August: faked death | News and features

Many animals remain motionless after contact with a predator as a last defense measure.

This behavior is so common that it can be found in sentences like “play dead”. Under extreme circumstances, this is even said to happen to humans.

In previous studies conducted by the same team with antlion larvae, scientists found that they became motionless when handled individually.

At some point the larvae need to be weighed, which can be very difficult with such small insects because as they move around on the scales, determining their mass can be a challenge.

However, if the antlion larvae were dropped very carefully onto the scales of a balance, they remained in place longer than was necessary for their weight to be accurately recorded.

emeritus Professor Nigel Franks from the University of Bristol's School of Biological Sciences, who led the study, said: “We have decided to use this so-called 'homicide' We found that the length of time individual antlions stay in a particular location is completely unpredictable for each individual.

“This is confirmed when one looks at the duration of immobility after contact in large numbers of antlions. Such data show an exponential distribution. So, just like radioactive atoms, it is unpredictable when an individual will change its state, but the population pattern is perfectly predictable.”

The study shows that the behavior of antlions hiding in plain sight in this way is probably adaptive, since a predator that has picked up and then dropped an antlion larva has no way of knowing how long it will have to wait until its potential victim moves again and becomes a recognizable prey item again. In fact, one of the antlions observed remained completely motionless for over an hour.

Although it is impossible to predict when a motionless antlion will come back to life, this does not necessarily mean that the predator has left the scene to search for alternative prey.

The team'The next question was what animals do after they play dead. In the new study, they show that the behavior of antlions depends on the situation they find themselves in.

Antlion larvae are burrowing animals and may seek shelter by diving into the crumbly substrate where they normally build their burrows. However, it is entirely possible for a predator to drop an antlion onto hard substrate from which it cannot escape.

By using sophisticated automated video tracking of the intermittent movement of individual antlions on different surfaces, researchers have found that the behavior of an antlion after its immobility phase ends depends on the escape strategies available.

Professor Franks added: “Our study may be the first to determine what animals do after they feign death. And we show that their behavior is context dependent. It's a trade-off. So our work opens the field for studying the afterlife in the wide range of animals that exhibit death feigning, thanatosis, or what we prefer to call postcontact immobility.”

Paper:

“Seeking safety: Movement dynamics after post-contact immobility” by NR Franks, A. Worley, GT Fortune, RE Goldstein and AB Sendova-Franks in PLoSOne