An Unwelcome Winter Visitor

One of the things I like about my part of the country is that Mother Nature’s extremes are relatively rare. We don’t need to worry about earthquakes, wildfires, tornadoes, mudslides, or rivers overflowing their banks. I’ve only seen hail twice in my life, and they were tiny. Hurricanes don’t often make it this far north. We experience all four seasons but in a fairly reasonable fashion: Average July/August daytime highs are in the low to mid 80sF, and in the high 30s-low 40sF in January/February. When we do have extremes – either above 90 or in single digits F – they last days rather than weeks. And radon is such a complete non-problem here that the word isn’t even part of the real-estate lexicon at all.

When it comes to annoying or destructive wildlife we really can’t complain much either. There are the usual suspects (mice, rats, voles, squirrels, rabbits) although some neighborhoods do have deer (thankfully not mine.) Unlike our compatriots in the South, we are spared dealing with scorpions, fire ants, palmetto bugs, or drywood termites. Not that we are pest-free: the nasty little Asian tiger mosquito, Aedes albopictus, showed up here about 15 years ago and demonstrated that the only thing worse than a mosquito is a mosquito that bites instead of only at dusk and dawn. But all in all, I have a pretty good game plan regarding most bugs I’m likely to encounter.

Which is why I was taken by surprise a couple of evenings ago when I spotted a very large black Something in the upper left hand corner of my shower stall. Now, while I do not shriek and jump up on chairs at the mere sight of an insect indoors, neither am I a fan of them. My philosophy is that ALL members of the class Insecta or order Arachnida belong strictly on the outside of my “building envelope.”

A quick glance was enough to determine that the newcomer invader was not a hornet, wasp, bee, moth, fly, cockroach, mosquito, or spider – and therefore not a physical or immediate emotional threat. My first guess was a beetle of some sort. It being at ceiling height, and me having no inclination to get up close and personal, I fetched my binoculars. (Don’t laugh, it worked.)

Hm. What looked like black was more like very dark brown. Body shield-shaped, with a row of white spots along the outside edges. Six legs, two antennae. Into the back of my mind popped the name of an insect I’d read about several years ago as having appeared in this area but had never seen in person: the brown marmorated stink bug. All I remembered about it was that they, well, stink and that people absolutely loathe them because of it. Armed with my mental picture, I fired up Google Images and typed in “stink bug.”


Within the space of 30 minutes I became an “expert” on the brown marmorated stink bug, Halyomorpha halys … or BMSB for short. It is, as I suspected, a beetle. Here’s the good, the bad, and the useful – should you ever have one of these unwelcome indoor visitors which is becoming, unfortunately, increasingly more likely.

 The Good

  • Stink bugs do not reproduce indoors. This, as you can imagine, came as a massive relief.
  • They do not bite or sting humans or pets. Ditto.
  • They do not damage structures or seek out human food or materials. They are strictly plant-eaters.

The Bad

  • Stink bugs are the skunks of the insect world. When attacked, harassed or otherwise disturbed they emit a strong noxious odor that has been described in various words but is always some variant of “disgusting”, “horrible”, “skunky”, “burning rubber”, “rancid cilantro with an undertone of rotting garbage”, etc. And the smell can linger in the air and on surfaces for hours.
  • Insecticides don’t kill stink bugs; it just annoys them. Trust me, you don’t want to do that.
  • Stink bugs have no natural predators in the USA… yet.

The Useful

The BMSB was accidentally introduced here from Asia during the mid to late 1990s, no doubt in a shipment of cheap mass-produced something-or-other from China or Japan. The first specimens were found in Allentown, Pennsylvania, in 1998. Because of the complete lack of predators it has spread rapidly during the last 20 years and is now found in 43 states as well as the two eastern provinces of Canada, and has become a major pest of agricultural crops. It is expected to be resident throughout the entire North American continent before 2025.


The upper map shows the distribution of the brown marmorated stink bug in 2013; the lower map shows its range the following year. It went from being a “nuisance pest” to an “agricultural and nuisance pest” in five more states in only a single year, and expanded its range into two new states as well.

The BMSB begins life as one of a cluster of eggs laid on the underside of a leaf – pretty much any kind – from May to early August. After it emerges as a nymph it begins to feed…and feed.. and feed on, again, pretty much anything that’s green and growing but it is particularly fond of fruits. Some researchers say that buddleia is especially attractive to stink bugs which, if true, is a good argument for keeping butterfly bushes well away from your house.

As they reach adulthood in early autumn they begin to seek out a nice place to overwinter. To a stink bug, our houses serve this purpose admirably. Any opening, crack or crevice larger than 1/8 inch is a stink bug doorway during September and October. Holes in window screens, unscreened roof or wall exhaust fan vents, plumbing stacks, gaps in siding or window frames or flashing, doors that don’t seal tightly on all four sides… and in they will come.

The operative word is “they” because a stink bug doesn’t like to spend winter alone. As soon as it finds a good spot, it sends out a special pheromone to alert all its friends and relatives to come on over and socialize. It’s the insect equivalent of posting a frat party location on Facebook. To a BMSB, a decent winter party is at least a few hundred. Or a few thousand. There is no such thing as just one stink bug inside your house during winter. They all get comfy inside a wall or in the attic and go into what’s called diapause. Diapause is a type of dormancy, hibernation, or torpor. The stink bugs don’t do anything, they just wait until the environment tells them it’s spring and time to go back outside and make babies.

The problem (for us) starts when we get those lovely nice unseasonably warm winter days, maybe in the 50s or even low 60s in, say, January. (Just like we had last week here!) The BMSBs feel the change in temperature and think it’s spring. Problem is, they’re still pretty punchy and groggy and it’s easy for them to get confused and come through interior wall openings into the house rather than outdoors. The inevitable openings around heating baseboards and ceiling registers and plumbing pipes are easy for them to get through because gaps only need to be bigger than 1/8 of an inch.

Once inside a room they “realize” their mistake but don’t know what to do about it. (These are bugs, not Stephen Hawking.) This may lead them to fly around aimlessly, scaring the daylights out of people and usually following one or both of their basic diapause instincts: (1) to congregate with others of their kind, and/or into some space that makes them feel secure; and (2) to get as far off the ground as possible. That’s why you don’t usually see stink bugs in basements, even if they initially got in that way; they will head for the wall framing and travel to an upper level instead. It also explains why I saw my bathroom visitor in the corner of the wall and ceiling; that’s as high as he could manage to get.

Sometimes the bugs can’t all find their way back outside when spring does actually come, in which case they will do the next best thing and come out into the house interior. Great.

Stink Bug Management (or, How Not to Get Skunked)

If you see one or more of these things inside your house, do NOT give in to the perfectly natural urge to swat, spray, or otherwise send it dramatically to the Great Beyond. The best tool is a canister vacuum without the floor or crevice tool on the end of the wand. Even if the bug is at ceiling height you should be able to reach it/them. Basically just point the business end of the wand (make sure to use the strongest suction setting) at the bug(s) and remove them that way. Do not turn off the vacuum until you’re completely done; you don’t want any laggards to crawl or fly back out of the open end of the wand. If you have an old, or extra, vacuum – rather than your pricey Miele or Aerus or Sebo – so much the better, because depending on how irked your unwelcome vistor gets, the vacuum itself may not escape un-stunk.

It is a good idea to immediately dispose of that vacuum cleaner bag because you probably don’t want a stinky vacuum cleaner. And the more bugs you’ve vacuumed up, the more likely that is to happen. Luckily I have an old but trusty little Sharp EC7311 that I’d been using only to vacuum my car; today I ordered a box of 20 replacement bags for it, just in case.

The trick is to keep the stink bugs from getting into your house in the first place. This is not easy but it’s well worth it to try. Remember the 1/8” rule … typical ¼” mesh screening is not small enough. Invest in some good silicone or latex caulk. However, do not do this before, say, June! You want any stink bugs that have been overwintering in your house to be able to find their way outside when the time comes. If you close up all the gaps during the winter months, they’ll have nowhere to go in spring but your rooms, and you don’t want that. Start sealing everything up from the outside in July, while the BMSBs are otherwise occupied in damaging your landscape.

Some pest control manufacturers or services will offer to spray your exterior walls against stink bugs in late August. Unfortunately although it sounds good (as a DIY you’d need to get all the way up to the soffits, fascias, etc – not the safest idea) it’s often a waste of money.  The Pennsylvania State University Extension Service, which probably knows more about stink bugs than anyone and has no commercial agenda to push, says this about such treatments:

Exterior applications of insecticides may offer some minor relief from infestations when the task of completely sealing the exterior is difficult or impossible. Applications should be applied by a licensed pest control operator in the fall just prior to bug congregation. Unfortunately, because insecticides are broken down by sunlight, the residual effect of the material will be greatly decreased and may not kill the insects much beyond several days or a week.

Which brings up something else about the BMSB: it congregates (and looks for entry points) on south and west facing exterior walls especially. It’s because those walls are warmest on those autumn afternoons. Obviously those exterior walls, if sprayed, also get the most sun and will break down any application of insecticide the fastest … making the effort the least effective where it should count the most.

The excellent Penn State page also has this advice for stink bugs encountered in the house:

It is not advisable to use an insecticide inside after the insects have gained access to the wall voids or attic areas. Although insecticidal dust treatments to these voids may kill hundreds of bugs, there is the possibility that carpet beetles will feed on the dead stink bugs and subsequently attack woolens, stored dry goods or other natural products in the home. Although aerosol-type pyrethrum foggers will kill stink bugs that have amassed on ceilings and walls in living areas, it will not prevent more of the insects from emerging shortly after the room is aerated. For this reason use of these materials is not considered a good solution to long-term management of the problem. Spray insecticides, directed into cracks and crevices, will not prevent the bugs from emerging and is not a viable or recommended treatment.

So you can skip the usual products like Ortho Home Defense, or borax, as well. Just rely on a bag-type vacuum cleaner.

The question remains as to how and why my unwelcome visitor (and his inevitable but as yet unseen friends) got in. I do have a few clues. For three weeks this past October, the original white-painted wood siding was removed from my house and replaced by new vinyl siding in a luscious shade of dark chocolate brown. There were several days in which I’m sure there were entrance opportunities for stink bugs seeking their own version of “snowbirding” during prime invasion time.  Also, although the new siding color will be wonderfully effective at hiding dirt or any errant artillery fungus spores left in nearby soil from past wood mulches, it also makes the long west wall and short south wall of my house absorb much more solar heat than the white wood did… and thus it is a much stronger stink bug magnet.

The Michigan State University web page on stink bugs says this:

In older homes with wooden clapboard siding, their entry can be reduced by caulking or sealing cracks and crevices on the exterior. No amount of caulk will keep the beetles out of homes with vinyl siding because vinyl siding and soffits are “hung” or loosely nailed to permit the vinyl panels to expand and contract with changing temperatures. Even with wood siding, complete sealing with caulk can be difficult, if not impossible, to accomplish in some homes.

I have to say that this is my second vinyl-sided house and I never had stink bugs in the previous one, despite having a long south facing wall. That siding was a lighter color (more like a Wedgwood blue), however. So there is no doubt an element of luck in whether any given vinyl sided house ends up with a stink bug infestation or not.

It’s on my list to see how (or if) my bathroom and kitchen exhaust fans are screened on the outside. I suspect they’re either not, or that the screen has openings larger than 1/8”.

More good advice from MSU:

If sealing the exterior walls does not help, then caulking around outlet and switch boxes, ceiling fixtures, heat ducts and other openings in interior walls may at least keep the bug in the walls and out of the living space.

This is probably the most practical approach or better yet, done in combination with sealing the exterior as much as you are able.

There is a faint light at the end of the tunnel, though, because scientists are working on releasing a small Asian wasp that parasitizes the BMSB’s eggs; it has the evocative name of Samurai Wasp. Trissolcus japonicus is extremely tiny (think sesame seed) and has no interest in humans but it’s what keeps stink bugs under relative control in its native habitat. Once established, it’s hoped that these wasps may be able to reduce the burgeoning North American stink bug population by as much as 90%. These little guys certainly can’t come too soon for many farmers and homeowners!

I feel a bit sad, though, that from now on any unseasonably-warm winter days are not going to be greeted with the same unmixed pleasure as before: I will now always be on the alert for any interior-invading stink bugs which will be very un-welcome winter visitors.

  11 comments for “An Unwelcome Winter Visitor

  1. Betty McCullough
    February 9, 2019 at 9:26 pm

    Excellent piece – thank you for all your research. While I was reading your information, I got up and went to the kitchen and saw my 1st stink bug. I had an empty plastic bottle on the counter so trapped the stinker and now he is locked in and in the recycle bin. Thanks to you I will be on the look out for his friends.

    • February 16, 2019 at 2:54 pm

      Wow, it really is true that “timing is everything”, LOL! I’m sorry about your unwelcome visitor but glad that my post arrived just in time to be of help. 🙂

  2. February 10, 2019 at 9:41 am

    Very informative!
    We’re just a little North of ground zero so it’s been a few years since the first one showed up, and for us it has fortunately never reached invasion status. A few each winter and usually I just grab them with a tissue and flush them on their way. I wonder if we’re just not that sensitive to the stink? I’d call that a blessing 🙂
    If you want to know who your next pest will be check out the spotted lanternfly. Another one to thank Pennsylvania for….

  3. February 10, 2019 at 10:09 pm

    They look like the native stink bugs here. The natives are not very common, and seem to prefer elms an some specie of pine; more specifically, Monterey pine. They are not too terribly noxious. This new one looks just like it, but sounds worse. I have not encountered it yet. It is supposed to be a ‘nuisance’ here, but California is a big state.

    • February 16, 2019 at 3:02 pm

      A correspondent of mine in Texas sent me a photo of what they’ve always called Pumpkin Bug or Squash Bug, which is similar but strongly limits its cuisine to the squash family. The BMSB is not nearly as fussy an eater (sadly.) And squash/pumpkin bugs don’t overwinter in structures; they stay outdoors as any well-brought-up insect should do!

      • February 17, 2019 at 1:33 pm

        It seems that many of the most objectionable insects are bugs. The box elder bug is a rather bothersome one here, only because it is so prolific in season. A friend who lived in an apartment building in Aptos had a serious problem with bed bugs that were very established in the building. Even if not the most destructive of insects, bugs seem like the most annoying.

  4. February 11, 2019 at 1:17 pm

    I have not seen them in our garden yet, thank goodness.

  5. Adine
    February 12, 2019 at 4:03 pm

    Bag-type vacuum cleaner! How simple, how clever. I kept thinking that one of those electric fly swat killers would do the trick of killing your unwelcome visitor but I like your idea better. Many thank you’s.

    • February 16, 2019 at 3:04 pm

      I am pretty sure that an electric swatter would set off an instant “stink bomb” so definitely vacuuming is easier on the olfactory system. 🙂

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