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The power of the game of the dead

Antlion larvae are notoriously ferocious: they dig pits in the sand to catch unsuspecting prey, stab it with their sharp jaws and grind it from the inside out.

But everything is relative. For their own predators, ant larvae are just small snacks. And the cunning traps of the colony, grouped together and quite visible in the sand, are like flashing DRIVE-TROW signs.

Instead of gathering active protection, the larvae are armed with passivity – they respond to the provocation by lying completely motionless, for unpredictable time intervals, which can vary from seconds to more than an hour.

In an article published this week in Biology Letters, researchers model how this behavior can give antlions a leg up against impatient predators – and in the process shed new light on the game of dead, widespread behavior, the effectiveness of which is mysterious to researchers.

Nigel R. Franks and Anna Sendova-Franks, married biologists at the University of Bristol in England, have been studying insects for more than 30 years. In 2016, during an unrelated investigation of antillion larvae, they decided to weigh some of them. “I thought it was going to be a nightmare of impatient bugs,” Dr. Franks said. Instead, when they lean on the scales, the larvae freeze quickly.

The researchers pulled out their chronometers. Under their gaze, a larva remained motionless for 61 minutes. “Watching dry paint would be fun to compare,” said Dr. Franks. “But it was so amazing.”

Many animals behave in a similar way when faced with danger. Larger vertebrates, such as possums, can emit bad odors to reinforce the illusion that they are dead and therefore not tasty.

But for some creatures like antillion larvae – eaten by animals, like birds that are set in motion – the key may not be false rot, but immobility, said Dr. Franks, who therefore prefers the term “immobilization after contact.” “Maybe they are not playing dead, but hiding in a prominent place.

On their next research trip, the researchers determined the time during which all ants in the population played dead, and found that this was extremely variable.,, even when the same larva has been tested twice.

Such inconsistency can be part of a survival strategy. If the stay of an antillion larva was predictable, predators “might be able to learn some patterns,” said Dr. Sendova-Franks. But if there’s no model – and there’s more food nearby – a predator can just move on, like someone with a bag full of Lays who accidentally drops a chip on the couch.

To test this idea, the two biologists and their colleague Alan Worley simulated a hypothetical community of ants endangered by a bird. In their scenario – based on the limit value theorem often used in ecology to model the behavior of feed the bird visits a spot of anion holes and bites the larvae outside, but sometimes drops them.

If a simulated larva is dropped, it remains stationary for a different time, informed by the real observations of the researchers. The bird waits for a spell, and if the antlion does not move, it abandons the mistake to look for a dish that is still moving.

After conducting the simulation thousands of times, the researchers found that “playing the possum” really helped the antillions: This increased the survival rate of a patch by about 20 percent.

And while reducing the lengths of the larva’s immobility spells in the model significantly reduced the survival rate, increasing them was unlikely to have an effect – assuming the ants took their strategy to “absolute extremes,” Dr. Franks said. “Which is sweet, I think.”

This model will allow researchers to compare the benefits of the possum game between different species and populations, helping scientists understand the effectiveness of behavior and how it has evolved, said Kenan Oyen, a postdoctoral fellow at the University of Cincinnati who is not involved. work.

The next step is to “confirm on the spot some key assumptions of the model,” including that immobility actually helps prevent predator ants, said Alejandro G. Fargi-Brenner, a professor of ecology at the National University of Comaue in Argentina.

Antlions remain formidable opponents of everyone around them in the food chain.

“Playing dead is such a great way to waste predator time,” Dr. Franks said. That changes the game.

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