High-resolution, high-speed digital imaging of fruit flies faced with a looming swatter shows the fly "calculates the location of the impending threat, comes up with an escape plan, and places its legs in an optimal position to hop out of the way in the opposite direction" within about 100 milliseconds after the fly first spots the swatter, said Michael Dickinson, a professor of bioengineering at Caltech.

"We also found that when the fly makes planning movements prior to take-off, it takes into account its body position at the time it first sees the threat," Dickinson said in a release. "When it first notices an approaching threat, a fly's body might be in any sort of posture depending on what it was doing at the time."

Dickinson said the best way to swat a fly is to aim a bit forward of the fly's starting position to "anticipate where the fly is going to jump when it first sees your swatter."

The findings are published in the journal Current Biology.