Jonathan Peterson ‘23
Co-Executive Editor
You’ve likely encountered the subject of this article. Perhaps it was in your garden, perhaps it was while fishing, perhaps it was just on a walk. What you likely did not realize is that you encountered the most efficient and successful predator on Planet Earth.
Hunting Success
When dragonflies choose to hunt, they are unparalleled in the animal kingdom. Birds of prey, like peregrine falcons, are typically what we think of as the peak of aerial hunting. Their success rate, or the percent chance that they catch their target, sits at roughly 25 percent. Lions, one of the most formidable land predators, sit pretty at about 30 percent. And African painted dogs are at the peak of land predators when it comes to efficiency, blowing their competition out of the water with a staggering 67-percent success rate.
Dragonflies, however, are another story altogether. When a dragonfly takes wing, its success rate is as high as 95 percent. So, what enables these tiny death machines to be the coldblooded killers that they are?
Physical Traits
Dragonflies have remained relatively unchanged for the last 300 million years. In terms of their physical traits, the only one that has changed substantially is their size—they used to be much larger.[1]
The first key to dragonflies’ success is their direct flight muscles. Unlike many other insects, which have indirect flight muscles, dragonflies can independently control each of their four wings. This enables them to beat their wings in multiple different patterns, or “phases.” Different phases allow for different forms of flight. In fact, not only can dragonflies fly over thirty miles per hour, depending on the phase, but they can also fly in all six directions.[2] This makes them both one of the most maneuverable animals in the world,[3]and the fastest flying insect on the planet.
They can reach these high speeds thanks to a special, pigmented section on the leading edge of their wings called a pterostigma. This pigmented section of the wing is heavier than other, similar segments of the wing. This acts as a counterweight and, at high speeds, provides stability. Essentially, it prevents the leading edge of the wing from fluttering.[4] This small feature enables dragonflies to fly somewhere between 10 and 20 percent faster than they would otherwise be capable of.
Dragonflies also have the largest compound eyes of any insect, giving them full 360-degree vision. Their eyes are made up of over 30,000 ommatidia, or smaller, hexagonal eyes. These 30,000 smaller eyes make up the larger compound eyes they are a part of. Further, different parts of the dragonflies’ compound eyes are sensitive to different wavelengths of light. For example, the top of a dragonflies’ eyes—the part that faces the sky while they fly—is more sensitive to shorter wavelengths like blues and ultraviolet light. The middle and lower portions of the dragonflies’ eyes are sensitive to a wider spectrum, giving them a better sense of overall color when looking at something beneath or in front of them. There is a very real reason for this—when flying, their prey often appears above them. By being sensitive to shorter wavelengths of light, like blues, the top of their eye is better able to see prey items contrasted against the blue sky—the prey stands out more because the dragonfly is better at seeing blue. And dragonflies typically encounter predators, mates, and other cannibalistic dragonflies either directly ahead of them or beneath them. Being able to see a broader spectrum of colors in those ranges allows them to identify friends and foes much more quickly, while maintaining the ability to see prey items above them easily.
Maybe She’s Born with It
All these physical traits are not the deciding factors in what makes dragonflies such successful hunters—they are merely constituent factors. Dragonflies bring these lethal skills together in such an effective way thanks to how they process the world.
There are two methods of aerial hunting: tracking and interception. Of the two, interception is the far more complicated and rare method. Tracking involves chasing down a target and using speed and agility to overwhelm them. It is incredibly physically taxing. Dragonflies, with their speed and agility, would certainly be incredible trackers.
Interception, on the other hand, is a predictive method of hunting. Interception involves seeing an animal’s path, predicting where the animal will be at a given time, and meeting the target there. In humans, interception is a learned trait. Try intercepting a softball in the outfield and you’ll realize just how hard it is. Or watch a three-year-old chase a soccer ball—it’s comical how poor we are at it. However, in dragonflies, interception is hardwired into their nervous system. This means that their motor system (how dragonflies move their body) and nervous system are wired together, allowing dragonflies to, essentially, do geometry instinctively. Not only this, but their heads independently and synchronously move with their body as they fly to keep their target within the appropriate range of vision.[5] This head movement has also been shown to be what I refer to as instinctual geometry.
Conclusion
I hope this article will give you a newfound appreciation for dragonflies—they are beautiful animals with a complex and intriguing physiology. And perhaps I’ve also given you something else to be thankful for this November: the fact that meter-long dragonflies no longer exist.
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jtp4bw@virginia.edu
[1] I’m talking meter-long dragonflies here. Absolute units.
[2] Up, down, left, right, forwards, and backwards. I’m unsure whether dragonflies can reach equivalent speeds in all directions.
[3] Only a few other types of flies and hummingbirds can fly backwards.
[4] If you hold onto the edge of a piece of paper and try to swing the entire piece through the air, it will flutter at the leading edge. Thepterostigma essentially enables the wing to slice through the air, as opposed to fluttering, like that piece of paper.
[5] Top, middle, or bottom.