article 6 – Scientists work out best way to swat a fly – 6:20PM BST 28 Aug 2008

By Roger Highfield, Science Editor

Thanks to remarkable flying skills that make the housefly the Ferrari of the insect world, it is unlikely you will achieve a direct hit as they buzz about.

While fleeing a rolled-up newspaper, the insect can change course in as little as 30 thousandths of a second.

Now Prof Michael Dickinson of the California Institute of Technology in Pasadena, who has spent two decades studying flies, announces their ability to escape is all down to quick thinking.

He took high-speed digital video of fruit flies (Drosophila melanogaster) when faced with a swatter, revealing how the creature’s pinpoint sized brain is hard wired to turn the looming shadow into an appropriate pattern of leg and body motion to prime it for a speedy getaway.

Long before the fly leaps, its tiny brain calculates the location of the impending threat, comes up with an escape plan, and plonks its legs in an optimal position to hop out of the way in the opposite direction.

All of this is executed within about 100 thousandths of a second after the fly first spots the swatter, says the study in the journal Current Biology with graduate student Gwyneth Card.

Prof Dickinson suggests the scientific way to swat 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.”.

The videos showed that if the descending swatter – a six inch black disk, dropping at a 50-degree angle toward a fly standing on a platform- 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 backward.

“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,” says Prof Dickinson.

When the threat comes from the back, however, the fly (which has a nearly 360-degree field of view and can see behind itself) 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,” Prof 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.”

This and other flying insects have plagued the worlds of science and engineering ever since the first calculation of bumble-bee flight was attempted at Göttingen University in the 1930s and proved that they should never get off the ground. It is only in recent years that aerodynamics has caught up with bees and other accomplished fliers.

credit: Telegraph.co.uk
extracted date: 09 Novemeber 2009

http://www.telegraph.co.uk/science/science-news/3350498/Scientists-work-out-best-way-to-swat-a-fly.html

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