.
“There are stories on the East Coast of people finding tens of thousands of stink bugs and they have to sweep them away with a broom,” Marshall said. “We’ll see one wave coming in the fall and then we’ll see another wave as they’re all leaving because they go back outside in the spring.”
Deter stink bugs from entering your house by repairing holes in screens and sealing cracks in floorboards, Marshall said. Shade windows at night and turn off lights where possible. Avoid squishing the bugs because, as Marshall succinctly stated, “It stinks.” Instead, create a trap by placing a bucket of soapy water under a bright light; stink bugs will fly into the light and fall into the bucket. Crawling stink bugs can be brushed into a container and flushed down the toilet.
“If you can submerge them in water the smell won’t come out, though the chemical they emit is not harmful,” Marshall said. “It’s better to kill them because they’re an invasive species than to leave them alive. They’ll just keep reproducing.”
Long, gray-brown, deadly to squash
Squash bugs belong to family Coreidae, or leaf-footed bugs, so named because of the small, leaflike appendage on the back legs, Marshall said. Dark gray-brown or black adult squash bugs are longer and narrower than stink bugs and grow to three-quarters of an inch long. Light gray nymphs look like small adults. You may find the youngest, soft-bodied nymphs clustered on leaves or fruit, sucking the juices out of any cucurbits plant, which includes squash, zucchini, pumpkins, melons and cucumbers. However, because squash bugs haven’t been a major pest for commercial growers, there’s not much research to help the home gardener, Marshall said.
“There are homeowner-approved chemicals to use for squash bugs, but a lot of people don’t have the time or the resources to implement them, so they end up losing their squash. Another problem is they don’t realize they have squash bugs until too late,” Marshall said. “Some people have just stopped growing cucurbits altogether because of this pest.”
Adult squash bugs spend the winter under leaf litter or other garden debris and can survive under snow. In spring, they emerge to find cucurbits plants and lay eggs on the undersides of leaves. Flightless nymphs stay put and feed on the plant until adulthood. You may notice yellow, wilted leaves or see withered fruit on the vine. That’s because squash bugs secrete a saliva-borne toxin that hastens the demise of your cucurbits plants, Marshall said.
“The main point of defense is to look for the first generation of adults, because those adults won’t do a lot of damage but the nymphs that come from them will,” Marshall said. “Concentrate your efforts on that first wave — finding the adults and the eggs and removing them. … The infestations you have later in the summer are from that first generation.”
Red eggs are easily visible against green leaves near leaf veins. Remove eggs by lifting them off with duct tape, Marshall said, or pinch the eggs to kill them. Pluck adults off vines and drop them in soapy water. If you squish a squash bug, it won’t smell good, but it won’t stink like a stink bug, Marshall said, though it may release a short-lived “alarm” pheromone telling other squash bugs to avoid the area. If you have a history of squash bugs, burn plant litter or destroy it with a mulcher and ask your neighbors to do the same, Marshall said.
“If people are having problems with squash bugs, report it to the Washington State Department of Agriculture so that the people who fund research can know that it’s a problem and hopefully solutions can be found,” Marshall said.
Long, reddish brown and (mostly) harmless
Western conifer seed bugs (also family Coreidae) grow to three-quarters of an inch long. Marshall said these “really pretty” bugs are narrow rather than wide and sport a “light brown to dark, woody reddish color.” They’re found mainly in conifer forests, where they feed on pines and firs like the Douglas fir.
“The good news is that they’re native and they don’t cause any damage to tree health, so they’re not a pest by any means,” said Marshall. “They feed on tree seeds and even then it doesn’t cause any forest problems. The only problem is that, like the brown marmorated stink bug, they come indoors.”
They spend the winter nestled under tree bark. However, our houses are also made of pine, said Marshall, so some seed bugs are attracted to our dwellings, especially any structure near a forest. Drawn by lights, seed bugs will find a way inside “and it will just seem like the right place to be,” Marshall said.
To discourage western conifer seed bugs from becoming your winter guests, take the same steps as you would for stink bugs. If you find one inside, take it outside (though it may come back) or just leave it alone.
“They do emit a different smell than stink bugs but it’s nowhere near as strong or unpleasant. That’s only if you grab them,” Marshall said. “It’s a defensive chemical so if you make them defend themselves, that’s all they’ve got.”
None of the three bugs pose any direct harm to people. Their mouthparts aren’t made for biting, and they can’t sting. They aren’t toxic to humans, even if — horrors! — they’re accidentally ingested, although stink bugs will release a foul-tasting liquid that can irritate the mouth or upset the stomach. Stink bugs and seed bugs won’t damage homes and squash bugs are only interested in your garden.