Play Dead or Drown: How Female Frogs Outsmart Deadly Mating Balls

“She’s just not that into you” isn’t a sentiment that male European common frogs seem to understand—at least not during breeding season. This means their female counterparts have to take more dramatic measures to ward off an unwanted male looking for love. They fake their own deaths.

While pretending to be dead might seem a bit over the top, it works, according to one study published in the journal Royal Society Open Science. Researchers determined that “tonic immobility”—the act of pretending to be dead— is one of several strategies female frogs use to avoid reproductive encounters with males. But do they do it simply because they don’t find the male attractive? No. Their reason for feigning death is much more serious: It is a matter of survival.

Why Do Female Frogs Play Dead?

European common frogs are considered an explosive breeding species, a phenomenon common among amphibians like toads and frogs. When their mating instinct is triggered—usually by a weather event like heavy rain—they simultaneously gather by the thousands at newly-formed temporary ponds.

Once there, the males compete intensely for females to mate with. When explosive breeding is underway, male frogs have the singular goal of finding as many females as possible to mate with. Their quest to mate makes them unusually aggressive. Males will fight with each other in the scramble to find a mate. They will also harass and intimidate female frogs to force them to mate.

In the frenzy of explosive breeding, a female frog can quickly find herself with multiple aggressive males clinging to her. When too many male frogs latch on, it’s a phenomenon called a “mating ball.” However, the term ‘mating ball’ does not reflect how dangerous it is for the female. Mating balls can actually result in the female frog drowning. Playing dead is a self-preservation technique for the female frog. It has nothing to do with how attractive (or unattractive) female frogs find their male suitors.

Playing Dead As a Survival Strategy

To avoid such a fate, the female frog enters a catatonic state that makes her appear dead to the male frog. That involves the female frog lying on her side with her limbs stiffly outstretched from her body, according to Dr. Carolin Dittrich, a behavioral ecologist at the University of Veterinary Medicine, Vienna, and a co-author of the study. But the strategy doesn’t always work. According to Dittrich, sometimes the males will let go, and sometimes they won’t.

Dittrich believes that playing dead is not a conscious decision. It is not a behavior female frogs use to signal disinterest in a mate; rather, it is an involuntary and instinctive reaction to a potentially deadly threat. Dittrich notes that factors like a short breeding season, a high male-to-female ratio, and large numbers of frogs in a small space all contribute to the risk to female frogs.

Is Playing Dead the Only Option?

Faking death isn’t the only way female frogs can avoid unwanted male attention. They have other strategies at their disposal. Their first line of defense is to emit a call that is similar in frequency and structure to the calls made by males. Researchers believe this is an effort to trick males into believing the female is competition rather than a target for mating. If the call is convincing enough, the males look elsewhere and leave the female alone. This allows the female to avoid a physical confrontation that would require a more direct response.

If a male ignores the calls and grabs onto a female, she has a second level of response. Once in the male’s grasp, the female will twist and turn her body to try to escape his hold. This strategy, according to Dittrich, is more effective for smaller females. These three behaviors—mimic calls, twisting, and tonic immobility—are all ways females can avoid or respond to unwanted male mating advances.

Dittrich believes that these avoidance behaviors, especially tonic immobility, evolved out of necessity. Since European common frogs only breed once per season, females do not have the opportunity to develop the physical fitness needed to match male aggression with aggression of their own. They simply lack the physical resources to do so. Instead, the females must rely on avoidance strategies to protect themselves.