Dragonflies and Damselflies: Odonata

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DRAGONFLIES AND DAMSELFLIES: Odonata

WANDERING GLIDER (Pantala flavescens): SPECIES ACCOUNTS
FOREST GIANT (Megaloprepus caerulatus): SPECIES ACCOUNTS

PHYSICAL CHARACTERISTICS

Odonates (OH-duh-nayts) have large eyes with ten thousand to thirty thousand individual lenses in each eye. The eyes of dragonflies meet, or almost meet, on the top of the head, while those of damselflies are widely separated, giving them a "barbell" look when viewed head on. The adults have four wings. The wingspans range from 0.8 to 6.5 inches (20.3 to 165 millimeters). Dragonfly wings are very strong and provide these insects with amazing flight maneuverability. The spiny legs are well developed for perching and seizing prey, animals that are hunted for food, but are of little or no use for walking. Instead, dragonflies rely on their four powerful wings for getting around. The large, strong wings are mostly transparent, see-through, and are supported by a network of veins. Some species have distinctly colored or patterned wings.

The ten-segmented abdomen of the dragonfly is long and slender. Males have a unique reproductive system with a special second set of structures on the underside, at the base of the abdomen. Damselfly and some dragonfly females have well-developed egg-laying structures for inserting their eggs into plant tissue. In most other dragonflies this structure is not very well developed, and their eggs are simply dropped into water. Both sexes have appendages (uh-PEN-dih-jehz), fingerlike structures, on the tips of their abdomens. The males use them like claspers to grab the female during mating.

Dragonfly larvae (LAR-vee) do not look like adults. Their bodies are thick and squat. They breathe with the aid of gills inside the abdomen. The bodies of damselflies are long and slender. Their abdomens are tipped with three leaflike gills used for breathing underwater. The long lower lips of all odonates are hinged at the base and extend forward like an arm. At the end of the lip are two jawlike structures armed with sharp teeth. Larvae capture their prey by thrusting the lower lip forward with blazing speed to grab them. When not in use, the lip is folded underneath the body, leaving the jawlike structures covering the face like a mask.

GEOGRAPHIC RANGE

Dragonflies are found worldwide, except in frozen polar areas. They are especially abundant in the tropics.

HABITAT

The larvae are found in most standing and running freshwater habitats, where they live on the bottom, under stones, clinging to vegetation, or buried in mud or detritus (dih-TRY-tuhs), loose, tiny bits of plant and animal remains. A few species live in small air pockets inside the stems of plants, while others occupy wet burrows in the ground in forests and marshy areas. Adults live near all bodies of freshwater, where they search for food, mates, and places to lay their eggs.

DIET

Larvae are ambush predators (PREH-duh-ters), meaning that they sit and wait for a food animal to come within their reach. Adults actively hunt and capture and eat insects on the wing, using their spiny legs as a basket for scooping up mosquitoes, gnats, midges, and other small airborne insects. The larvae capture insects, worms, and even small fish and tadpoles with their lower lips.

BEHAVIOR AND REPRODUCTION

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.

DRAGONFLIES AND DAMSELFLIES AND PEOPLE

Despite the menacing common names given to them, such as "devil's darning needles" or "horse stingers," odonates are harmless and are unable to sting. They eat large numbers of harmful insects, especially disease-carrying mosquitoes. Their presence or absence in bodies of freshwater is used as a measure of water quality. In fact, the Navaho Indians use dragonflies as a symbol to signify pure water.

Dragonflies are revered in East Asia, where they have been worshipped by people for centuries and used in medicines. Traditionally known as the "invincible insect," the dragonfly was a favorite symbol of strength among Japanese warriors. The ancient Chinese and Japanese used concoctions made from dragonflies or damselflies to treat a variety of illnesses, among them, eye diseases, sore throats, and fevers. Even the old name for the island of Japan, Akitsushima, means Island of the Dragonfly.

THE LARGEST DRAGONFLY EVER!

The largest wingspan for a living odonate belongs to an Australian dragonfly, Petalura ingentissima, measuring 6.5 inches (165.1 millimeters). The largest living damselfly, the forest giant (Megaloprepus caerulatus), has a wingspan measuring 6.4 inches (162.5 millimeters). The largest odonate in the United States is the giant darner (Anax walsinghami), from the American Southwest. Its wingspan is more than 3 inches (50 centimeters), and it has a body length of 4 inches (101.6 millimeters) or more. But the largest dragonfly that ever lived was Meganeuropsis permiana, an extinct species known only from fossils (FAH-suhls), ancient impressions of the insect's body left in mud that eventually turned to stone. It flew across the swamps of North America nearly 250 million years ago with wings measuring 28 inches (711.2 millimeters) across!

The Japanese have established more than twenty dragonfly sanctuaries across Japan. Images of dragonflies are found on tunnels, sidewalks, and city buildings of Nakamura City. The Yamma Bashi, or large dragonfly bridge, spanning the nearby Ikeda River, is supported by giant sculptures of dragonflies. Even the public transportation system pays tribute to these insects, with the Tosa Kuroshio Train, or Red Dragonfly, linking Nakamura City to Kubokawacho.

Large adult dragonflies are eaten by humans and are considered delicacies in many parts of the world. In Thailand they are roasted, mixed with shrimp, or eaten raw. In Indonesia odonates are mixed with other small animals in a thick, spicy soup. The Balinese fry dragonflies in coconut oil and serve them with vegetables. They also remove their wings and boil them in coconut milk seasoned with ginger, garlic, shallots, and chili pepper. Sometimes coconut meat is substituted for coconut milk, and the entire mixture is wrapped in a banana leaf and cooked together.

CONSERVATION STATUS

The World Conservation Union (IUCN) lists two species as Extinct, meaning that no member of either species is alive. Thirteen species are Critically Endangered, meaning that they face an extremely high risk of extinction in the wild in the near future, and fifty-five species are Endangered, meaning that they face a very high risk of extinction. Thirty-nine species are classed as Vulnerable, or facing a high risk of extinction, and seventeen are Near Threatened, or at risk of becoming threatened with extinction. For most species, very little is known about their distribution, or geographic range, and habitat preferences. Habitat destruction often prevents scientists from gathering important information that could help conserve species that are threatened by extinction. Programs to preserve dragonfly habitats are under way in Australia, India, Japan, Europe, South Africa, and the United States. Japanese conservation programs, which include the creation of artificial habitats to encourage dragonfly reproduction, are some of the best examples of efforts to conserve dragonflies and their habitats.

WANDERING GLIDER (Pantala flavescens): SPECIES ACCOUNTS

Physical characteristics: The body of the wandering glider is yellowish red in color. The base of the back wing is distinctly widened, with a faint yellowish patch. The abdomen narrows toward the tip and has a black strip along the back.

Geographic range: This species is found worldwide but is more common in the tropics.

Habitat: The wandering glider breeds in small, shallow pools, often in puddles left by thunderstorms. Adults are commonly found far away from water.

Diet: The species eats small flying insects, especially gnats, mosquitoes, and midges.

Behavior and reproduction: These insects are strong fliers and seldom land. They sometimes form large feeding and migratory swarms.

The feeding flights may continue into the early evening. They are often seen far out at sea and are attracted to the lights of ships at night.

Males patrol territories about 30 to 150 feet (9 to 45.7 meters) in length. After mating, the male remains with the female while she lays her eggs. Females lay their eggs by tapping the surface of the water with the tip of the abdomen. The larvae live in temporary pools, including swimming pools, and develop rapidly.

Wandering gliders and people: This species is not known to affect people or their activities.

Conservation status: This species is not threatened or endangered. ∎

FOREST GIANT (Megaloprepus caerulatus): SPECIES ACCOUNTS

Physical characteristics: This is the largest damselfly in the world, with a wingspan of 6.4 inches (162.6 millimeters) and a body length of 4 inches (101.6 millimeters). Their wings have a wide, dark blue band. The males are larger than the females and have a white patch before the blue band and the glassy wingtip. The females are shorter, with only white patches on their wingtips.

Geographic range: The forest giant lives in the rainforests of Central and South America, from Mexico to Bolivia.

Habitat: The larvae breed in water that collects at the bases of plants growing on the limbs of rainforest trees. Adults prefer sunlit gaps or clearings in the forest.

Diet: The adults are specialist hunters. They search for spiders and pluck them from their webs. Occasionally, they feed on the spider's own prey, which is wrapped in silk. The larvae feed on mosquito and fly larvae and small crustaceans (krus-TAY-shuns), animals that live in water and have soft, segmented bodies covered by a hard shell. They also eat tadpoles and the larvae of other species of damselflies.

Behavior and reproduction: Because their special breeding sites are scattered throughout the forest, these insects are never abundant at any given place or time. In an open forest gap, a territorial male uses a slow wing beat to appear as a pulsating, rhythmically beating, blue-and-white beacon to possible mates and to competing males. The male aggressively defends a particular tree hole for up to three months. After mating, the female uses her long abdomen to lay her eggs inside tree holes filled with water.

Forest giants and people: This species is not known to affect people or their activities.

Conservation status: This species is not endangered or threatened. ∎