Washington, August 29 : The age-old mystery of how the elusive fly just eludes the swish of the swatter may have finally been solved, with a researcher claiming that aiming a little ahead of where the fly sits prior to the hit will enable you to kill it in one shot.
"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," says Michael Dickinson, bioengineer at the California Institute of Technology (Caltech).
Dickinson has revealed that he and graduate student Gwyneth Card used high-resolution, high-speed digital imaging of fruit flies Drosophila melanogaster faced with a looming swatter to determine the secret to their evasive manoeuvring.
He has found that 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.
The researcher says that all such activities occur 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," he says.
Dickinson says that the videos he has analysed show that if the descending swatter comes from in front of the fly, it moves its middle legs forward and leans back, then raises and extends its legs to push off backward.
However, when the threat comes from the back, the fly moves its middle legs a tiny bit backwards, he adds.
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 says.
"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. Our experiments showed that the fly somehow 'knows' whether it needs to make large or small postural changes to reach the correct preflight posture.
This means that the fly must integrate visual information from its eyes, which tell it where the threat is approaching from, with mechanosensory information from its legs, which tells it how to move to reach the proper preflight pose," he adds.
Dickinson says that his study offers new insight into the fly nervous system, and suggests that there is a map within the fly brain, in which the position of the looming threat "is transformed into an appropriate pattern of leg and body motion prior to take off."
"This is a rather sophisticated sensory-to-motor transformation and the search is on to find the place in the brain where this happens," he says.