Have you ever felt frustrated after repeated attempts to swat a buzzing insect have failed? You’ve slapped yourself and the table many times, yet the fly continues to taunt you?
Flies’ impressive agility inspired a team of scientists from the University of Washington worked with some aerospace engineers at the Delft University of Technology to carefully study the biomechanics of how the insects execute their evasive maneuvers. They discovered that to avoid looming predators or human swatting, fruit flies can rapidly make banked turns, executing them far faster than their regular flight movements.
To study fruit fly flying technique, they constructed a test environment with high-speed cameras capable of recording 7,500 frames per second. The testing area was lit with LED lights that could be triggered to create a dark, expanding circle that the flies would interpret as a looming predator. The scientists filmed almost 100 trials in this setup, which included 3,655 individual wing beats. A special vision-tracking system analyzed the images, studying the position of the flies' body and wings separately. It measured flight speed, acceleration, and three angular measurements of body and wing position.
Much like an airplane, a fly’s body can move in three dimensions: yaw (rotating along a vertical axis to change direction), pitch (tilting the head up or down), and roll (turning the body left or right).
Once the flies detected a threat, they “altered their flight path in a remarkably fast and accurate manner,” the authors found. What’s remarkably fast? Fewer than two wing beats. These flies beat their wings 200 times per second, so that’s less than a hundredth of a second. Hence the high-speed cameras.
In normal flight with no threat detected, the flies tend to turn in the same way an airplane does when it's using its tail rudder to shift direction while maintaining a constant speed. They manage this by rotating on their yaw axis. But for evasive turns, the flies shift direction fives times as fast. They pitch and roll in a way that would probably make some of the passengers on an airplane reach for their barf bags. The flies rotate their bodies in one direction and then rotate back within just a few wing beats, using torque and counter torque to bank like a fighter jet.
That’s why you can’t swat them. Don’t think brainless bug. Think highly advanced military technology. You’ll feel better.
Studying the wings revealed that subtle, coordinated changes in motion create these aggressive turns.
Fruit flies have very small brains, but the findings demonstrate that the insects must have some very well-developed, rapid-firing sensory motor circuits in order to register and respond to the visual threat of predators so fast and effectively.
The authors propose that genetic and physiological studies with related species could shed light on the nervous system and physiology that gives fruit flies the ability to make these rapid movements.