Female frogs fake death to flee from males

In the wild, love can be a deadly game, and for female European common frogs, survival sometimes means playing dead.

A study published this week in the Royal Society Open Science reveals that some female frogs are resorting to tonic immobility, a freeze response resembling death, to avoid being overwhelmed or killed by overzealous male suitors during the species’ frenzied mating season.

Researchers from the Natural History Museum of Berlin say the finding upends decades of assumptions about amphibian mating dynamics. “It was previously thought that females were unable to choose or defend themselves against this male coercion,” said Dr. Carolin Dittrich, the study’s lead author and an evolutionary ecologist, in an interview with The Guardian. “But females in these dense breeding aggregations are not passive as previously thought.”

During the short but intense breeding window of the European common frog, known as "explosive breeding," dozens of males often pile onto a single female in so-called “mating balls.” These chaotic clutches, driven by reproductive desperation, can result in the female drowning or dying from exhaustion.

In a controlled study involving 54 female frogs, researchers recorded an array of evasive maneuvers. About 83 percent of females attempted to escape the male's grip by rotating their bodies. Nearly half of them emitted high-pitched squeaks, calls similar to those used by male frogs. But it was the final, most dramatic tactic that stunned scientists: 33 percent of the clasped females went stiff, legs and arms outstretched, mimicking the posture of a lifeless frog.

This behavior, tonic immobility, has been documented in amphibians before, but rarely in a mating context. “The most astonishing behavior females exhibited to avoid male attention was tonic immobility,” Dittrich emphasized in her ABC interview.

The researchers observed that smaller females were more likely to employ all three tactics, rotating, calling, and faking death, suggesting a stress-based survival mechanism among younger or more vulnerable individuals. According to the study, these techniques allowed 25 females to successfully escape their would-be mates.

This phenomenon may lie deep in evolutionary biology. Dittrich noted that she stumbled upon an 18th-century text by naturalist August Johann Rösel von Rosenhof describing similar behavior in frogs — a detail that had been all but forgotten for over 250 years.

While the new findings open the door to rethinking the dynamics of frog reproduction, scientists remain cautious. The controlled setup only presented each male with two females, and did not fully replicate the chaotic crowding seen in natural breeding grounds. “In the real world, we often observe the formation of mating balls, but also that females can more easily dive away because there is more structure and places to hide,” Dittrich told The Guardian.

Still, experts say the discovery challenges the long-held belief that females in species with high male competition are powerless.

The findings could also fuel conservation interest, especially as amphibians face sharp population declines globally due to climate change, habitat loss, and pollution. A recent global study cited by ABC News warned that amphibians are the most threatened class of vertebrates, with nearly 41 percent of species at risk of extinction.

Sources:

• The Guardian

• ABC News

• Royal Society Open Science