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Ubiquitous insect likely to bug Garfield County homeowners into the future

The elm seed bug adult is about 1/3 inch long.
Colorado State University Extension

There’s a new bug in town.

It’s small and brown and smells like bitter almonds, especially when crushed.

To make things worse, hundreds of them can get inside your house and crawl around.

The elm seed bug is considered a nuisance pest by Colorado State University Extension, meaning it doesn’t damage homes or people and does minimal harm to elm trees, according to an Extension fact sheet.

“These are about 1/3 inch long with dark, rusty-red and black coloration,” the fact sheet states. “The underside of the insect is red. On the back behind the head, there is an upside-down black triangle set inside two rusty-red triangles.

“Next to the edges of the wings are noticeable white dots interspersed with rusty-red and black dots. Wings are held crossed over the back and half of the wing is black and the other half is red and black.”

Native to Europe and the Mediterranean, the elm seed bug prefers to feed on Siberian elms, but is not picky about meals in general. They first appeared in the United States in 2012 in Idaho.

“This insect feeds primarily on elm seeds, but has also been reported on linden and oak trees in Utah,” CSU Extension’s fact sheet reports. “Elm seed bug adults become a major nuisance pest, similar to the boxelder bug, by entering homes and buildings in great numbers.”

They’re also fairly harmless — It’s just annoying to see and smell them. Or feel them.

“I wake up with them crawling on me,” said Jill Patrick of Glenwood Springs, who said the elm seed bug is “way worse” than any other insect problem she’s had to deal with.

They’re not even good houseguests.

“They poop on the walls. They have no manners,” said Meredith Shrader, CSU Extension entomologist.

Shrader, who works in the Grand Junction area, said some people have thousands of the bugs in their homes.

The bug was first reported in Colorado in July 2017 and established itself in Mesa, Delta and Montrose counties to the south of Garfield County, according to the fact sheet.

“They’re on a parade across the state,” Shrader said.

It’s now traveled up as far as Basalt, said Chris Harvey, manager at Mountain Pest Control.

“They’ve been in the [Garfield County] area for about two to three years. … We’ve seen them on the [Highway] 82 corridor up to about Basalt, Missouri Heights, but from there up we haven’t seen much activity,” Harvey said.

It is unknown how the bug got here from its home in Europe.

“To my knowledge nobody has been able to find the introductory source,” Shrader said.

And even if their predators in their native habitat were known, it is a 10-year process to introduce a predatory insect into the U.S., Shrader said.

Locally there are birds, lizards, spiders and praying mantids that may feed on the elm seed bugs, but the sheer number of pests may be too much for local predators to handle.

“Everybody gets full at the buffet eventually,” Shrader said. 

They’re smaller than another local nuisance pest, the box elder bug, and can slip through cracks in window frames.

“They’re such a thin, narrow type of insect that it doesn’t take much of a crack or crevice for them to end up inside,” Harvey said. “A lot of the windows these days have weep holes for moisture to escape, and the elm seed bugs will come in right through those weep holes. … Sometimes we go out to homes and open the door and the inside of the door jam is just inundated with those elm seed bugs,” Harvey said.

Completely ridding your home of the bugs is probably not realistic. 

“A little bit of treatment here and there can help keep the numbers down, but it’s not a cure-all by any means,” Harvey said.

Shrader agreed. 

“Spraying the exterior of your house is minimally effective. It might keep half of the insects from coming in,” she said.

Patrick took that step further, saying that spraying helped “not a lick.”

Harvey said treatment focuses on areas of ingress. In addition to applying pesticides it’s important to seal around windows and doors, Harvey said.

“$5 worth of caulking helps out a lot,” Shrader said.

Spraying or cutting down elm trees is an ineffective way to control the bugs, Harvey said.

“I’ve had people go to the extreme of eliminating all their elm trees, which I don’t promote whatsoever. … But they can come from other people’s lots and homes that have elm trees. It’s not like if you don’t have an elm tree you’re never going to see an elm seed bug,” Harvey said. 

A complication in that regard is the bugs feed on oak and linden trees as well as elms.

“Just because we find them on certain trees doesn’t mean they won’t inevitably find something else to eat if you remove everything that they prefer,” Shrader said.

Garfield County vegetation manager Steve Anthony had a different experience. After suffering through two years of elm seed bug infestation, he cut down an elm in his yard and saw a marked reduction in the bugs. But this tree was the only elm nearby his Castle Valley neighborhood.

“We cut it down this spring — it was just a solitary Siberian elm — and we’ve had just a handful of those elm seed bugs after we cut that tree down. So I think if you do have an individual tree that’s kind of isolated and there aren’t others around, from my experience, it works,” Anthony said.

If the bugs find their way inside, the Extension fact sheet’s first step in managing them is to vacuum them up.

“I vacuum them up, and I deal with the nasty stink,” Patrick said.

While the bug has been in the area for a number of years, it seems to be more prevalent this summer.

“We do tend to see more of them during the hot, dry periods because they’re trying to escape it like everybody else,” Shrader said.

The bugs appear in late June and persist into the fall, the fact sheet says. But the cooler fall weather will not spell the end for the insects. They will just move to the south side of buildings to find warmth, Harvey said. 

The bugs overwinter as adults, so they can even be active during the winter on warm days.

“There’s a [misconception] that when it gets supercold all insects die off, but that’s not the case. If that were were the case we’d start the next spring with no insects,” Harvey said.

There is some hope that with time and observation more effective treatments will be developed.

“We’re still learning about the pest. We’ve just been dealing with it since 2017,” Shrader said.

But for now we’re stuck with them.

“There is absolutely no sign that they are going away,” Harvey said. “It’s something that we’ve got to learn to live with.”  

cwertheim@postindependent.com


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