UTM student discovers parasitic fly preying on crickets in lethal, Aliens-style evolutionary fight

A new study out of U of T Mississauga reveals a dramatic, gruesome and deadly battle for survival quietly playing out on the campus fields.

Erik Etzler, who recently graduated with a master’s in ecology and evolutionary biology, has found that the common campus tree cricket, perhaps best known for its soft, buzzing musical notes during the long, warm summer evenings, is an unwilling host to a lethal parasitic fly that preys on the young. 

A native fly known as Stylogaster neglecta, which is part of the parasitoid family Conopidae, are roughly the size of a mosquito, with a similar body shape, Etzler says. Researchers knew the fly was parasitic, but it was Etzler who recently uncovered which insect the fly uses as a host.  

Using a tube-like organ, the fly stabs a nymphal cricket, embedding eggs into what Etzler describes as teenage crickets in their third or fourth molt. He says the young crickets “look fine” after the eggs have been embedded into them.

But inside is a larva that, over time, feeds on the viscera of the immature cricket. Then, like a gruesome scene from a science fiction film, a fly maggot emerges from the abdomen of the cricket, killing its host in the process.

And it’s not just a few crickets that find themselves an unwilling carrier to a parasitic fly. Etzler found 40 per cent of the crickets he netted at UTM’s old field had eggs embedded in them, meaning there is a 40 per cent mortality rate among the campus’s young cricket population.

Curious if the phenomenon was localized, Etzler expanded his study to include three other sites. He netted crickets at sites in Cambridge, Ont., King City, Ont., and Albany, NY. He found young crickets carrying the fly larva at each of those sites as well.

Only one cricket, he says, made it to adulthood before dying. He suspects it’s because it was “stabbed late.”

Etzler’s study, published in The Canadian Entomologist, is the first to reveal that this fly parasitizes tree crickets.

Etzler says that he finds it bizarre how little was known about this fly. It was first described in 1890, he notes, yet no one learned much about it for 100 years.

“It’s shocking how poorly we understand it,” says Etzler, who stumbled across the fly while cleaning up the lab.

He explains he found dozens of flies that had come out of crickets collected by previous graduate students. The flies were identified and left in a box.

Almost 20 years later, Etzler, who had been looking for a master’s project, decided to tackle the packed-away mystery.

His research has shed new light on an environment where “bizarre things” happen.

“It’s a dramatic world out there,” he says.