The dragonfly is a fearsome-looking insect that predates the dinosaurs and also happens to be a flying marvel.
Window On Nature
By Lowell and Kaye Christie, F47246
September 2009
Summer afternoons might seem an unusual time to watch critters, but in addition to observing birds and mammals, we enjoy studying insects. We often beat the heat on a sunny day under a shady tree next to a small pond or a meandering stream. As we relax, we get to watch the antics of one of the oldest insect species living today “” the dragonfly.
They’ve been around since before the dinosaurs, with the earliest fossils discovered in Upper Carboniferous sediments of Europe that formed more than 325 million years ago. Of course, things were a little larger then. One dragonfly relic was found with a wingspan of 28 inches. But, except for size, dragonflies haven’t changed all that much.
The dragonfly is a hunter, eating almost anything of an appropriate size that flies by, including smaller dragonflies. They are one of the quickest and most maneuverable creatures you’ll find, with a body structure designed for their lifestyle.
Other insects flap a single pair of wings in unison (think butterflies and bees), but the dragonfly has two pairs of wings that can be moved independently. Watch closely and you can sometimes see the back wings going down as the front wings come up. This allows the dragonfly to fly forward, backward, and hover for as much as a minute. According to research done by folks at the University of California Museum of Paleontology, dragonflies can travel approximately 100 body-lengths per second, and one species from Australia was clocked at 36 miles per hour.
Dragonflies rival birds in their coloration, coming in shades of pink and blue, gold and black, emerald and maroon, with some species boasting metallic shades that glitter in the sunlight. Perhaps the most striking feature is their eyes.
From a front view, dragonflies seem to be mostly eyes. On some species the two eyes are so large and so close together they almost cover the head. The compound eye is made up of as many as 30,000 facets, each facing in a slightly different direction, giving the insect a composite view of its entire surroundings. A dragonfly uses up to 80 percent of its brain coordinating all these images.
The dragonfly eye sees more colors than the human eye and can even distinguish ultraviolet light. Its compound eye is designed so the upper portion views only blue and ultraviolet, which makes the sky appear lighter, causing small flying objects to appear darker “” another adaptation to improve hunting skills. The dragonfly’s sight is so sensitive it can respond to stimuli as much as 40 feet away. That’s why it is so difficult to sneak up on one.
You can use the size and shape of the eye to distinguish the dragonfly from other insects, and also from the closely related damselfly. There’s a bit of confusion here, because the damselfly and the dragonfly are the two subdivisions of the Odonata order of insects and look very much alike. However, the damselfly is smaller and flies more slowly. Also, the dragonfly’s eyes meet on the top of its head, but the damselfly’s eyes are widely separated.
Differences also exist in the wing structure, but from the observer’s point of view, the way the two insects hold their wings when at rest is the best identification. Neither the dragonfly nor the damselfly can actually fold its wings over its body, because the wing veins are fused at the base. However, the damselfly can hold its wings parallel to and above its body, while the dragonfly keeps its wings extended to the side like those on an airplane.
The life cycle of both the dragonfly and damselfly are quite similar. The male, usually more colorful than the female, patrols an area of water that seems to offer a good egg-laying environment. When a female approaches, the two join in a circular shape called a “mating wheel,” often flying attached for anywhere from a few seconds to several minutes. Then the female, sometimes attended by the male, deposits her eggs by inserting them into vegetation with an ovipositor or, in some species, by spreading them on the water.
The eggs hatch into aquatic larvae called nymphs, and remain in that stage for anywhere from months to years, depending on the species and the climate. The young nymph, like the adult, is a hunter and will eat almost anything that comes along.
The nymph sometimes stalks its food, but often is an ambush hunter, depending upon its camouflaged coloration to attack other insects and even small fish. The dragonfly nymph has a grasping lower lip that shoots out to capture prey. It can extend almost the length of the nymph’s body and hits its target in less than a second.
After shedding its skin many times, the nymph eventually leaves the water and with its final molt takes on the form of an adult dragonfly. Like butterflies emerging from a chrysalis, dragonflies must pump up their wings and allow their bodies to harden. A few days pass before they take on the bright coloration of the adult dragonfly. Although a few species of dragonfly migrate and live for months, a few weeks is a more typical lifespan. But during those few weeks, the life cycle for the next generation begins.
To watch dragonflies, we use close-focus binoculars rather than the ones we normally carry for bird-watching. Dragonflies are quite large for insects, but you still have to be fairly close to get a good look.
There’s a trick to achieving the best view or capturing a good picture. First, determine the closest distance at which your binoculars will focus. Then force a tall stick into the pond or stream bank so the tip extends over the water and is located just at the focus distance from where you want to sit. If the stick is slightly higher than the surrounding vegetation, there’s a good chance a local dragonfly will decide to use it as a perch when it grows tired of patrolling the area.
A shady spot to sit, a cool breeze coming off the water, and some insect entertainment “” what more could you ask for?