Elm Seed Bug

Many residents of the US are familiar with the box elder bug, an orange and black bug found on box elder trees in summer and found in homes in the late fall and winter as it looks for a sheltered place to spend the winter. True bugs that invade homes in summer in large numbers are uncommon. US residents may become familiar with a new species of red and black bug, the Elm Seed Bug, Arocatus melanocephalus.

The Elm Seed Bug was not considered a pest anywhere until 1999, when residents of Northern Italy complained about home invasions by large numbers of these bugs. The largest outbreaks of home invasions occurred in late May in the years 2001-2003. Every year since, invasions have been reported in different locations in Italy. Some evidence suggests that the home invasions are correlated to spells of unusually hot weather.*

Arocatus melanocephalus, the Elm Seed Bug

Like many Seed Bugs, the Elm Seed Bugs overwinter as adults, mate in spring and lay eggs on elm trees. The larvae feed on the fruits and seeds in May-June in Italy, and become adults in summer. Like most true bugs, the Elm Seed Bug has scent glands that produce a noxious odor, that deters predators. When crushed, the bugs produce an unpleasant odor.

Insects that invade homes in large numbers are prime candidates for global transport by hitchhiking in the baggage of travelers. Recently, the Elm Seed Bug has appeared in Southwestern Idaho. The bug is not expected to cause damage to Elms or have large ecological impact. Whether or not it becomes a nuisance or spreads around the US remains to be seen. The USDA/APHIS is asking the public in Idaho to be on the look out for this pest to help determine the extent of its spread.

Elm Seed Bugs Aggregate Indoors
Photo: mauriziano

*Maistrello, et al. 2006. Journal of Thermal Biology. Volume 31, Issue 8, Pages 594–598.

About jjneal

Jonathan Neal is an Associate Professor of Entomology at Purdue University and author of the textbook, Living With Insects (2010). This blog is a forum to communicate about the intersection of insects with people and policy. This is a personal blog. The opinions and materials posted here are those of the author and are in no way connected with those of my employer.
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21 Responses to Elm Seed Bug

  1. Anonymous says:

    I live in Pacifica Ca. and have observed these bugs on my property in the past 3 – 4 years. I have not seen any this year. We only see a few at a time , less than 10, Ours are black and orange, we call them SF Giants bugs

  2. jjneal says:

    There are a lot of look alikes. You may be seeing large milkweed bugs or boxelder bugs that look similar.

  3. bob says:

    I have a large elm next to my house and have had a problem with these bugs for eight or nine years now. They get into the house in large numbers and are a real nuisance, but mostly on the side next to the elm tree. Can you tell me how to distinguish them from the boxelder bug? They are definitely not Milkweed bugs. My house is on the Russian River in western Sonoma County, CA. If these are indeed Elm Seed bugs, is there someone I should contact?

  4. Anonymous says:

    I live in Boise, Idaho and my house has been swarmed by this bug. I do not have Elms on my property but my neighbor does. If we spray the trees in the Spring will this help to control the numbers. I have been fighting the infestation for 3 weeks now and am about ready to move. I have sprayed the exterior three times which has helped keep the masses at bay, but they are still coming into my house-I guess through the window glides-even though I have sealed them as well as I can. Any other advice? Thanks

    • jjneal says:

      It is a new problem, so solutions are being tested. The vacuum cleaner is your friend.
      Bugs can crawl back out the hose so empty the bag or keep it closed so they cannot escape.
      An effective trap would be helpful.

  5. Vicki says:

    I also live in Boise and even in January, I find these bugs every day on my windows and flying around the house. I have bought a small shop vac just for the purpose of vacuuming up these pests- I put a small amount of soapy water in the bottom of the shop vac so they will drown! They leave their marks on the windows and the house siding. Why are they active even in winter? We have had a spell of very cold weather (-5 º F) and it did not seem to stop them at all. How are they staying alive in the winter since they feed on elm seeds?
    What is an effective trap?

    • jjneal says:

      Good idea with the shop vac. Their metabolism slows in the winter and they can go long times without eating.

      For some brown marmorated stink bugs, people cut the top off a 2 liter soda bottle and invert it to make a funnel into the bottle. Duct tape the top to the bottom. A cheap batter led light attracts stink bugs in the dark, like a closet or attic. I don’t know if it will work on these elm bugs.

      Soapy water in the bottom of the shop vac is a good idea.

  6. Vicki says:

    Thanks for your reply and the idea of the soda bottle funnel! I will try it.

  7. Anonymous says:

    I live in boise also and im having these bugs all over my residence

  8. M.E. Cole says:

    I am in Boise Id also and with this 110 degree heat the Elm Seed bug is working overtime! This may sound odd, but I have an older home that has an 2-4 inch area between the screens and window. I sprinkle the area with salt. This stops the majority from making their way in…although I don’t know the reasoning as to why. It also stops the ants from coming in. Obviously the smarter bugs simply walk up the wall and around the salt, but they are few and far between, not the huge numbers as before. One could try a window ledge if they have one. My bathroom used to get the most and this has stopped them completely! I am going to try to wipe down an area that I don’t care about it getting ruined with heavy salt water to see if that will stop them from coming in at an area where there is no ledge to put the salt.

    • jjneal says:

      Hopefully the salt doesn’t rust or corrode your screens. The screens without the salt may be effective. Ants often forage indoors early in the season but then stay outdoors when more food is available. People over estimate the effectiveness of ant treatments as a result.

      In the Midwest triple digit weather last year, insect activity was depressed in the really hot weather. The bugs like air conditioning, too!

  9. I live in Boise, too. The hotter the weather — the more of these bugs I find in my house! I thought this year they had moved on — didn’t see any of them. Alas, we hit triple digits, and they are trying so hard to get into the house — what is gross is that they will hide behind picture frames and under items on the floor (my sons’ remote control car, for ex.) — they mass there. Yuck. We have put dimataceous (sp?) earth at the corners of the doors and in the window tracks — the old house windows are an easy way in. Hate them! Any other advice for getting rid of them is much appreciated!

  10. Sarah says:

    I have them at my house in Boise, Id too- Never had a problem until today. I am pretty sure I accidentally let them in yesterday when I went outside to water plants and had not completely closed my screen door. This evening I have killed about 50 of them, and they keep showing back up in groups of 3-8 of them, crawling around the ceiling near my ceiling fan. Makes me feel like they are hiding in the hardware and coming out when I remove/flush their friends. Quite gross. Disappointed that until yesterday I never had a problem with these pests, but then again- it’s been over a 100 degrees for five days and they are trying to escape the heat! The article I have included below also recommends the shop vacuum with soapy water. We are two years new with these invasive species from what I read (Elm Seed Bugs new to the US, found in Idaho during the summer of 2012), so I think there may be a learning curve in removing them otherwise. Best of luck and please share any secrets you have! Too bad a fly strip or other attracting mechanism isn’t available to gather them! http://www.kivitv.com/news/local/198825511.html

  11. David Williams says:

    I live in Nampa, Idaho surrounded by Elm trees. I have these bugs in mass quantities. Been using the shop vac, my friendly spider bros who hang out in corners, and used a can of old insecticide I had from a couple of years ago..it dropped them very nicely. I thought it was Raid Ant and Spider..had a brown plastic lid. I am kicking myself for tossing the empty can, because the next can of Raid Ant and Roach I bought did nothing and I am unable to find what I thought I had used last. They are attracted to light so I have white LED night lights near the spiderwebs and they seem to be going there and becoming spider food. I will try the pop bottle trap too.

  12. bob says:

    i live in Boise with an elm three in the back yard. these bugs are every where .i found that a mild dishsoap and water solution stops them in their tracks but i have to keep doing it every day they keep coming!i like the vacuum idea and i wil try the diametrious eath thing too.

  13. Jim says:

    I am also a Boise resident with the Elm bug problem. It is now late February 2014 and I’m already finding a few bugs around the house. Our house is old with aluminum siding covering original wood siding and a few old windows. It is really hard to seal an old house per instructions. And they seem to get through new vinyl screened windows too. They also have gotten into attic vents that I don’t want to block or seal. It would be helpful to post a summary of what works. Does spraying bugs outside on your house with soapy water kill them? Do you know if birds are attracted to them? I would not use a bug killer spray if it results in killing birds that eat poisoned bugs.

  14. jjneal says:

    They will get hungry and leave in the spring. You might contact Idaho extension to see what they currently recommend for control. Brown Marmorated Stink bugs can be captured in light traps. Cut the top off a 2 liter soda bottle. Attach a battery operated LED light to the inside of the bottom. Fit the top as a funnel leading into the bottom. Duct tape it together. Placed in a dark attic or a dark room it attracts Brown Marmorated stink bugs. It may work for elm seed bugs but I have no reports. It may be worth a try.

    • I live in Boise and I am going to try this! Thanks for the tip.

    • Marie Cole says:

      Boise resident here and Idaho Extension didn’t have any ideas either since any insecticide used had to be directly applied to bug and even then many were useless. So, this brings me to your trap. I think I missed something. What prevents them from just crawling back out? And the Elm Seed Bugs I encounter mostly seem to come in at night when it is dark. They especially like my bathroom widow so I thought it was due to the humidity level. I don’t have the same issues around any of the other windows or doors I have here. I don’t have the attic invasion like some do. Last year I stopped a majority of the bugs from getting past the window seal by using sea salt and water mix sprayed daily on the inside and outside of the frame as well as sprinkling some salt in the corners I thought they might be getting through. Someone was concerned about the damage this would do to the wood (which is what I have since it is an old house) and it didn’t hurt it. I suppose those with metal or aluminum would have to reconsider this method. At least I wasn’t finding the bugs hidden in my shower curtains, or falling from my towels when I moved them or dropping on my head when I walked in in the mornings! One more interesting note is I have a window/screen in my bedroom door that does not have a tight seal at all and rarely do I find an Elm Seed Bug here, so again I am wondering if it isn’t a moisture issue? On the contrary I do know they do not like direct water since they attempt to “fly” away from any wet spray and huddle in when attempting to wash them down the drain. There has to be some sort of level they are seeking. Anyway…just my two cents.
      Good luck everyone!

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