Coastal Wildlife & Native Plants
By John Marshall
Dragon Flies: Aerial Acrobats
Here on the Gulf Coast we have a great diversity on insects. Some are pests, most are harmless and some are actually beneficial. Among the last group are some of nature’s greatest aerial acrobats, the dragonflies. Their aerial movements are the envy of human pilots and aeronautical engineers; their ability to catch flying insect pests on the wing, nothing short of amazing.
Dragonflies, and their smaller cousins the damselflies, belong to the insect order Odonata. Dragonflies are usually larger with heavier bodies than damselflies and are strong, fast fliers. At rest, dragonfly wings are held horizontally and perpendicular to the body, while damselfly wings are folded back along the body.
The dragonfly’s body is divided into three parts: head, thorax and abdomen. The head is the dragonfly’s most notable feature, along with its large compound eyes. The eyes are composed of thousands of individual units and are supplemented by three smaller simple eyes. Most of the dragonfly’s brains is dedicated to processing visual information and they depend exclusively on eyesight to detect their prey. Another feature of the head are the serrated and prehensile jaws used for seizing prey. Like all insects, they have antennae, but they are small and hard to see on live specimens.
Dragonflies have six legs and two pairs of wings attached to the middle of the body, the thorax. 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, allowing them to hover or fly backwards.
The third part of the dragonfly’s body is the abdomen, which is flexible and can be curled around another dragonfly during mating. The abdomen is where the reproductive organs are located in both sexes. On females, it is the location of the ovipositor, the organ used to deposit eggs.
Adult dragonflies are designed for life on the wing, especially when it comes to searching for food. Some dragonflies hover above a twig or leaf where the prey is perched and swoop down to snatch it up with its legs. At other times, they catch flying prey right out of the air.
Dragonflies are frequently seen in large swarms that may be migrations. Sometimes, large groups concentrate in a narrow band of habitat, such as the shoreline of a lake or stream. “Hilltopping”is another form of swarming in which large numbers of dragonflies concentrate on hilltops. This behavior is believed to be related to mating.
Dragonflies have a complex life cycle. Tales defend a territory, females ready to mate must first enter that male’s territory. This is near a stream, pond or other water body. Freshwater is a critical part of the dragonfly habitat, since the eggs and larvae must develop in an aquatic environment.
During mating, the male grasps the female with his legs and they take off together, mating on the wing. After mating, the female searches for a safe place to deposit her eggs.
Females of some dragonfly species have an ovipositor with saw-like edges that is used to cut a slit into a stem or leaf of an aquatic plant, floating wood or mud at the edge of a body of water. Other species lack the serrated ovipositor and simply deposit their eggs on the surface of the water or on the shoreline. The length of time it takes the eggs to hatch varies with species, time of year and climate, but most dragonfly eggs hatch within a few weeks in North America.
After hatching, the larval forms emerge. These bear little resemblance to the adult form. Larval dragonflies feed on other aquatic insects, worms and even small fish. The larvae come in two basic forms: bottom dwellers and weed dwellers. Bottom dwellers have flat bodies with strong short legs for digging in the mud. Weed dwellers have long streamlined bodies and actively hunt prey among aquatic vegetation.
As the larval dragonfly develops, it molts its exoskeleton, or outer skin, several times. The larval stage lasts from a few months to several years, depending on the species, water temperatures, and food supply. After the larval stage is complete, the dragonfly crawls from the water onto a stem of leaf, attach itself with its legs and go through its final molt, emerging as a winged adult.