Insects, with few exceptions, rank up there with spiders and snakes as being among the least appreciated creatures of the wild. One of those exceptions, however, is the dragonfly. Along with butterflies, dragonflies fascinate and capture our imaginations. No doubt, their prowess as aviators has a lot to do with that fascination. Dragonflies flit and dart to and fro, up and down, hovering and zigzagging. Their aerial movements are the envy of human pilots and aeronautical engineers everywhere – their ability to catch (and devour) flying insect pests is nothing short of amazing.
Dragonflies, and their smaller cousins, the damselflies, are members of the insect order Odonata. True dragonflies belong to the suborder Anisoptera, while the damselflies belong to the suborder Zygoptera. The two groups can be distinguished by a variety of different traits.
Dragonflies are usually larger with heavier bodies than damselflies. Dragonflies are also strong, fast fliers, whereas damselflies tend to flit about more daintily. Damselfly eyes are located on either side of the head, widely separated from each other. The eyes of dragonflies are extremely large and are positioned so close to each other that they almost touch. At rest, a dragonfly’s wings are held horizontally and perpendicular to the body, like the wings of a plane, while a damselfly folds its wings back along its long, slender abdomen.
There are about 6,500 species of dragonflies known worldwide, with more than 400 species found in North America. They are grouped into several families, with names like Skimmers, Darners and Clubtails. Members of the order Odonata are among the most ancient groups of insects, with the modern forms first appearing more than 240 million years ago. The predecessors of modern dragonflies and damselflies appeared more than 300 million years ago. One of these, Meganeura monyi, remains the largest flying insect known. Fossils of this giant dragonfly ancestor show it had a wingspan of 2 1/2 feet compared with modern species wing spans of just a few inches.
The dragonfly’s body is divided into three main parts: head, thorax and abdomen. The head is probably a dragonfly’s most notable feature, along with its two large, compound eyes, which are composed of thousands of individual units. These are supplemented by three smaller, simple eyes. As a result, most of the dragonfly’s brain is dedicated to processing visual information, and dragonflies depend exclusively on eyesight to detect their prey. Dragonflies also have a serrated and prehensile (adapted for grabbing) lower jaw used for seizing prey. Like all insects, dragonflies have antennae, but they are small and difficult to see on a live specimen.
The dragonfly’s six legs and two pairs of wings attach to its thorax. The thorax is the central part of the body. The wings are transparent and supported by a series of veins carrying a blood-like fluid called hemolymph. Dragonfly wings are strong and flexible and can flap independently of each other, permitting the insects to carry out such incredible aeronautic feats as taking off backwards or hovering.
The third part of the dragonfly body is the abdomen, which is flexible and can be curled around during mating. The abdomen is where the reproductive organs are located in both sexes, and on females, it is the location of the ovipositor, the organ used to deposit eggs.
The dragonfly life cycle has several distinctive features. Since male dragonflies maintain and defend a territory, a female that is ready to mate must first enter his territory. The male’s territory will be near a water body, such as a stream, river, pond or lake. Water is a critical aspect of dragonfly habitat, since the eggs and larvae must develop in an aquatic environment.
The male typically lands on a resting female and grasps her with his legs. They then take off with the male in the lead in what is called “tandem flight,” with the male holding onto the female with claspers located at the tip of his abdomen. When the two are ready to mate, they form a “copulation wheel,” in which the female bends her abdomen underneath her thorax and presses against the male’s body so that he can fertilize her eggs. After mating is complete, the insects separate and the female searches for a safe place to deposit the eggs. This will vary depending on the species of dragonfly and its habitat.
Females of some dragonfly species have an ovipositor with saw-like edges that are used to cut a slit into the stem or leaf of an aquatic plant, floating wood, or mud at the edge of a body of water. These species of dragonfly are called “endophytic,” meaning inside a plant. All other dragonfly females are “exophytic,” and have ovipositors that lack saw-like edges. These dragonflies deposit their eggs on the surface of the water or shoreline.
The length of time it takes dragonfly eggs to hatch depends on many factors, such as the species, the time of year and the climate. While most eggs hatch within a few weeks of deposition, the eggs of some dragonflies may overwinter and hatch the following spring. This seems to be more common in temperate areas, like North America and Europe. With many tropical species, the eggs remain dormant during the dry season and hatch at the beginning of the rainy season.
After hatching, the larval dragonfly emerges. These larval forms bear little resemblance to the adults, although both are voracious hunters. Larval dragonflies feed on a variety of aquatic organisms, including worms and other insect larvae and small minnows or baby fish fry. Dragonfly larvae come in two basic shapes, depending upon their habitat: bottom dwellers and weed dwellers. Bottom dwellers have flat bodies with short, strong legs that are used for digging into the mud. Weed dwellers, on the other hand, have long, streamlined bodies and actively hunt their prey among aquatic vegetation.
As the larval dragonfly develops, it goes through a series of molts, in which it sheds its outer skin, or exoskeleton. During this time, the body of the larva is soft and especially vulnerable to predators – including other dragonfly larvae. The larval stage lasts from a few months to several years, depending upon the species and environmental factors such as water temperature and food supply. After the dragonfly has completed its larval stage, it crawls from the water, usually onto the stem of a plant, and attaches itself to the stem with its legs. Here it will undergo metamorphosis and emerge from its larval body as an adult. Most dragonflies require a vertical surface for emergence, although some species can emerge on a flat surface, such as a rock.
Life on the wing
The adult dragonfly is designed for life on the wing, and nowhere is this more prominent than in its search for food. Dragonflies feed almost exclusively while flying, but they use different strategies to obtain their food. One of these strategies is called “hawking,” in which the dragonfly catches its prey in midair with its powerful jaws. The other method is called “gleaning.” This strategy involves the dragonfly hovering above a twig or leaf where a prey animal is perched, then swooping down to snatch the prey with its legs. Regardless of the strategy used, most dragonflies typically patrol back and forth across their hunting grounds, although some species will find a convenient perch from which to scan for prey.
Dragonflies are frequently seen in large swarms. These swarms may be migrations, similar to that of the Monarch butterfly. Sometimes, large groups of dragonflies may be concentrated in a narrow band of habitat, such as along a shoreline. One type of swarming behavior, called “hilltopping,” involves large numbers of dragonflies concentrated on open hilltops, usually away from the water. This behavior is believed to be related to mating, where numerous dragonflies concentrate in one area in hopes of finding a mate.
Dragonflies are fascinating creatures to watch, and you need not go far to see them. As with any wildlife species, dragonflies require food, water (lots of water) and a place for their young to develop. First, there should be some permanent source of water available, such as a stock pond, a stream or even a backyard water garden. Whatever your permanent source of water, it should have an abundant supply of emergent vegetation, aquatic plants that grow about the water, such as cattails, arrow root or water lilies. These provide habitat for prey, as well as perching sites for the dragonflies. Emergent vegetation is also important to provide a vertical surface for larvae to perch on as they make their final molt to become adults.
The bottom of the habitat should have plenty of “substrate,” materials that provide cover for both larval dragonflies and their prey. Leaves, branches and rocks are all good sources of substrate, as is submerged vegetation (the kind that grows under the surface of the water).
Of course, check with your agricultural extension agent before introducing any types of vegetation to a pond, lake or stream. Several exotic species are considered “invasive,” and introducing them to your water body may be illegal. These invasive species can take over a pond or lake in a relatively short period of time and choke out native species of both plants and animals. (Eurasian milfoil and water hyacinth are a couple that come to mind.)
Once you have attracted the dragonflies, you may want to identify their species. A number of excellent books and local field guides are available for dragonflies and damselflies, as well as websites for organizations dedicated to the study and conservation of the Odonata. Your local library, agricultural extension service office or university may also have information available on dragonflies. Happy dragon hunting!
Dragonfly Information Sources
Dragonflies of the World by Jill Silsby (Smithsonian Institution Press, Washington, D.C., 2001)
A Dazzle of Dragonflies by Forest L. Mitchell and James L. Lasswell. (Texas A &M University Press, College Station, Texas, 2005)
Wild Guide: Dragonflies by Cynthia Berger and Amelia Hansen. (Stackpole Books, Mechanicsburg, Pennsylvania, 2004)
Dragonfly Society of the Americas, Texas Natural Science Center, 1 University Station, #L7000, The University of Texas at Austin, Austin, TX 78712, www.OdonataCentral.org.
John Marshall teaches in North Little Rock, Arkansas, commuting from the small town of Benton, where he lives with his wife, children, granddaughter and several pets.