Surprise! Exotic leafcutter bee found in downtown Chicago

In the summer of 2018, Andrea Gruver, a master’s student at the Chicago Botanic Garden and Northwestern University, was surveying bees in the Chicago metropolitan area. The section of Metra rail line that runs between the Garden and the downtown Clybourn station is an almost perfect gradient of urban development. So throughout the summer, Gruver and four young interns would climb aboard the train with their hand nets and pan traps to collect bees at eight different sites – areas immediately surrounding eight different train stations – along that stretch of the line.

At the more suburban stops, there were trees and flowers, parks and lawns – the sort of habitat in which you’d expect to find bees. At the more urban stops, the landscape was dominated by concrete and steel, which meant looking for bees in abandoned lots and on flowers growing between cracks in the pavement. However, by the end of the summer, Gruver and her team had collected 83 species and 2300 individual specimens across all the sites.

“We were actually quite surprised with how much we did see,” Gruver says.

One of her most exciting finds was a pair of rusty patched bumble bees in the Rogers Park neighborhood. But she found the biggest surprise of the summer at the Clybourn station: Megachile apicalis, a leafcutter bee not native to North America and never before documented in Illinois. And Gruver didn't just find one specimen; she found 30.

Very little is known about this bee. It’s not clear how it arrived in North America, much less downtown Chicago. Because it’s similar in nesting habits to M. rotundata, the non-native leafcutter that has been intentionally imported for agricultural purposes, it’s thought that apicalis may have hitched a ride in rotundata’s nesting tubes. Apicalis was first recorded in Virginia, questionably in 1883 but certainly in 1931. Since then it's been documented in numerous other states including Ohio, Michigan and Missouri. So it’s possible that apicalis may have crept in from one of those near-by locations. But if it had, you’d think Gruver would have also found apicalis all along the full gradient she was surveying. This bee is closely associated with spotted knapweed, an aggressive, non-native thistle-like plant that Gruver found only at the Clybourn site. She wasn’t sure how the plant made its own way to downtown Chicago, but it might also help explain how apicalis arrived.

Is it possible that these specimens were mistakenly identified? Gruver is highly confident in the identifications. She says apicalis has pretty specific characteristics that set it apart from rotundata, which is the bee it would most likely be confused with. And the identity of one specimen was confirmed by John Ascher through BugGuide.net.

So what should we make of the unexpected appearance of this non-native bee in a place where it’s never been seen before?

“I don’t know if we need to be too concerned now, because it doesn’t seem to be widespread and everywhere,” Gruver says. “But I do think we shouldn’t ignore it.”

Gruver recently published her apicalis findings. Her master’s thesis, “Big City Bees: investigating the effects of urbanization on bee communities in Chicago, IL”, is forthcoming.


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One More Thing…

This is brilliant! Old-school gaming graphics and aesthetics as new-school medium for project presentation. Bonus: scorpions! From Elisa~ @Minakokiss via Twitter.