Insects Can Fake Death for an Hour to Evade Predators

It makes them less appealing as a potential meal.

European antlion (Euroleon nostras) on its dorsal side playing dead
European antlion on its back playing dead.

Nigel R. Franks

Possums aren’t the only animals that, well, play possum.

A new study finds that animals feign death for long periods of time in order to escape capture from their predators. How long they are motionless depends on the circumstances but they can wait out their predators quite a long time when their lives are at stake.

“Surprisingly, I think it is not only common but extraordinarily widespread in the animal kingdom. 

Woodlice do it, as do beetles, slow worms (a kind of legless lizard), chickens, rabbits and, of course, possums,” lead author Nigel R. Franks from the University of Bristol's School of Biological Sciences, tells Treehugger.

In science terms, researchers call this process “post-contact immobility” because saying an animal is playing dead implies that the predator has some notion whether the potential prey is alive or dead, Franks says. He and his team were curious why animals act this way and how long they do it.

Their results were published in the journal Biology Letters.

Studying Antlions

Animals stay still to avoid capture for varying lengths of time.

“Most intriguingly Charles Darwin recorded a beetle that remained motionless for 23 minutes. Antlions, our favourite study creature in this regard, gave us a record of 61 minutes,” Franks says.

Antlions — also known as doodlebugs — are members of a large group of insects. Antlion larvae dig pits in loose soil and then aggressively attack ants and other small insects that tumble down into the sandy pits.

For another study, researchers were excavating sand pits to understand the physics of how antlion larvae build their pits. As part of their research they needed to weigh the individual larvae. When they tipped them into the microbalance scale to weigh them, they noticed that the larvae remained stationary for long periods of time.

“This made it ‘a piece of cake’ to weigh them but it prompted the question ‘What on earth were they playing at?’” Franks says. “We simply had to investigate and the paper we published is one of the results of our investigations.”

The researchers found that the amount of time the antlions remained motionless after being disturbed was unpredictable and was often quite lengthy. In researching other animals, they found that how long they wait to move again can depend on factors such as hunger and temperature. But it always varies.

This unpredictability is absolutely crucial for their survival, Franks says.

For example, if a bird visits these antlion pits and the larvae “play dead,” the birds will hover around the antlions to see if they stir.

“Imagine that antlions always remained immobile for 5 minutes. In such a case, the predator could look for alternate prey and then return to its original one when the time is up,” he says. “Indeed, the time would be up for such a predictable death-feigner.”

But because the time is unpredictable, the birds leave and go find something else to eat. The predators turn their attention from the unmoving prey that no longer catches their eye to something nearby that is a better (moving) alternative.

As the researchers write in the study, “Indeed, the best place to hide a needle might not be in a haystack but in a large pile of identical needles.”

View Article Sources
  1. Franks, Nigel R., et al. "Hide-and-Seek Strategies and Post-Contact Immobility." Biology Letters, vol. 17, no. 3, 2021, p. 20200892, doi:10.1098/rsbl.2020.0892