When a fly escapes being swatted, what is going on in its head? Is it as terrified as we would be after a close shave with death? Or is buzzing away from assailants a momentary inconvenience that flies shrug off? It now seems that flies do become rattled.
“In humans, fear is something that persists on a longer timescale than a simple escape reflex,” says William Gibson of the California Institute of Technology in Pasadena, California. “Our observations suggest flies have a persistent state of defensive arousal, which is not necessarily fear, but which has some similarities to it.”
This doesn’t mean that flies share the same emotional responses to fear as humans, but they do seem to have the same behavioural building blocks of fear as us.
Gibson and his colleagues exposed fruit flies to overhead shadows resembling aerial predators, such as birds. The more shadows they were exposed to, the more the flies resorted to evasive behaviour, such as hopping, jumping or freezing.
“The more shadows we used to disperse them from the food, the longer they took to ‘calm down’ and return to the food,” says co-author David Anderson, also at Caltech.
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