Ontario praying mantises are moving further north. What does it mean for insect decline?

Praying Mantis on a New England Aster waiting to ambush its prey - Ontario, Canad Photo by Brian Lasenby/Shutterstock

If you currently live in an urban part of southern Ontario, praying mantises likely aren’t a daily sighting for you. You might have seen one at the zoo, or in a David Attenborough documentary, or maybe the bedroom of a friend with an interest in exotic pets, but likely not out in the wild.

You might not even know that we have praying mantises in Ontario. Though, likely not as many as we used to and not in the same regions.

Anecdotal evidence shows that in recent years, praying mantis populations may be decreasing in southern Ontario and moving farther north to places such as the Greater Sudbury area.

In 2012, Sudburians started to take notice of the new critter taking up residence in their northern town. At the time, staff scientist at Science North, Dan Chaput, told Sudbury.com that this once rare occurrence was likely due to climate change. “Their egg cases are surviving our winters. I attribute this to milder winters,” he said.

This trend—of insects moving north—is not exclusive to the praying mantises. “We are finding that many different species of insect are moving north,” says Heather Kharouba, an associate professor in the University of Ottawa’s department of biology.

“There are lots of factors that could be contributing to insect population decline and migration in Ontario,” she says. “If we are seeing less praying mantises, it is likely due to habitat loss, climate change, and increased use of pesticides as more and more land is turned into farmland.”

So, are there fewer praying mantises in Ontario than there used to be?

Unfortunately, a lack of scientific studies on insect populations in Ontario means that we can’t know for sure whether or not praying mantis populations are declining, but Kharouba tells us that in general, this is the case. “​​Although debate continues among scientists over the magnitude and scope of insect declines, what is unequivocal is that we know enough about insect declines to act now. Declines are occurring and they are rapid,” she says.

In lieu of scientific studies on insect populations, which can be difficult to carry out because of the yearly fluctuations in populations, the lack of historical data compared to more “charismatic” animals or species, and the difficulty in tracking small insects, citizen science becomes a major asset to biologists.

“When regular people are making observations about insects, where they see them, and how frequently, it’s great because it means people are paying attention to the natural world, and it provides us with valuable insights,” says Kharouba.

For example, older generations might remember seeing their windshields covered in a film of dead bugs after an evening drive—something not often seen anymore. Observations like these help inform our understanding of general, long-term trends in insect populations.

If you are interested in doing your part to help track insect populations like those of the praying mantis, you can try out apps like iNaturalist and eButterfly, which allow users to participate in citizen science by documenting the biodiversity they see and sharing their data with scientists.

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