Dragonflies and Damselflies: Odonata

Dragonflies always perch with their wings flat and spread apart, while damselflies usually hold their wings together over the body when they are at rest. The exceptions to this rule are the damselflies known as spreadwings, which keep their wings angled away from their bodies at rest.

Dragonflies regulate body temperature by assuming different postures, ways of holding their bodies, and selecting specific perching sites. In cool weather they create a whir with their wings and land on sun-facing perches. In hot weather they avoid overheating by sticking the abdomen almost straight up in the air to expose the least possible body surface area to the hot sun.

Dragonflies are among the world's most agile (A-juhl), nimble, flying animals. Some species have been clocked at speeds up to 35 miles (56.3 kilometers) per hour. They can hover effortlessly or fly short distances backward. Their bristly antennae (an-TEH-nee) and wing hairs track changes in wind speed and direction. The U.S. Navy and Air Force have studied their aerial acrobatics and learned that dragonflies twist their wings on the downward stroke, creating miniature whirlwinds to reduce the air pressure above the wing, so that they remain in the air.

Many males are territorial, meaning that they protect their living areas. They patrol their areas of water, chasing away all other males. In some species, males make threatening displays for other males or courtship displays for females, by exposing color patches on the head, legs, abdomen, or wings. Females cruise through these territories in search of possible egg-laying sites.

Mating in dragonflies and damselflies is unique among all animals. Before mating, the male bends the abdomen forward underneath his body to transfer sperm from the tip of his abdomen to a second set of reproductive structures, near the base of the abdomen. When he finds a mate, he uses the appendages at the end of his abdomen to grasp the female. Dragonfly males hold the female at the back of the head, while damselflies grab the front part of the thorax, or midsection of the body. The female responds by bending her abdomen forward to bring her reproductive structures in contact with those of the male near the base of his abdomen. Coupled together in this position, males and females resemble a wheel. After mating, the female lays her eggs by herself or is guarded by the male, who continues to hold her. She lays her eggs in the water, either simply dropping them off or placing them in mud or plant tissues.

The larvae, which lack wings, develop in the water. Depending on water temperatures and food supplies, they take six months to five years to reach adulthood and will molt, shed their external skeleton, several times. Mature larvae leave the water at night to avoid predators and to molt for the last time. They crawl onshore and climb up nearby plants, rocks, or tree trunks. The external skeleton splits open along the back of the thorax. This opening forms an escape hatch through which the newly formed adult can leave its old body. The new adult is pale and soft at first, and its wings are crumpled. It hangs upside down until the abdomen is completely withdrawn from the old larval skin. The new adult then turns around and hangs head upward until the wings have fully expanded and stiffened. By morning it is ready to take its first flight. After reaching adulthood, some species will undertake long-distance migrations (my-GRAY-shuns), sometimes flying hundreds or thousands of miles. Adults live one to two months in cooler climates, but some tropical species may live for a year.