Hunters’ Ballet

One Sunday in late August, an amazing ballet grabbed our attention. In the front yard a swarm of dragonflies whizzed around, filling the air from three to 50 feet above the ground. Outlined against the bright afternoon sky, we watched them hunting, each dragonfly pursuing its own quarry. What were they hunting? Closer inspection revealed that tiny insects, some kind of midge perhaps, were rising from the grass, going straight up into the sky. Tracking an individual midge, it was possible to watch as the midge rose straight up, and a dragonfly spotted it, spun around and then it was gone, snatched into the dragonfly’s mouth or into the basket that the dragonfly made of its legs. This aerial ballet continued, silhouetted against the sky, as the midges played their role in the food chain with hapless persistence.

The dragonflies weren’t chasing the midges. They were intercepting them as they rocketed upward. The midge would rise from the grass and become a black dot against the sky. It would rise and rise and suddenly there was a dragonfly and there was no more black dot midge.

 How do they do that? It takes a sophisticated set of calculations to get the speed and trajectory just right. The dragonfly has several huge advantages over the midge. First of all, they’re bigger—at up to over three inches long, with wing spans of up to 5 inches depending on species.

They can easily eat their body weight in a day of hunting. That happily includes mosquitoes, midges, bees, ants and pretty much anything else that flies. They capture their prey on the wing and snarf it down while they’re looking out for the next one.

Second, they have the largest compound eyes found in the insect world. These two eyes cover most of their head, and come together in the middle. This gives them almost 360-degree vision. Each eye is made up of up to 30,000 facets. Each facet has a lens of sorts, light-sensitive photoreceptors and a neural connection to the insect’s brain. This brain receives up to 60,000 bits of information at any given time and compiles it into a 360-degree map of its surroundings. These facets are all shaped the same and fit together as hexagons, but the photoreceptors in them vary depending on where they are in the eye. This I suppose lets them focus ahead and against a bright blue sky while still being aware of what’s behind or below them. And they can see colors humans can’t. Where people have three types of color receptors for blue, green and red, dragon flies have four or five different color receptors for much more nuanced color detection, including infrared and ultraviolet.

A third advantage the dragonfly has over the midge is its wings. These wings span two to five inches depending on the species with two equal wings on either side. Rather than flap them like most birds do, the dragonfly can control each wing independently and can make them bend, change the angles, and move them backward or forward, stop one or two from moving, or change the relative relationship between any two wings. This gives them tremendous flexibility and maneuverability when hunting. Between their vision and their acrobatics, they catch their prey on the wing up to 95% of the time. They have the requisite six legs, but cannot walk on the ground. They use their legs as a kind of basket to capture large prey instead. 

Engineers imagine cameras that could emulate the dragonfly’s eyes, and airplanes that could fly with the amazing agility of the little creatures. So far, this is only a dream though providing graduate research projects.

Dragonflies hatch in slow-moving streams and marshes, and begin hunting right away as wingless nymphs. They will grow and molt ten to 15 times over the next one to five years before their final escape from the water. At that point they will climb up a plant, shed the last exoskeleton, spread their newly delivered wings and take off.

Alfred Lord Tennyson describes this final transformation like this:

The Dragon-fly

By Alfred Lord Tennyson

Today I saw the dragon-fly

Come from the wells where he did lie.

An inner impulse rent the veil

Of his old husk: from head to tail

Came out clear plates of sapphire mail.

He dried his wings: like gauze they grew;

Thro’ crofts and pastures wet with dew

A living flash of light he flew.

Of the over three thousand species of dragonflies in the world, Iowa claims at least 31 of these “living flashes of Light.”  Which of these 31 species were providing our aerial ballet is hard to tell, since they appeared as silhouettes against the sky. They come dressed in all kinds of brilliant colors and sizes with names that try to match their outfits—black saddleback skimmer, blue fronted dancer, common green darner, white-tail skimmer, eastern amber wing, or ebony jewel-wing. Others are named for their behavior like the autumn meadow-hawk or the pond hawk, as well as several darners, skimmers and gliders. 

One of the largest and most common is the green darner. It grows up to 3.3 inches long with a wing span of some 4.3 inches. It has an iridescent green thorax and head, and a blue underside. The long thin shape of this one and several others earns them the name darner as in a darning needle. One legend has them sewing up snakes when they’re injured. Another has them sewing up the mouths of nagging women, and another sewing the fingers and toes together of people sleeping outside.

Dragonflies are found all over the world, and people have imbued them with supernatural histories and powers. In most of the world, including Japan, China, and the Americas, the bright little hunters are considered good luck, good omens, bringers of wishes and protection against enemies. In some cultures, they are thought to be the souls of ancestors, or to be the Pegasus for the souls of ancestors, coming for a summer visit. But in Europe, the dragonfly was closely associated with the Devil, with bad luck, and as a harbinger of death and misfortune.

On Owl Acres, they’re amazing ballet dancers. Can you imagine being able to fly like that?