An evolutionary war playing out in many of our backyards offers insight into how invasive species behave.
A small parasitic fly, Ormia ochracea, listens to the mating song of the Pacific field cricket to track them down. As these crickets have evolved different songs to escape the fly, it seems the fly has been able to adapt, in a game of cat and mouse.
Robin Tinghitella is a behavioral ecologist at the University of Denver who studies the strange ways these two creatures interact in Hawaiʻi.
"These two started to interact about 35 years ago when the parasitic fly arrived there, and the fly was able somehow to switch to this new host — this Pacific field cricket that it had never encountered before when it arrived in the Hawaiian Islands," she said.
Tinghitella said that there was a period when the Pacific field cricket changed its mating songs, which made it harder for the flies to locate them.
"The crickets were sort of outpacing the flies' ability to evolve — like the crickets were evolving these songs that allowed them to sort of go undetected by flies, but to still communicate with female crickets. So they could attract females, but not simultaneously attract this deadly parasitic fly that was literally going to eat them from the inside out," she said.
She said that when researchers set up song traps for the flies, with new mating sounds, the flies were sometimes able to locate them.
"The overarching message is that the flies' hearing and behavior are pretty darn evolutionarily labile," Tinghitella told HPR. "They have actually evolved to be able to better detect this new host, the Pacific field cricket, and really remarkably to us at least, their hearing and their behavioral responses suggest that they are even evolving the ability to better detect and to locate male crickets that sing these novel songs that evolved just a handful of years ago."
She said that Hawaiʻi, for biologists, is a "magical paradise study system" to observe evolution unfold.
"Almost everything you encounter was ultimately introduced at some point when it floated there, or swam, or flew, or was blown in by the wind, or dropped on the islands by traveling birds or people. So I think this set of characteristics has really led evolutionary biologists to think of the Hawaiian Islands as a sort of unique and ongoing series of evolutionary and ecological experiments," she said.
Tinghitella said that the research has left her with more questions about the interaction between these two invasive species.
"Are we really going to get a co-evolution story here, or are we going to end up with these songs, you know, evolving in a direction that isn't conducive to the fly tracking that? So we're really interested in just getting the opportunity to continue watching this play out in real time," she added.
Click here to view the study led by Tinghitella and Norman Lee of St. Olaf College.
This interview aired on The Conversation on March 11, 2025. The Conversation airs weekdays at 11 a.m.
