Sit quietly by a shallow stream, pond or marsh on a sunny day this summer, and you’ll probably see a remarkable insect: the dragonfly. More than 70 species live in the Washington area. (There are more than 300 dragonfly species in North America!) They lay their eggs in and around water, and they like to perch on wetland grasses and plants. Fossils from 150 million years ago show that these insects haven’t changed much over time. But how much do you know about them? Their life cycle and unusual physical traits deserve a closer look.
As with so much in nature, what you see doesn’t tell the whole story. That beautiful adult dragonfly represents only a small part of the insect’s life span: the last part. An adult dragonfly will live for only a few months. By the time you see it flitting about, it has spent from several weeks to several years as an aquatic nymph in shallow freshwater, breathing through gills, shedding its exoskeleton several times as it grows and feasting on small aquatic critters. Some dragonfly nymphs eat tadpoles or tiny fish.
When it’s time to become an adult, the nymph, called a naiad, crawls out of the water and up a plant stem. It sheds its exoskeleton one last time, unfolds its wings and breathes air. Amazing!
You can identify different species by their patterns and colors. One child, amazed by the bright colors some dragonflies display, nicknamed them “flying rainbows.” What nickname would you give a dragonfly?
Some people call them “mosquito hawks” because they love to gobble up those pesky insects, snatching them in flight. Yay, dragonflies! Some call them “darning needles” because claspers on the end of male abdomens look like sewing needles. The claspers are actually used to hold on to female dragonflies during mating.
Dragonflies have also been referred to as “eye pokers” or “horse stingers,” but you’ll soon see why those are not accurate names.
Like all insects, dragonflies have a head, a thorax and an abdomen. A dragonfly’s abdomen is very long and flexible. Ten jointed segments allow it to bend up and down like a rolling wave.
Despite appearances, dragonflies don’t have stingers and they are harmless to humans and animals. That “horse stinger” nickname probably began because dragonflies go where their food supply is, and flies, gnats and other tasty dragonfly snacks seem to love hanging around horses.
Dragonflies have two huge compound eyes, each with thousands of lenses. (Human eyes have only one lens each.) Dragonflies also have three smaller eyes, called ocelli. They can see in almost a complete circle around them, which is why it’s hard to sneak up on a dragonfly. Local naturalist and educator Kevin Munroe said that if your eyes were proportionately as big as a dragonfly’s, they would “touch the top of your head, under your chin and stretch past your ears.” Imagine what you could see!
Each of a dragonfly’s four wings moves independently of the others. This allows the insect to hover like a helicopter, or move forward, backward and side to side to catch its food in flight and to escape such predators as birds or frogs. It can fly upside down, too!
Notice how transparent the wings are: They look so delicate but are very powerful. They beat about 50 times a second. Some dragonflies zip along at 40 miles per hour! You’ll often see dragonfly symbols on Native American pottery or jewelry because the insect signifies speed and action to some people.
On the front edges of the wings, near the tips, there are little dark rectangular spots called stigmas. These are patches of dried blood inside the wing’s cells; they act like a weight, controlling the wing’s vibrations.
Munroe, who has studied dragonflies closely for more than a decade, says, “Scientists are still discovering new species, even right here in the D.C. area, so you can help by taking photos and keeping notes of what you see.”
Time to start searching!
They really look similar, but the easiest way to tell the difference is to watch them at rest. A dragonfly’s wings are held horizontally, like wings on an airplane, while damselflies rest their wings behind them, in line with their bodies. (See photo above.) The rear pair of wings on a dragonfly are larger than its front wings, but damselfly wings are about the same size. And the two large eyes on most dragonflies touch in the middle. The eyes of damselflies are spaced wide apart.
Check out www.dragonfliesnva.com, a new Web site with lots of information on local dragonflies — how to identify them, where to find them and why they are so fascinating. Even though the site is geared to Northern Virginia, the species covered are found in nearby Maryland and the District of Columbia, too.
To understand how a nymph becomes an adult dragonfly, watch this short BBC nature video. Always ask a parent before going online.