Fruit flies manoeuvre like fighter jets to escape threats

Thursday 10 April 2014 20.37
The flies used in the research are about the size of a sesame seed (Pic: Floris van Breugel and Florian Muijres)
The flies used in the research are about the size of a sesame seed (Pic: Floris van Breugel and Florian Muijres)

Threatened fruit flies behave like tiny fighter jets, research in the US has shown.

Scientists in the US used high-speed video cameras operating at 7,500 frames a second to capture the astonishing displays.

"Although they have been described as swimming through the air, tiny flies actually roll their bodies just like aircraft in a banked turn to manoeuvre away from impending threats," said Professor Michael Dickinson, from the University of Washington.

"We discovered that fruit flies alter course in less than one one-hundredth of a second, 50 times faster than we blink our eyes, and which is faster than we ever imagined."

The videos showed that in the middle of a banked turn the flies could roll on their sides at an angle of 90 degrees or more, sometimes almost flying upside down.

"These flies normally flap their wings 200 times a second and, in almost a single wing beat, the animal can re-orient its body to generate a force away from the threatening stimulus and then continue to accelerate," said lead author Florian Muijres.

He also works at the University of Washington.

The flies used in the research, a species called Drosophila hydei, are about the size of a sesame seed and rely on an incredibly fast visual processing system to detect approaching danger.

The scientists studied their escape ability by using an expanding shadow to mimic a looming predator.

Their cameras were focused on a small area in the middle of a cylindrical flight arena where 40 to 50 flies flitted about.

When a fly passed through the intersection of two laser beams at the centre of the arena, it triggered the appearance of the shadow.

An array of infra red lights was used to illuminate the scene to avoid the flies being blinded.

The results appear in the latest edition of the journal Science.

As they make their fast getaways, fruit flies pitch and roll their bodies at the same time, the study showed.

In contrast, when flying steadily and not threatened, they behave like a plane making small course corrections with its tail rudder.

(Pic: Florian Muijres)

The banked escape manoeuvres are about five times faster than the flies' normal in-flight turns.

How the fly's minuscule brain is able to detect a threat, decide on the best course of evasive action, and execute the manoeuvre so fast remains a mystery.

"The brain of the fly performs a very sophisticated calculation, in a very short amount of time, to determine where the danger lies and exactly how to bank for the best escape, doing something different if the threat is to the side, straight ahead or behind," said Prof Dickinson.

"How can such a small brain generate so many remarkable behaviours? A fly with a brain the size of a salt grain has a behavioural repertoire nearly as complex as a much larger animal such as a mouse.

"That's a super interesting problem from an engineering perspective."

The scientists captured details of 3,566 individual wing beats from 92 fruit fly escapes and recreated many of them using small flapping robots.

(Pic: Florian Muijres)