Elm Seed BugThey’re baaaack…by the thousands, and they are driving people to distraction. The Elm Seed Bug (ESB) Arocatus melanocephalus, discovered last year in Idaho, has started showing up again this year and is a significant nuisance to homeowners. This insect is new to the United States and was, unfortunately, discovered right here in SW Idaho. Ada, Canyon, Elmore, Gem Owyhee, Payette and Washington counties had infestations in 2012, as did Malheur County in Oregon. The Department of Agriculture isn’t sure how the ESB came into Southwest Idaho but they do know it is commonly found in south Central Europe where they have also been found on Oak and Linden trees.

The ESB is related to Box Elder bugs and belong to the order Hemiptera. There is usually an X pattern on the back of insects in this order where their wing covers cross over their backs. The ESB is about 1/3 inch long and is brown in color. An identifying feature is the black triangular shield on its back. The flip side of the insect has reddish markings. They have a tube-like mouth part known as a proboscis, so there is no biting.

The ESB overwinters as an adult, emerging in the spring to mate and begin the cycle again. Luckily, the insect does no damage to people, trees or buildings, they just show up in such numbers that they make us crazy. This time of year the insect wants to escape the heat by trying to get indoors. Later, they’ll try to escape the cold by trying to get inside to overwinter.

According to the Idaho Department of Agriculture, the best way to manage this pest is by exclusion. They state treating with pesticides offers little relief at this time. While pesticides will kill the insects that have direct contact with the product, it won’t prevent the next wave of insects from trying to enter your home. They suggest pest proofing your home if possible. An added benefit is that most of these ideas are also energy conserving. Some ideas include;

• Installing door sweeps on all entry door. Pay attention to bottom corners.

• Don’t forget the garage doors.

• Seal beneath sliding glass doors using a foam weather stripping

• Caulk cracks around windows.

• Repair gaps and tears in your window and door screens.

• Seal openings around pipes, cables and vents where they enter the house. Steel wool, caulking or expandable foam are all materials that can be used for that purpose.

After all that if they still get inside, use a vacuum so capture them then throw the bag away so they don’t crawl back out. Don’t crush them as they produce a nasty odor.

Some folks want the elm trees in their neighborhood cut down but that won’t solve the problem. Possibly in years to come there will be a natural predator to help with the control of this insect but for now, take a deep breath and grab your vacuum.

Another good article with pictures can be found on the Idaho Department of Agriculture website. Click here.


  1. angela says:

    I am BOMBARED with these darn things…. its so bad that my ground moves and walking through them, they are flying into you and landing on you, etc. Is there a ground spray insecticide that will kill them off?

    • Rachel Lacow says:

      Angela, you think you have it bad? These guys have decided that they like sleeping in my bed with me at night !! (GROSS) I am constantly killing them in my room (mostly in and around my bed)!!

  2. Elm seed bug killer says:

    They recently have been coming into our house (I’ve only seen about 4 in-in the house) other than that they usually just hang around our screen door and on the glass door and I’m always killing them. Nasty little things. At first I thought that they were cockroaches but a few moments ago one flew onto my computer screen and I freaked. I decided to look them up more in depth than just cockroaches and thanks to this article I now know I’m screwed since there’s no insect spray to actually kill them for good, but I will caulk the crap out of my house.

  3. Rochelle says:

    Praying Mantises will eat them! They have worked GREAT at my house! Purchase praying mantis eggs in the spring and place them around your house, front and back.

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