A fly buzzes past your head and lands nearby; you snatch a pilot or roll up a magazine and approach carefully – and you strike!
But no matter how fast you are, the fly is almost always faster, and it usually manages to dodge your wallop and escape unscathed. (Is it trying to irritate you ?!)
Flies have many adaptations that give them increased speed, agility and perception, making them very, very good at detecting and evading even the fastest swats. And new evidence shows that flies’ modified hind wings play an important role in the rapid takeoff – often only in the short term.
Related: 7 amazing bug ninja skills
Houseflies (Musca domestica) belongs to the order Diptera, or true flies. Diptera flies have modified hind wings that have developed into sticky structures with a knob at the end called halter nests. Their vibrations help the insects to stabilize their bodies while flying, by observing body rotations and transmitting information to the wings.
Flies in the Diptera subgroup Calyptratae, which includes houseflies, also vibrate their dumbbells as they walk, but scientists did not know why. In a study published online in the journal on January 13, 2021 Proceedings of the Royal Society B: Biological Sciences, researchers examined Calyptratae flies to determine whether dumbbell oscillation affected their transition to air, which led to additional sensory input to help coordinate movements in the wing and leg muscles.
Using high-speed cameras to capture captured and free laboratory-sized flies during takeoff, the scientists made recordings at speeds of up to 3,000 frames per second. They found that Calyptratae flies launched themselves five times faster than other flies; their takeoffs require on average about 0.007 seconds (7 milliseconds) and only one flybeat.
‘None of the Calyptratae have an ascent time longer than 14 milliseconds [0.014 seconds], “the researchers reported. In comparison, the takeoffs of non-Calyptratae flies lasted about 0.039 seconds (39 milliseconds) and according to the study, it was about four flight beats.
The researchers then removed the dumbbells, which all Diptera flies have. Calyptratae flies without these lumpy structures took much longer to become in the air, but the start-up time was not affected in non-Calyptratae flies without dumbbells. Stability during takeoff also suffered with dumbbell removal, but only in flies from Calyptratae. The Calyptratae insects, known as bladder flies that tried to fly up without their dumbbells, ‘always caused a crash’, the scientists reported.
“Halter use therefore allows for greater speed and stability during rapid escapes – but only in the Calyptratae clade,” the scientists wrote in the study.
In the blink of an eye
Halteres are not the only secret weapon in a fly’s elusive arsenal; once a fly is in the air, it can perform maneuvers that would be the envy of a fighter pilot. Fruit flies can change course within 1/100 second – about 50 times faster than an eye can blink, Live Science reported earlier. In experiments, perfectly fixed wing flaps generated enough force to quickly propel the flies away from a predator while in the air.
“These flies roll up to 90 degrees – some are almost upside down – to maximize and escape their power,” said Florian Muijres, who studied the biomechanics of flight at the University of Washington in Seattle, and now at Wageningen University and research in the Netherlands, Live Science told in 2014.
Flies also have an exceptional vision, which helps them plan their jumps from a threat. About 200 milliseconds before takeoff, fruit flies use visual input to modify an impending danger to adjust their posture and indicate the direction they will take to safety, scientists wrote in 2008 in the journal Current biology.
In fact, their improved perception juggles up to six times more visual input in one second than humans can, reported the BBC in 2017.
Animal brains observe the passage of time by processing images at a velocity known as the “flickering fusion rate”, a term that describes how many images per second flash in their brains. Roger Hardie, emeritus professor of cellular neuroscience at the University of Cambridge in England, implanted electrodes in the photoreceptors of flies’ eyes to measure their flickering fusion and calculate it 400 times per second; the average flickering speed for humans is around 60, according to the BBC. This means that movement that you consider “normal” moves like slow-motion to a fly.
With all these built-in benefits, it’s no wonder the fly you’re trying to swing can escape. One approach that can improve your chances, however, is to direct your swat to a place where the fly is likely to go, rather than where it rests, said Michael Dickinson of the California Institute of Technology in Pasadena. The Independent in 2011.
“It’s best not to swing the fly’s starting position,” Dickinson said. “Aim a little ahead to anticipate where the fly will jump.”
Originally published on Live Science.