This invasive insect from the Mediterranean is now infesting Utah homes

Elm seed bug • Its tiny size makes it difficult to control, pest expert says.

(Photo courtesy Ryan Davis, Utah State University Extension) An adult elm seed bug. These invasive pests appeared in Utah sometime around 2014 and have recently experienced a population boom. The insects have been known to enter homes in large numbers, but are harmless.

A few years after making its first known appearance in Utah, the invasive elm seed bug is showing up in homes across the state.

Complaints about infestations of the pesky, smelly — but largely harmless — bug have increased rapidly during the past year or two, said Ryan Davis, a diagnostician at the Utah Plant Pest Diagnostic Lab. The volume of the reports, Davis said, indicates the invasive insect has established itself throughout the state.

The new pest resembles the boxelder bugs with which many Utahns are already familiar, but the elm seed bug is smaller and its red markings are not quite as bright as the native insect.

Like boxelder bugs, elm seed bugs feed on their namesake trees during the summer and hibernate over the winter in warm cracks and crevices. In some cases, swarms of either insect may enter people’s homes to get away from hot weather.

“Our Siberian elms are like a weed here,” Davis said, “so they’re growing all over the place, especially in urban areas.”

Unlike boxelder bugs, elm seed bugs emit a foul odor, which may make these already unwelcome guests even less desirable, Davis said. They do not, however, bite people or carry diseases.

The elm seed bug made its first known appearance in Utah in 2014, Davis said, though it may have arrived earlier. The bugs are thought to be native to the Mediterranean, but have spread throughout the world, probably by hitching rides on packages shipped internationally, he said.

“They popped up in Idaho in 2009 and Oregon in 2012,” he said. “My guess is they have been around for a while and we’re just starting to notice them as the numbers grow.”

The bugs have been reported in Grand, Tooele, Duchesne and Cache counties, and throughout the Wasatch Front.

The bugs are most likely to swarm inside buildings when temperatures exceed 80 to 85 degrees, Davis said, although the Utah Plant Pest Diagnostic Lab is still working out their preferred temperature range.

The best way to deal with an infestation, Davis said, is to prevent one from occurring by sealing cracks and crevices around a home. Elm seed bugs are specially likely to enter around doors and windows, so ensuring windows and window screens are in good repair is key.

“Keeping them out is tough,” he said. “As someone trying to manage these things, shooting for 100 percent management is probably not realistic.”

Homeowners may consider cleaning up elm seeds and debris, and even removing elm trees entirely, to deal with the pests. Infested homes are usually located near a large elm tree, though the bugs may be able to migrate as far as a block from their food source.

Should the insects get inside, Davis said, the best way to remove them is to vacuum up the pests — being sure to dispose of the bugs immediately. Homeowners could also fill a wet/dry vacuum with an inch of water mixed with dish soap, he said, to drown the bugs and prevent them from escaping a vacuum before disposal.

Spraying certain pesticides that create chemical barriers around doors, windows, foundations and eaves may also help prevent the elm seed bug from entering homes. 

Homeowners who are uncomfortable dealing with the pest themselves may call an exterminator, Davis said. They might also consider contacting the Utah Plant Pest Diagnostic Lab, which can help identify the pests and is looking for more information about their activity in Utah.