To prevent the typical chaos that arises during mating, certain female frogs adopt a unique strategy. A study released on October 11 in the Royal Society Open Science journal reveals that female European common frogs sometimes feign death to keep eager suitors at bay.
Researchers from Berlin’s Natural History Museum set up an experiment involving one male frog, one larger female, and one smaller female frog in a container.
They documented the mating interactions and noted that out of 54 occasions when females were seized by males, 83% of them tried to twist their bodies to break free. Nearly half of the seized females produced sounds, like squeals and grunts, and every one of these vocalizing frogs also twisted their bodies.
In 33% of the encounters, the female frogs displayed tonic immobility, a behavior where they extend and stiffen their limbs to mimic being dead. This particular behavior often coincided with the twisting and vocalizations. The smaller females were more prone to employ a combination of all three defenses compared to the larger ones.
Fascinatingly, this behavior isn’t entirely new. Study co-author Carolin Dittrich shared with The Guardian an old book from 1758 by Rösel von Rosenhoff that detailed this exact behavior, but it was never discussed again.
“There was an earlier belief that females couldn’t resist or defend against male advances. However, females in such crowded breeding groups aren’t as submissive as once believed,” Dittrich explained.
The researchers suggest that this could also be a test for the male’s resilience and vigor, traits that might increase their offspring’s survival rates. They also highlighted the need for a broader sample size to ascertain whether the smaller females are more adept at evading.
This tactic isn’t exclusive to frogs. The term “playing possum” alludes to a survival strategy employed by the North American opossum found in the US and Canada. When threatened, this marsupial will flip onto its back, revealing its fangs, salivate excessively, and emit an off-putting scent from its anal glands as a deterrent.
In 1975, an experiment found that both North American wood ducks and vibrant mallard ducks would feign death when faced with predators. Remarkably, the ducks would remain immobile even when taken to the predator’s lair, choosing to flee only later. Experienced foxes soon learned to swiftly incapacitate these seemingly deceased ducks.
Intriguingly, certain sharks and rays, despite being apex predators, also manifest tonic immobility. Confronted with danger, lemon sharks will roll onto their backs, exhibit erratic breathing, and sporadically tremble. Zebra sharks have been known to maintain this state even during transportation.
Male spiders involved in “nuptial gift-giving” have a distinctive type of death-feigning behavior known as thanatosis. This ritual is part of their courtship, especially when dealing with potential female cannibals.
In a study from 2006, when an interested female approached, the males would pretend to be dead. Upon feigning death, the males remained still, clutching a prey gift they had ensnared and encased in silk. The male would only gingerly move when the female consumed the gift and started mating.