Do flies fear the fly swat?

Camilla, Duchess of Cornwall, holds up a fly swatter as she is taken on a tour of Brunei Darussalam University. Chris Jackson/Getty Images

Do flies flee from the shadow of a fly swat because they are genuinely fearful or is it just a automatic response? Researchers now believe the flies do fear the shadow.

The flies either increase their speed, freeze as a defence response, or even stop eating in some cases.

The researchers say that when flies flee a shadow it induces a lasting physiological state similar to fear, as opposed to just a momentary escape.

“No one will argue with you if you claim that flies have four fundamental drives just as humans do: feeding, fighting, fleeing, and mating,” says William T. Gibson, a Caltech postdoctoral fellow and first author on the study. “Taking the question a step further — whether flies that flee a stimulus are actually afraid of that stimulus — is much more difficult.”

The study in the journal Current Biology found that the more shadows the flies are exposed to, the longer it takes for them to calm down and return to food.