Killer flies ‘dive bomb’ at their prey, but often loses control in the air and misses their target, a new study finds.
A team of researchers led by the University of Cambridge filmed the species with cameras as it tried to catch prey in transparent tanks in the lab.
The species, Coenosia attenuata, can reach accelerations in excess of 3 g in air diving to catch their prey, they found.
But at such high speeds, they often miss because they cannot correct their course and end up awkwardly recalibrating in mid-air.
Incredibly, the species, which is native to southern Europe, travels five times faster than a falcon, despite being 0.1 inches in length.
The study was conducted by researchers from the University of Cambridge, the University of Lincoln and the University of Minnesota.
“Insects that are older in the air usually contrast their prey with the sky and attack from above,” they say in their paper.
However, killer flies (Coenosia attenuata) can attack prey flying beneath them and perform what we call “air diving.”
“Killer flies are fast and highly maneuverable dual predators that hunt down and up flying prey.”
Pictured, front and side view of the deadly fly (Coenosia attenuata). Killer flies are fast and ‘highly maneuverable’ predators, which hunt prey that flies both down and up
The high speed air dives are achieved through a combination of gravity and wing flapping, or ‘active muscle acceleration’.
This is akin to people cycling down a hill instead of just being helped by gravity – a situation that would likely lead to a loss of control as well.
It allows the species to reach impressive accelerations of up to 36 m / s2, which is equivalent to 3.6 times the acceleration due to gravity (or 3.6 g).
THE KILLER FLY
The killer or hunter fly (Coenosia attenuata) is a type of fly native to southern Europe.
They are found in Spain, France, Italy, Germany and Greece.
They prey on fruit flies, whiteflies and other smaller insects.
Killer flies are fast and ‘highly maneuverable’ predators that hunt down and up flying prey.
Researchers say it is the only insect to fall down.
It uses a combination of gravity and ‘active muscle acceleration’ – wing flaps – to trigger high dive bombardments.
This is comparable to people cycling down a hill instead of just being assisted by gravity.
Amazingly, diving falcons, the fastest creatures to catch their prey in mid-air, achieve much lower accelerations of just 6.8 m / s2.
Falcons dive by folding their wings and accelerating by gravity towards their prey.
But the killer fly doesn’t account for the effect of gravity when diving to intercept a target, the researchers say.
To get their results, the international team built a transparent ‘flight arena’ and flew a dummy prey target through it at a constant speed, as well as real fruit flies (the deadly fly’s prey).
Killer flies were filmed with high-speed video cameras as they attacked the target, and the researchers watched the footage in slow motion.
The research team then used this data to reconstruct the entire series of attacks in 3D.
They found that the flies achieved much higher accelerations in flight when taking off from the ceiling of the arena, compared to the floor or walls.
The flies beat their wings at the same speed wherever they came from, indicating that their flight speed is determined by a combination of wing force and gravity.
“When deadly flies took off from the arena floor or walls, they moved as soon as they could take the shortest path to the target,” said study author Sergio Rossoni, a PhD student in the Department of Zoology at the University of Cambridge.
“But they couldn’t when they took off from the ceiling, because the high acceleration due to gravity changed the expected flight path.”
Killer fly with its prey. Killer flies can reach accelerations of 3.6 g in air dives to catch their prey
Diving at a super high gear, the killer fly sometimes catches its prey extremely quickly, but it often misses because its speed makes it difficult to change course mid-dive if the prey is moving.
However, even if the fly does not land on the target, the species can keep an eye on its prey at close range as it performs the final maneuvers to capture it.
High speed dives also force the potential prey to change direction as the attacker approaches, but to do this the prey must slow down, making it easier to catch.
Rossoni said his team was interested in the deadly fly, also known as the hunter fly, because it is the only insect to attack down.
A still from the video above shows the larger deadly fly just as it misses a real fruit fly – then zooms past. Rossoni said, “You can see the fruit fly turning a lot in an attempt to escape the deadly fly. Doing this slows down the fruit fly, allowing the killer fly to get closer and closer until it is caught ‘
Insects that hunt in the air usually attack their prey upwards, as the contrast of the prey with the air makes it easier to see them.
“Normally, insects attack from above because they can silhouette prey against the clear sky and it is less cluttered,” he told BBC Radio 4’s Today program Friday morning.
“But deadly flies are special because they attack in all directions.”
Killer flies, therefore, are uncommon insect predators, as it is more difficult to hunt down against a visually messy ground, with eyes that are only coarse resolution.
“The difficulty of hunting prey against the messy ground is compounded by the coarse resolution of the deadly flies’ eyes, which is poor even when compared to other predators,” the team said.
Under such conditions, it is possible to dive for prey at high speed, despite the associated reduced maneuverability.
‘By reducing the distance to their targets, killer flies also increase the target’s angular size on their retina, making it less likely to lose sight of it’
The findings are published in the Journal of the Royal Society Interface.
Fruit flies are ‘extreme ultramarathon kites’, according to research
Although they are best known for buzzing in circles in search of bananas, scientists reveal that fruit flies have a very impressive range.
The species, Drosophila melanogaster, can fly up to nine miles (15 km) in one trip, researchers at California Institute of Technology (Caltech) report.
Impressively, this is about 6 million times their average body height, which is just 2.5 millimeters or one-tenth of an inch.
This would be the same as the average human who travels just over 10,000 kilometers in a single trip – roughly the distance from the North Pole to the equator.
“The dispersal power of these tiny fruit flies has been hugely underestimated,” said study author Michael Dickinson, a biologist at Caltech.
For the experiments, the team placed 10 ‘scent traps’ in a circular ring, each located along a radius of one kilometer (0.6 miles) around the release site.
Each trap featured an enticing cocktail of fermenting apple juice and champagne yeast – a combination that produces carbon dioxide and ethanol, which are irresistible to a fruit fly.
Read more: Hungry fruit flies can fly up to 14 miles in a single trip to find food