So often we see scientists turn to the natural world for ways to improve robotics, and new research may soon be drawing their gaze toward the so-called robber fly. It only measures 6 mm (0.25 inch) in length, but this little critter has a remarkable ability to spot and capture its prey, even when it requires a swift, last-minute change of direction. So much so, that scientists have labeled this supremely talented hunter the Top Gun of the fly world.
The robber fly, or Holcocephala, is around the size of the average mosquito. But what really interested researchers at the University of Cambridge was its impressive ability to spot and quickly catch prey at distances that bely its diminutive size – more than half a meter away (1.6 ft) and within half a second. In human terms, that would be the same as us seeing and catching prey at the other end of a soccer field in the same time frame.
So the team ran some experiments that allowed them to study this phenomenon up close, setting up high-speed video cameras and watching as a robber fly hunted fake prey (a small bead on a fishing line). When it first spied the prey, it launched itself upwards and kept what is known as a constant bearing angle, meaning that it maintained the same orientation as it moved in for the kill.
"If you think of this as though you're driving along the motorway and a car is coming down the slip road, then if the relative angle between you and this car remains constant, you will collide," explains PhD student Sam Fabian, a researcher on the project. "Of course, you'd take evasive action, but in the case of the robber fly, this is what it wants."
Zeroing in on its food in this way means that the robber fly is able to quickly change direction if needed. The team demonstrated this last-minute agility by changing the direction of the bead when it was in mid-flight, watching as the fly adjusted its flight path accordingly. And while they are unsure how the fly measures the distance, the team also found that when it is around 29 cm from the prey (0.95 ft), it locks on while making a change to its own trajectory, slowing down and pulling up alongside for a final, deadly lunge.
"What you see is similar to a baton pass in a relay race, when the two runners are heading in a similar direction and speed, they are more likely to be successful than if they are passing each other at ninety degrees," says Dr Trevor Wardill, lead author on the paper.
Using microscopic imagery, the team investigated the reasons for these elite hunting skills. It found that the robber fly has eyes made up of thousands of lenses, but its largest are as big as the dragonfly's, believed to have the best vision of all insects. The thing is, however, a dragonfly is 10 times larger.
"There's a trade-off going on between having excellent vision — which requires bigger lenses — and the size of the insect," says Dr Paloma Gonzalez-Bellido from Cambridge's Department of Physiology, Development and Neuroscience. "The only way a robber fly could have vision as excellent as the 'poster child' of predatory insects, the dragonfly, across its entire visual field, would be to have an eye with many more and larger lenses — but then the fly itself would need to be much larger to be able to carry it."
What the team found was that the largest lenses were concentrated in the center of the eye while smaller lenses sit around the outside. And beneath the larger central lenses, the fly has evolved extremely small light detectors. These sit almost parallel with each other and are much further away from the lens than is normally found in insect eyes. The scientists say it this unique arrangement that allows for the high, almost dragonfly-like resolution.
Packing such powerful vision into such a small package could have lessons for the world of drones, where processing visual information can require large amounts of energy. If these capabilities can be harnessed to improve drone technology, we could see unmanned aircraft with improved visual sensors that can better allocate their limited battery power.
"The problem with drones is often one of the battery power necessary for accurate image processing," says Dr Gonzalez-Bellido. "The processing power is a huge drain on resources. But as is often the case, we can take lessons from the natural world to minimise the power requirements. This, combined with the robber fly's remarkable hunting ability, could help in the design of drones designed to take down illegal drones near airports, for example."
The research was published in the journal Current Biology, while you can hear from the researchers in the video below.
Source: University of Cambridge
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