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More praying mantis sightings signal a shift in the Montana bug world

Posted at 9:42 PM, Oct 17, 2021

MISSOULA — The Missoula Butterfly House and Insectarium is one place Montanans turn to when they have bug questions.

This year, the organization tracked a new trend in calls from the community: frequent sightings of the European Praying Mantis.

“The late part of August, and into September and into October, when it's those Western Box Elders, the Woolly Aphids that everyone sees—it kind of looks like it's snowing almost—there's just like thousands of them flying," said Glenn Marangelo, Development Director .

Western Boxelder Bug (Boisea rubrolineata)
Western Boxelder Bugs frequently swam in Montana in the fall and spring seasons.

"And then the other thing that was huge this year were European praying mantises, so big sightings of mantises," Marangelo said.

Like the name suggests, these insects are not native to this region. But the creatures didn’t arrive by accident; they are commonly used as a garden pest control method.

“For probably a couple decades even, they had been annually introduced into places like Montana where they're not native and where winter would kill off any ones that are introduced,” Marangelo explained.

Woolly Aphids (subfamily Eriosomatinae)
Woolly Aphids frequently seen in Montana especially in the fall.

The high volume of sightings this summer suggests to Marangelo and his colleagues a shift.

“We've noticed a big change. So, you know—and we don't have any studies to back this up—but so either number one, there's way more people introducing mantises or number two, our climate has changed enough where they are starting to naturally reproduce," Marangelo said.

According to Marangelo, the sensitive egg casings laid by mantises typically don’t survive Montana’s winters.

“As our winters have become more mild and we get cold spells but they're pretty short, I'm pretty convinced those cases are surviving because they were everywhere this year. I find it hard to believe that it's just from more introduction. I think it's natural reproduction at this point,” Marangelo said.

European Praying Mantis sightings increase in western Montana
According to Missoula Butterfly House and Insectarium Development Director Glenn Marangelo, his organization received several community calls per week reporting sightings of the non-native species.

European Mantises are sizable insects that feed on lots of other creatures, including pollinators.

“My bad equation is it's like putting piranha into Silver Lagoon. I mean, it's a high-end, incredibly effective predator that is definitely gonna have an impact on eating things that are native to our area," Marangelo said.

At this point, the ultimate impacts on the ecosystem at large are unknown. Data sets collected sometimes over decades of time typically allow scientists to illuminate those answers.

And if people call to ask about introducing mantises to their gardens for pest control, Marangelo said his team is discouraging that at this point: “I mean, I love seeing them. They're really incredible animals but I don't think we need to introduce more than there already are into our area.“

The Missoula Butterfly House and Insectarium is set to open its new location at the Missoula County Fairgrounds in 2023.