Ever wonder how flies are so incredibly good at zipping off to avoid that swatter? A new study using high-resolution, high-speed imaging of flies in action has identified an important part of the answer: rather than just taking off, the flies' tiny brains first calculate where the threat is coming from, allowing the insects to carefully prepare themselves to spring toward escape.
This behavior, which effectively plans the flies' take-off, occurs approximately 100 milliseconds earlier than all previously identified components of the escape response, the researchers report online on August 28th in Current Biology, a publication of Cell Press.
"We were surprised to find that 'long'—in fly time—before a fly takes off in response to a predator or swatter it plans the direction of the jump by making a rather complex series of postural movements," said Michael Dickinson of the California Institute of Technology. Those movements carefully position the fly's center of mass relative to the jumping legs so that leg extension propels them away from the looming threat.
"These movements are made very rapidly, within about 200 milliseconds, but within that time the animal determines where the threat is coming from and activates an appropriate set of movements to position its legs and wings," he added. "This illustrates how rapidly the fly's brain can process sensory information into an appropriate motor response."
Those early movements aren't reflexively tied to flight initiation as a fly can get ready for launch and later decide against it, they found. The researchers, noting that the insects could be doing anything at the time—grooming, feeding or walking, for example—also show that when the fly makes planning movements before take-off, it takes into account its starting position.
"The fly somehow 'knows' whether it needs to make large or small changes in its posture to reach the correct pre-flight stance," Dickinson said. That feat suggests that the fly must integrate visual information from its eyes with mechanosensory information from its legs.
Dickinson emphasized the importance of advances in high-speed imaging for making such discoveries possible.
"These instruments have done for the time domain what the electron microscope did for space," he said. "As these instruments become more common, I think we will see that animals perform many behaviors on rapid time scales that simply evaded the detection of our sluggish eyes."
He also hopes the findings in flies will give people a greater appreciation for them, and make them "think before they swat."
The researchers include Gwyneth Card and Michael H. Dickinson, of the California Institute of Technology in Pasadena, CA.