You share your home with more than pets, partners, roommates, or family. Despite our best efforts to willfully ignore or scour away their presence, there are many other lives in our homes. Many are arthropods that are residents, or nearly so, like Giant House Spiders, and others are only part-time houseguests. I’ll never forget slumbering by the fire one fall only to wake to the stings of the yellowjackets that had nested inside our previously smoke free chimney.
Others are more benign, like stink bugs, which you might have noticed crouched on the edges of your home this fall.
In particular, I have noticed one species a lot more this year: the Brown Marmorated Stink Bug, Halyomorpha halys.
A native of China, Japan, and Korea these insects were first documented in the U.S. in Allentown, Pennsylvania in 1998 and had spread across the country to the Pacific Northwest by 2004. I can’t quite remember when I first noticed one of them (sometime post 2017 when they showed up in King County), but it was definitely in the fall when they had started to move indoors.
You’re likely familiar with insects in the family Pentatomidae, the shield bugs or stink bugs depending on where you are from, of which there are nearly 5000 described species worldwide and about 50 in Washington State. They are fairly obvious because they are slow moving and sometimes quite beautiful. This family is part of the order Hemiptera, which is a large diverse group of insects like aphids, cicadas, and even bed bugs all of which have piercing mouthparts they use to puncture and slurp through. If you have some snippy entomologist friend that tells you that “not all insects are bugs, but all bugs are insects,” they’re referring to this order, also called the “true bugs.” Even as someone fascinated by taxonomy it’s hard to not roll my eyes at stuff like this.
If you searched “stink bug” on Google right now your first hits would probably revolve around pest management and invasive species, mainly because of the Brown Marmorated Stink Bug. While I take issue with this because it means that many people will immediately react with fear, paranoia, and violence when they see anything they perceive as a “stink bug,” there’s a good reason for concern. Brown Marmorated Stink Bugs pose a threat to agricultural and ornamental plants.
Many stink bugs are generalists and feed on plants through their straw-like mouthparts. They readily drink down agricultural crops, not only blemishing plants and fruit, but destroying seed production. They are also extremely difficult to control with chemicals because they don’t easily ingest topically applied pesticides. If you aren’t a farmer, (which I can assume most folks reading this are not) this might be a major concern. But I know all of you eat food and many of you have gardens, which are also on the menu.
Part of the concern is that Brown Marmorated Stink Bugs are on the rise, enjoying the benefits of climate change in the perfect storm of “I told you so” we’ve heard from climate scientists for years.
Climate change makes us all the more vulnerable to introduced species. If you’ve been paying attention to Pikes/Pines, the major concern with introduced species is that they often live outside the checks and balances an ecosystem relies on. Aside from another introduced wasp, there are no other known controls aside from pesticides (which are indiscriminate) that we can rely on to keep Brown Marmorated Stink Bug populations at reasonable numbers.
Stink bugs in general are extremely good at sneaking into cracks and hiding out, which is part of the reason non-native ones can spread so well. Our habits of commerce are good vectors for a bug hopping a ride on a shipping container or in a crate.. Brown Marmorated Stink Bugs are particularly easily spread this way because they naturally move toward warmer places to hibernate in winter.
While I have never experienced a full fledged invasion of Brown Marmorated Stink Bugs in any place I have lived, I maintain one fact: they are not directly harmful to humans but instead an annoyance in our homes. We don’t currently live in a place where Brown Marmorated Stink Bugs can produce multiple generations within a year (which is their average lifespan), so they can’t amass quite as much as they can in other parts of their range in the US. But I can also understand why having hundreds, in some cases thousands, of them inside your house is problematic. I wouldn’t be down.
Their name isn’t an exaggeration either. When they are bothered or even crushed, they emit a far from pleasant stink. This varies between species and even the age of the bug. It has a musty, acrid odor that I am not eager to smell regularly.
Despite my hesitancy to cosign warfare against all Brown Marmorated Stink Bugs, there are real reasons to be concerned about emerging numbers of introduced species. I personally don’t have great concern about soybean crops (I do care more about our local apples and cherries), but I do care about overall ecosystem health.
The biggest worry with species expansions like this one is that we don’t always know what will happen when they suddenly show up. And in some instances, like those of Chestnut Blight or Emerald Ash Borer, we had already lost the battle before we really knew what was happening.
As generalists we’re more likely to have a persistent, troublesome pest in the Brown Marmorated Stink Bug rather than a species destroying curse. But that doesn’t mean a generalist can’t be a vector for plant diseases we are yet to understand. It’s entirely likely that we’ll lose all of our Oregon White Ash trees in the next few decades as Emerald Ash Borers work their way west. I’m not eager to see any more situations where we lose entire populations of once common species, so I can understand why there’s some attention and focus on this particular bug.
Ultimately, I want people to live lives filled with curiosity, excitement, and empathy for the more than human world, even in highly altered places like the Hill. It’s sad that children grow up fearing arthropods, not because stinging and biting ones don’t deserve wary respect, but because it demonstrates a lack of connection. Brown Marmorated Stink Bugs might not be the houseguests we want, but we might end up with them anyway. I find them pretty cool looking, so if seeing one sparks anyone’s interest in insects, I’d be ok with a few bunking down in my house. But not hundreds. And definitely not thousands.