How Flies Quickly Escape Looming Predators: Avoiding Danger

Fruit flies are masters of evasive action. When they sense a predator, it takes them just a fraction of a second to launch themselves into the air and buzz to safety. Now, scientists have uncovered how these insects are so adept at avoiding danger. It turns out that there's a quick-escape circuit in the fly's brain that gives them a leg up over their predators.

"The fly's rapid takeoff is, on average, eight milliseconds faster than its more controlled takeoff," said Gwyneth Card, one of the researchers, in a news release. "Eight milliseconds could be the difference between life and death."

Scientists have long suspected that a pair of neurons, called giant fibers, in the fruit fly brain can trigger the insect's escape. In fact, researchers can provoke this behavior by artificially activating the giant fiber neurons. That said, no one had actually demonstrated that these neurons responded to visual cues associated with a predator.

In order to better understand these giant fiber neurons, the scientists developed a way to switch the giant fiber neurons on and off. They then watched how the flies responded to a predator-like stimulus. Then, they recorded the flies' responses with a high-speed camera that works at 6,000 frames per second. In all, the researchers analyzed more than 4,000 flies.

So what did they find? It turns out that there were two distinct responses for a simulated predator: long and short escapes. For a steady takeoff, the flies took their time to raise their wings fully. For a quicker escape, though, the flies eliminated this step and shaved time off of their takeoff, but sometimes tumbled through the air because of it. The scientists also found that even when the giant fiber neurons were switched off, the flies still managed to complete their escape sequence.

"On a surface level evaluation, silencing the neuron had absolutely no effect," said Card in a news release. "You can do away with this neuron that people thought was fundamental to this escape behavior, and flies still escape." That said, the shorter escapes were completely eliminated, which means that it could mean that they'd be less effective at escaping.

The findings reveal a bit more about this escape behavior. This could shed light on the powerful system that animals use to select one behavior over another.

The findings are published in the journal Nature Neuroscience.