Animals living in groups take cues from each other. Freezing or immobilization is a common individual response to danger in many species — seen in vertebrates and invertebrates. Moreover, it can also signal a threat to surrounding animals, a signal that can even be perceived by different species, and it does not attract unwanted attention.   

Now, a pair of neurobiologists have studied the freezing behavior of fruit flies, which is how they respond to imminent danger. Previous work led by one of the researchers, Marta Moita, had found that individual fruit flies either flee or freeze when they face a situation of unescapable danger. This unescapable danger created in the lab was placing the flies in an enclosed transparent chamber and exposing them to an expanding dark disk, intending to mimic an object on a collision course — what the researchers called the “looming stimulus.” 

The pair discovered that the amount of time a fly freezes is linked whether it is alone or in a group, and also depends on the size of the group. The bigger the group of flies, the less they froze. Unexpectedly, they also discovered that resuming movement after freezing works as a safety cue to surrounding flies. They were also able to identify specific neurons that are involved, and intend to continue to investigate the neural circuits involved in freezing and resuming action.