Buzz off: Flies have traditionally been difficult to swat, but preempting their crafty behaviour could help to strike them more effectively.
Credit: iStockphoto
SYDNEY: Using high-speed video footage, bioengineers have discovered the key to the evasive manoeuvrability of flies – and found the best strategy for swatting them successfully.
Michael Dickinson has been interviewed hundreds of times about his research on the biomechanics of insect flight. One question has always dogged him: Why are flies so hard to swat?
"Now I can finally answer," said Dickinson, a bioengineer at the California Institute of Technology in Pasadena, USA.
Tiny brain, big escape plan
Using high-speed, digital imaging of fruit flies (Drosophila melanogaster) faced with a looming swatter, Dickinson and graduate student Gwyneth Card determined the secret to a fly's crafty behaviour.
Long before the fly leaps, its tiny 'brain' 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. All of this action takes place within about 100 milliseconds after the fly first spots the swatter.
"This illustrates how rapidly the fly's brain can process sensory information into an appropriate motor response," said Dickinson who this week publishes a paper detailing the research in the U.S. journal Current Biology.
In this study, the swatter was actually a 14-centimetre-diameter black disk, dropping at a 50º angle toward a fly standing at the centre of a small platform.
The researcher's videos show that if the descending swatter comes from in front of the fly, the fly moves its middle legs forward and leans back, then raises and extends its legs to push off backward.
Rear attack
When the threat comes from behind, however, the fly (which has a nearly 360º field of view) moves its middle legs a tiny bit backwards. With a threat from the side, the fly keeps its middle legs stationary, but leans its whole body in the opposite direction before it jumps.
"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.
"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, like grooming, feeding, walking, or courting," he said.
Perfecting pre-flight posture
Yet, the experiments hinted that the fly somehow 'knows' whether it needs to make large or small postural changes to reach the correct pre-flight posture. This means that it must integrate visual information from its eyes with sensory information from its legs, to tell it how to move to get in the optimal pose for take-off.
The results offer new insight into the nervous system of insects, and suggest that within the fly brain there is a map in which the position of the looming threat "is transformed into an appropriate pattern of leg and body motion prior to take off," Dickinson said. "This is a rather sophisticated sensory-to-motor transformation and the search is on to find the place in the brain where this happens."
Handily, the research suggests an optimal method for successfully swatting a fly.
"It is best not to swat at the fly's starting position, but rather to aim a bit forward of that to anticipate where the fly is going to jump when it first sees your swatter," suggested Dickinson.
With the California Institute of Technology.
