Gardening & Living in Grand Style
Elm seed bug — another new insect friend or not?
by Michael Johnson
Utah State University Extension Agent, Grand County
Sep 08, 2016 | 3980 views | 0 0 comments | 132 132 recommendations | email to a friend | print
Elm seed bugs are showing up in large numbers as summer draws to a close.   
Photo by Michael Johnson
Elm seed bugs are showing up in large numbers as summer draws to a close. Photo by Michael Johnson
I must admit that my years with USU Extension have made me somewhat immune to the perhaps more average concern over insects. Once you have seen so many and heard the stories over so many years, most insects just cause a shrug, although I admit a few in particular do “bug” me.

The squash bug is one of those and it’s because of my love of squash and the difficulty in getting long-term production when squash bugs show up in the garden. Mosquitos are another, because I prefer to be in charge of my own blood draws. However, I digress.

I mention the lack of insect concerns because over the last month the building where my office is housed has been inundated with little flying insects. Early on I determined they were in the Hemiptera order, which includes the boxelder bug, stink bug and others, but I wasn’t sure exactly what they were. Now, if you worked in this building you would know this isn’t the first insect invasion we have had over the years in and around our office. We’ve seen at times hordes of pill bugs, millipedes, tent caterpillars, miller moths, tamarisk beetles, grasshoppers and more, all at least partially due to the wooded area behind the buildings.

So this little insect has been flying around in the hallways and rooms, crawling on the walls and doors, but not causing any issues I could see other than being a nuisance. Curiosity finally won out and led me to discovering it was the elm seed bug, which is a different insect from the elm leaf beetle.

According to the Idaho State Department of Agriculture, the elm seed bug, Arocatus melanocephalus, of the Hemiptera order and Lygaeidae family, was first detected in the United States in 2012 in two counties in Idaho. Apparently, it’s been making its way through Utah ever since. As you would expect from the name, this insect primarily feeds on the seeds of elm trees, which our Siberian elms generously share with us, and like the elm leaf beetle, it doesn’t pose a threat to people or buildings, but loves, apparently, to be indoors and bring its extended family.

These insects overwinter as adults and then in the spring mate and lay eggs on elm trees, with the larvae feeding on the elm seeds. Again, we know there’s plenty of their food in our area. They are about one-quarter- to one-third-inch long, dark in color, with a reddish-colored abdomen on the underside. And as with many Hemiptera, their crossed wings create an “X” pattern on their backs. There’s also a triangular black shield-like plate on their backs, called the scutellum, which is sided with a reddish color. When I initially looked at them in my office, while I could see the X, the back of the insect just looked dark, almost black even, when I looked with a hand lens. Then, when I looked at them outside in the natural light the reddish markings on the back showed up quite clearly.

So what do you do if this insect decides your home is a great place to spend the heat of a summer day, which they like to do? Luckily, summer is winding down. However, don’t breathe a sigh of relief yet, since it’s said they also like to spend the cold of winter inside. First, try to learn patience — believe me that is important. Next, as with all inside-loving insects, make your house as tight as possible — and I mean tight, since this insect is small. Cover, caulk or otherwise fill up any outside cracks, and install weather stripping, repair screens and make sure they fit tight. Beyond that, I suggest you consider buying a really good hand vacuum to vacuum them up, but don’t just go outside and dump them out since many will just find their way back in.

A more permanent solution would be to dump them in a bucket of soapy water. What about using pesticides around the outside of the house, you ask? Well, considering the amount of elm trees in our area and the incredible amount of seeds, I don’t see that being a useful process as there will always be more of these insects. It’s much better to spend your time pest-proofing your home. Lastly, I have seen them congregating on the outside of buildings, and if so, a strong stream of water or a soapy spray should knock down their numbers. Hopefully, they will at least eat a lot of elm seeds!

Thought for the day: “Don’t take things too seriously, and just chill.” —Kailash Kher.

Previous articles are available at The Times-Independent website, Have an idea you’d like Mike to consider writing about? Want more information about these topics? Call the Utah State University Extension Grand County office at 435-259-7558 or email Mike Johnson at

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