The Insane Biology of: The Dragonfly

Hunting from the air is one of the most complex feats of evolution there is. Navigating the world in all three dimensions while outmaneuvering prey that have evolved similarly impressive escape tactics is no small feat. When we think of aerial predators, our mind may go to the fierce birds of prey like the peregrine falcon, who sometimes dive past their prey and then zoom up from beneath it to snatch it mid-air. One study showed they have Other aerial predators, like hawks, single out individual prey birds from their flock, with a similar success rate of 22.5%. Birds like owls hunt by pinning their prey to the ground, lacking well-developed aerial hunting techniques, but still only have a success rate of around 25%. Other dominant predators on Earth rarely exceed these numbers. Lions succeed less than 30% of the time. African dogs are perhaps the best land-based hunters, with a success rate of up to 67% when working together, but this number still pales in comparison to the greatest hunter on Earth. And to find this predator, you have to set your sights to something much, much smaller, hovering near bodies of water, with beautiful wings and huge compound eyes. The dragonfly. Their hunting success rate pushes 100%. Dragonflies belong to one of the oldest insect orders, the Odonata, which have been around for close to 320 million years. Their presence in the fossil record is relatively complete, and shows that their morphology has remained mostly unchanged through time. Their size, on the other hand, has changed dramatically. The ancient dragonflies were giants compared to the ones that exist today. What is it about the dragonfly morphology that led it to be arguably the most effective predator alive today? And if this particular body plan is so effective, why did it gradually get so much smaller over the millennia? Why did evolution rob us of a world where almost one meter long aerial beasts rule the skies? Odonata means toothed ones in Greek, and this fearsome predator's namesake comes from their prominent chewing mouthparts, with sharp teeth found on the underside of their head. Odonates are also characterized for having a freely movable head, very short antenna, large and highly developed compound eyes, three simple eyes, and two pairs of long wings. The only difference between extinct and existing dragonflies is their size. Some Paleozoic species were known to have wingspans exceeding 70 cm, whereas the largest existing species barely exceed a wingspan of 16 cm. Males and females can easily be spotted perching and flying around aquatic habitats, as dragonfly eggs must be laid in water. They generally feed on midges and other small flying insects that inhabit the area, and hunt and eat them in mid-flight. And despite being considered relatively primitive insects, dragonflies possess some of the most unique and spectacular flight adaptations of any animal, allowing them both to reach fast aerial speeds and be incredibly agile. One adaptation they possess is something few other insects do, direct flight muscles. Most winged insects have what are known as indirect flight muscles, which attach to the walls of the thorax, making the thorax deform as they expand and contract. The deformation of the thorax transmits its resonance to the wings, making them vibrate and initiate the flapping motion. Whilst indirect flight muscles have their own advantages, dragonflies instead have individual muscles that attach directly to the base of each of their four wings. Being able to tug on each wing individually enables them to move and direct each of their four wings independently in all three axes, meaning they can control their horizontal, vertical, and torsional motion, granting them precision and agility that is unparalleled by most insects with indirect flight muscles. Thanks to this independent control, dragonflies are one of the few insects that can propel themselves in all six directions, up, down, left, right, forwards, and even backwards. Another remarkable way that dragonfly flight differs from other insects is their ability to flap their fore and hind wings in different phases, and can vary that phase depending on the maneuvers they wish to perform. One flight technique is known as counter-stroking, where they flap their fore and hind wings 180 degrees out of phase with each other. This allows them to hover or engage in very slow forwards flight, and can generate large amounts of lift. For fast forward flight, they're able to switch to phased stroking, where the hind wings beat 90 degrees ahead in phase of the fore wings. While this generates far less lift, it generates a lot more thrust, with some species being capable of reaching well over 50 kilometers an hour, making them by far the fastest flying insects. Dragonflies can also engage in synchronized stroking, which is when the fore wings and hind wings flap together at the same time. This is most useful for increasing their acceleration and to prepare for turning or changing directions quickly. It allows them to generate huge amounts of lift, but can't be sustained for long periods of time, so they generally only use this configuration when chasing prey. In addition, dragonflies are also capable of flying backwards, a flight maneuver which is not possible for almost any other animal, except a few other small types of fly and the hummingbird. They do this by tilting their body upwards at 90 degrees to change the direction of the force generated by the wings. And finally, dragonflies can also choose to not flap their wings at all, allowing them to free glide, take advantage of an updraft, or in the case of some female dragonflies, take a ride with a male who can hold onto her, making him beat his wings to propel the two of them. Being able to switch between such a wide variety of flight behaviors and aerial acrobatics is what makes dragonflies such efficient predators when hunting flying insects, as well as when evading predators of their own. While not exclusive to the Odonata, dragonfly wings also have a prominent pterostigma. It's a small pigmented spot on the leading edge of the wing that is heavier than the rest of the wing. It acts as a counterweight. From a biomechanics perspective, the weight of the pterostigma displaces the cord-wise center of mass ahead of the torsion axis at the level of the pterostigma. If not for this, the outer leading edge of the dragonfly's wing would be prone to self-excitatory flapping and feathering vibrations, known as flutter, which would rapidly stall its flight when gliding at high speed. Such aeroelastic flutter and resonance are phenomena that can endanger far larger structures too, such as aircrafts and even buildings, and is responsible for the 1940 collapse of the Tacoma Narrows Bridge. In the case of dragonflies, a small spot that accounts for less than 0.1% of its total body weight allows them to safely reach a 10 to 25% higher flight speed than they would otherwise. Lastly, a dragonfly's wings are not perfectly flat plates. Their veins form three-dimensional corrugations that make the wing's performance more efficient from a structural perspective. The patterns traced by the veins prevent the wing from warping and deforming as a result of resonance, which enables them to easily alter their angle of attack and generate higher amounts of lift. But it's not just their incredible speed, stability, and maneuverability that makes dragonflies the greatest hunters in the air. It's how they see the world that makes all that agility possible. Dragonflies don't just dominate flight, they have incredible vision. Their characteristic compound eyes are the largest in the insect kingdom. They are made of over 30,000 individual facets or omatidia, which are like mini-telescopes that detect light from the direction in which they point it. As their eyes wrap around their head almost entirely, their field of vision is nearly 360 degrees, perfect for surveying their surroundings for potential targets without having to reorient themselves on their perch. Each omatidia also has 4 to 5 opsins, light-sensitive proteins that absorb different colors of light in the spectrum, and allow dragonflies to perceive color from orange to ultraviolet, which is useful for detecting and courting females using visual signals. With 30,000 omatidia spanning a full 360 degrees, dragonflies do not have the same visual acuity as a human or a bird, but are much more sensitive to movement than we are. A common prey target in the distance will rarely span more than 1 degree across their field of vision before they decide to pursue it, which equates to movement across 2 to 3 omatidia at most, meaning their brain is capable of detecting and processing movement incredibly quickly, so they can immediately pursue prey or avoid a threat. Their eyes are also specialized based on region. The upper or dorsal region of their eye is most sensitive to shorter wavelengths of light, that is ultraviolet and blues. Many dragonflies fly low above the surface of the water when searching for prey, as this allows potential targets to contrast as much as possible with the blue sky. On the other hand, the middle and lower or ventral parts of their eye are sensitive to a wider range of wavelengths. This is likely because color detection is important when identifying and pursuing fellow dragonflies, either as potential mates or rivals, which they are more likely to approach head on or from above. It can also help when identifying prey that doesn't move, such as insects trapped in spider webs, which dragonflies occasionally loot from unsuspecting spiders if no flying targets are available. These vision abilities, combined with their flying prowess, create a formidable predator. However, it's how these two things are integrated that make the dragonfly the most effective predator alive today. It's not just the wings or the eyes that make the dragonfly so successful, but its brain. The dragonfly's brain uses a highly optimized hunting strategy that allows it to predict where the prey is going and to quickly maneuver to intercept it. Studying raptors and other hunting insects has shown that there are two main strategies used by predators to chase down their prey, tracking and interception. And of the two ways to hunt, interception is the far more difficult one. Tracking involves maintaining the target in the same spot in their field of vision and accelerating towards them. The chaser approaches and spirals in towards the prey until its natural advantage in speed allows them to snag it. The other form of hunting is known as interception, where the chaser flies in an intercepting path towards where they predict the prey will be. This is more difficult, as the locations and speeds of the prey and predator must be processed together to make such a prediction. However, if predicted accurately, it's less likely to depend on an absolute speed advantage, which can help the predator to save power as fast forward flight and acceleration is energetically taxing. And even though dragonflies have the speed and agility to be able to engage in tracking if they so desired, they primarily use interception as a form of capture. In humans, interception is a learned behavior. But in dragonflies, it's hypothesized that such behavior must be hardwired into their nervous system, linking their visual system and motor system directly. However, an interception model of pursuit means the prey being hunted is less likely to remain in the same spot within the dragonfly's field of view, which can make the prey more difficult to catch. Studies have shown that dragonflies seemingly adjust their head in near synchrony with their prey, fixing their target in areas of higher visual acuity for tracking. In fact, this synchronization is so perfect that even the head movements appear not to be reactionary, but based on predictions. All of this mind and body integration has given the dragonfly the best hunting record researchers have ever found. In 2012, researchers at Harvard found that dragonflies caught around 95% of the prey they chased. This is impressive for any animal, let alone a flying one. Dragonflies will consume any flying prey roughly the size of their head or smaller, like bees, moths, flies, mosquitoes, or gnats. Larger species will even catch and eat other dragonflies. But if they're the best hunters around, why did evolution push them to hunt small prey? Why couldn't they remain 70 centimeter giants, dominating the skies and snatching up bigger prey? There are two leading hypotheses for the miniaturization of dragonflies, and they're not mutually exclusive. The first is that 300 million years ago, there was much more oxygen in the atmosphere. It's thought that this huge amount of oxygen was able to support larger insect bodies, which rely on passive and active diffusion through holes in their cuticle for respiration. As these oxygen levels decreased to those of the present day, so did the maximum size an insect could reach. The other hypothesis is that small flying dinosaurs and birds, which began evolving 150 million years ago, may have out-competed larger dragonflies for the same ecological niche. Since there is less competition if birds hunt larger organisms and dragonflies hunt smaller ones, smaller dragonflies were more likely to not go extinct. There are very few insects more successful than the dragonfly, who have remained relatively unchanged for hundreds of millions of years. With a killer suite of adaptations to help it maintain top predator status, it's no wonder engineers and scientists alike are keen to study and emulate them. Dragonflies have been the source of inspiration for many biomimicry projects which aim to replicate how they track targets and perform aerial acrobatics. While to date there are no free-flying drones of dimensions comparable to a dragonfly on the market, there are several prototypes of micro unmanned air vehicles in the works. So the next time you see a dragonfly flying around your local pond, remember to take a moment to appreciate this killer in the sky and be thankful they are the size that they are or be glad you're not a fruit fly. As important as dragonfly morphology is to its enduring success as a species, its behavior and the life cycles are equally crucial. Not only do dragonflies dominate the skies, but their larvae are deadly hunters under the water. With their crazy retractable jaws that can shoot out half the length of their body, their world is even more alien than the dragonflies we are familiar with and their hunting strategy even more terrifying. To learn more about the freaky world of dragonflies and their larvae, you should watch Dragons and Damsels on CuriosityStream. It's a 50 minute long David Attenborough documentary that I had never seen before and dives into the murky weird world of these creatures and has amazing close-up footage of their hunting and flying as well as footage of mesmerizing experiments done with smoke to understand the dragonfly's aerodynamics. CuriosityStream is a streaming platform with thousands of high quality documentaries like this one and now CuriosityStream has partnered with us to offer an incredible deal. By signing up to CuriosityStream, you now also get a subscription to Nebula. Nebula is a streaming platform made by me and several other educational YouTube content creators. It's a place where we can upload our videos and podcasts ad-free and a place where we can experiment with new original content. By signing up to the bundle deal, you'll get access to both CuriosityStream and Nebula where you can access originals like TierZoo's Let's Play Outside series with episodes about the cheetah's extraordinary speed or the mantid fly's crazy mashup of traits from both the mantis and the wasp, all of course set in the context of a video game battle. So by signing up at curiositystream.com slash real science, you'll get a subscription to CuriosityStream and a subscription to Nebula for just $14.79 for the entire year. Signing up is also the best way to support this channel and all of your favorite educational content creators. And if you're looking for something else to watch right now, you can watch our previous video about hybrid bears or watch Real Engineering's latest video, The Plane That Will Change Travel Forever, which discusses the blended wing airplane that stands to change how we fly for good.