The act of pretending to be dead is scientifically known as thanatosis or tonic immobility. While it’s a known anti-predator strategy across various animal species, its application in avoiding mating is a more recently studied aspect in some amphibians.

How it Works
The “Playing Dead” Mechanism:
When a female frog engages in thanatosis to avoid mating, several behaviors have been observed:

  • Limp Body: The female will go completely limp, relaxing her muscles, which makes it difficult for the male to maintain his grip during amplexus (the mating embrace where the male clasps the female).
  • Limb Extension: She might extend her limbs rigidly or splay them out, further hindering the male’s ability to hold onto her effectively.

  •  Body Rotation/Flipping: Some females have been observed to rotate their bodies or even flip upside down, making it an awkward and often unsustainable position for the male to continue amplexus.
  • Submersion: In aquatic environments, the female might even submerge herself partially or fully, playing dead at the bottom, which can cause the male to release her as he may perceive her as deceased or simply lose his grip in the process.
  • Lack of Response: Crucially, she will cease active movement and vocalization, appearing unresponsive to the male’s advances.

Why They Do It:

Avoiding Unwanted Mating
This behavior isn’t random; it serves specific purposes for the female:

  • Mate Choice: Female frogs often have preferences regarding their mates (e.g., size, vocalizations, genetic compatibility). Playing dead allows them to reject males they deem unsuitable.
  •  Avoiding Harassment: In many frog species, males vastly outnumber females during breeding season, leading to intense competition and sometimes aggressive mating attempts where multiple males might try to clasp a single female. Thanatosis helps females escape such overwhelming attention.
  • Energy Conservation: Successful amplexus can be energetically costly for females, especially if they are already carrying eggs. Avoiding unwanted or unsuccessful mating attempts conserves valuable energy.
  • Reducing Predation Risk: Prolonged amplexus can also make both the male and female more vulnerable to predators. By ending an unwanted encounter, the female reduces her exposure time.

Research and Species Observation

This behavior has been particularly well-documented in the common frog (Rana temporaria), a widespread European species.

Researchers have conducted studies observing this behavior in breeding aggregations, noting how females employ this strategy to escape unwanted amplexus, especially from smaller or more persistent males. It highlights a female’s active role in mate choice, even in species where males appear to dominate the mating process.

This intricate behavior demonstrates the complex strategies animals employ to navigate the challenges of reproduction and ensure their survival and the success of their lineage.