illustration by Leif Parsons

Turbo Speed

When a fruit fly detects a looming predator, it can launch itself into the air and soar to safety in just a fraction of a second. But what happens if even a fraction of a second is too long? According to scientists at HHMI’s Janelia Research Campus, flies can employ an even quicker escape response that helps them evade their swiftest predators.

Any threat encountered by a fruit fly will activate a slow and steady takeoff in which it takes time to raise its wings fully.

Janelia Group Leaders Gwyneth Card and Anthony Leonardo and their lab teams recorded the reactions of more than 4,000 flies exposed to a looming dark circle that simulated the approach of a predator. They discovered the flies have two distinct responses: a slow and steady takeoff in which they take time to raise their wings fully, and a quicker, clumsier escape that eliminates this step. “The fly’s rapid takeoff is, on average, eight milliseconds faster than its more controlled takeoff,” says Card. “Eight milliseconds could be the difference between life and death.”

By monitoring neurons in the flies’ brains, the scientists learned that different neural circuits control the two types of takeoff. Any sort of threat will activate the slow, controlled escape neural circuit. But if the threat is closing in quickly—for example, a swooping damselfly—the speedy escape circuit will kick in and override the slow one.

A threat that is closing in quickly will activate a circuit that produces a quicker, clumsier escape.

The findings, published in the July 2014 issue of Nature Neuroscience, help shed light on the neural circuits animals use to select one behavior over another.