Don't Bother Swatting a Fly Again, Unless You Are Faster

Author:  Dunia Rassy
Institution:  London School of Hygiene and Tropical Medicine
Date:  September 2008

Our bewilderment as to why flies are hard to swat may have come to an end after a team of Caltech researchers studied closely flies' escape behavior. By following their actions in rapid time scales, through high-resolution high-speed imaging, they found flies perform a series of movements to adjust their posture and avert their predator. The study was published online on August 28th in Current Biology.

According to the study, flies are able to calculate with their tiny brains where the threat is coming from in order to correct the position of their legs and wings. The movements are performed in just 200 milliseconds (0.2 seconds) and do not include the actual take-off. In fact, the fly can later decide against jumping. The main goal of these movements is to modify the fly's center of mass allowing it to extend its legs and propel as far as possible from the swatter. Meanwhile the predator is tricked by the apparent obliviousness of the fly, which might be grooming or feeding at the same time.

The study also highlights the incredible cerebral capacity flies have despite their brains' size. One hundred milliseconds before the swat takes place, flies join visual information along with positional information from their legs. The information is relayed to the brain which almost instantly orchestrates a motor response.

Studying the swift movements would have been impossible without the use of high-speed imaging. On average, one of our blinks takes between 300 to 400 milliseconds and we hardly ever notice them. In contrast to traditional imaging which takes 25-30 frames per second, high-speed imaging may capture up to 33, 000 frames per second. This technology allows the user to analyze movement by displaying high-speed events in slow motion. Michael Dickinson, one of the researchers, added that "these instruments have done for the time domain what the electron microscope did for space".

Dickinson is confident that as high-speed imaging becomes more common, many more animal behaviors that occur on rapid time scales and that have escaped our sight will be exposed. He also hopes that his results will help flies gain more appreciation and make us think next time we plan to swat one.

Written by: Dunia Rassy

Edited by: Jeff Kost

Published by: Hoi See Tsao