Wikijunior:Bugs/Dragonfly
What does it look like?
editDragonflies are large, slender insects that are up to 5 inches long. Dragonfly colors are brilliant blue, green, or brown. Compound eyes are large and hemisphere-shaped. Each compound eye has up to 28,000 separate lenses (ommatidia). The thorax is just behind the head and is the power center. Its strong muscles control the two pairs of wings.
Dragonflies belong to the Order Odonata. They have wings that extend horizontally to the side. They are unable to fold their wings flat against the body. Some smaller species are less than 1 inch long. Dragonfly legs are not made for walking. They bend, but are not very flexible. They have claws on the ends for grasping prey in flight and perching on leaves and twigs.
Darners are large and fast-flying dragonflies belonging to the family Aeschnidae. They are 2-3/4 to 4-3/4 inches long. They have large, clear wings with a span as wide as 5-7/8 inches. Darner naiads are 2 to 2-1/2 inches long with relatively short legs. Their flat lower lip lacks grasping bristles.
Green Darners are dark greenish-brown with green thorax. The abdomen is blue to purplish-gray. The pale wings have light yellow tips. Green Darners have a target-like mark on the face. Naiads can be as long as 1-7/8 inches.
Brown Darners have brown bodies and 2 large, pale yellow spots on each side of the thorax. There is a brown spot at the base of each wing and a yellowish spot on the front wing margin.
Biddies are brownish-black with yellow markings. Most have a very long abdomen. Their heads are wide with eyes that are slightly separated or meet at a single point. Antennas have 7 segments. Biddies are large and hairy with wings that are clear or smoky. Wings have a black spot (stigma) along the front margin. Naiads are stout and hairy with huge spoon-shaped lower lips.
Green-eyed skimmers belong to the Family Corduliidae. They are often quite hairy. Many are brownish-black in color with a red, green, or blue metallic sheen. The abdomen is metallic green and may be long and cylindrical or flat. On the head, eyes touch each other. The thorax is hairy and wings have yellow marks.
“Downy Emerald” dragonflies (Cordelia aenea) are named for their hairy bodies and green abdomens. Their wingspan can be up to 2 inches.
Small Western Gomphids are about 2 inches long and have a 4-inch wingspan. They have a yellowish face and a thorax that is black with yellow markings. The abdomen is black with a yellow tip and base. On the abdomen, there is a thick yellow stripe that narrows to a thin line. The wings are clear. The naiads are dark brown in color and about 1 inch long.
Club-tailed dragonflies have brightly colored bodies. The thorax is yellowish with dark markings. The body has various patterns and color combinations of black, yellow, or green. In males, the end of the abdomen is swollen, giving the appearance of a club. Females sometimes have this feature as well.
Common skimmers or “darters” usually have stout, colorful bodies and a broad, flat abdomen. Wings sometimes have dark, irregular markings with a dark base next to the body. The thorax has pale stripes on either side. Male abdomens are pale blue and females’ are brownish yellow. Both sexes have yellow marks at the side of the abdomen. Nymphs are often short and slightly flat.
Where does it live?
editBrown Darners are found from Nova Scotia to Florida, west to Texas, and north to Illinois. They live at the edges of free-flowing streams. They are good fliers but do not fly very far from their home stream. Brown Darner naiads are found under stones and debris near woodland streams. Green Darners live near ponds and slow streams throughout North America. They are less common in the west. Walsingham’s Darners live in the Southwest and Heroic Darners are found from Mexico to Quebec.
Gomphids live near streams. They can be found resting on logs, stones, and leaves or darting one resting place to another. Sometimes they fly along roads or through woods far from the streams. They return for mating and laying eggs.
Small Western Gomphids are found near small rippling streams from Nevada to Baja California and north to British Columbia.
Biddie naiads live in forest streams and cover themselves with silt. Adults can be seen flying slowly up and down streams, hovering about a foot above the water.
What does it eat?
editDragonflies eat a wide variety of insects. Their prey includes flies butterflies, and mosquitoes. They have been known to eat hummingbirds. They are specialized hunters with large freely moving heads, large compound eyes, and sharp biting mouthparts.
Green and Brown Darners and Small Western Gomphids eat small flying insects like caddisflies and mosquitoes. Club-tailed dragonflies eat small flies, midges and mosquitoes. They use their specially shaped legs to scoop up prey while in flight. Catching insects while in flight is called “hawking.” Hovering over plant life to catch insects is called “gleaning.”
Dragonfly nymphs eat water fleas, worms, and insect eggs. As they grow they feed on bigger prey like water beetles and snails.
How does it defend itself?
editWith a large head and large compound eyes they can see predators more easily. The multiple lenses in a dragonfly’s eyes allow them to easily see motion and color.
Catching dragonflies is not easy. They seem to fly in 2 different directions at once. Their ability to move swiftly through the air, darting and weaving lets them avoid predators. When the four powerful wings move independently, they are able to fly both forward and backward.
Many species are mottled with different colors that act as camouflage in wooded areas near ponds and streams.
Dragonfly nymphs bury themselves in silt, mud, or gravel. Just the head and front legs are left out to grab prey. They are hidden from predators.
What stages of metamorphosis does it go through?
editDragonflies undergo simple metamorphosis with three stages—egg, nymph, and adult. Naiads crawl out of water when fully grown. Males mate right away because they only live between one day to several weeks. Females live longer so they can lay eggs. Typically 500 to 1500 eggs are deposited. They hatch in 5 to 60 days depending on location and temperature. Very few eggs survive to adulthood.
Mated pairs of Brown Darners can be seen resting on lily pads while the female deposits her eggs into the water. Naiads turn into adults in May in the north and October in the south.
Female Gomphids lack ovipositors. To lay eggs, females break the water surface with the tip of the abdomen and deposits eggs while in flight. Biddies lay eggs on the bottom of rivers and in fast-flowing streams.
Green-eyed skimmer females can lay more than 2000 eggs at a time. Nymphs usually live at the bottom of stagnant water in marshes or peat bogs.
Club-tailed Dragonflies mate in vegetation. Females hit the tail on the surface of shallow water to release eggs. The larval stage lasts from 3 to 5 years. Discarded larvae cases are short and squat instead of long and slender like other dragonfly larvae cases.
Most males are highly territorial. They choose an area that has a good egg laying site. They protect the area by dive bombing any other males and forcing them away.
What special behavior does it exhibit?
editGreen Darners form a “mating wheel” shape while attached upside-down to each other. After mating, the male tows the female around over water to deposit eggs in water plant stems. This tandem flight behavior is called “contact guarding.” It allows the male to protect the female from efforts of other males to mate with her.
Most dragonfly species have a resident population, but some have a migrating population. Migrating populations travel by day following the same migration paths as song birds and hawks. They can make corrections if they go off course. They stop to rest every 3 days. Some can cover as much as 100 miles per day. Nymphs of migrating species hatch and develop faster than those of resident species.
Dragonflies sometimes swarm together on the top of a hill far from water. This behavior, called “hilltopping,” may be for finding mates.
How does this bug affect people?
editDragonfly naiads and adults are beneficial because they destroy huge numbers of mosquitoes. In Thailand, they are used as pest control to keep mosquitoes and other insects away from rice paddies.
Dragonflies have a place in folklore of many countries. They are said to sew together fingers of sleeping people and lips of gossips. In the Middle Ages they were called “devil’s needles.”
In the United States they have different names—mosquito hawks, darning needles, snake doctors, and snake feeders. In Japan, they are a sign of good luck, courage, and strength. Inside the home, they are thought to be a visiting spirit. They are a part of Native American art and creation myths.
Dragonflies are used as an “indicator” species to determine if a pond or other body of water is healthy. They play an important role in preserving the balance of nature. In Italy they are called “keepers of the fish.”
References
editLockwood, S. (2008). Dragonflies. Mankato, MN: The child’s world.
McGavin, G. C. (2000). Insects spiders and other terrestrial arthropods. New York, NY: Dorling Kindersley, Inc.
Milne, L. & Milne, M. (2009). National Audubon Society Field Guide to North American Insects and Spiders. New York, NY: Alfred A Knopf.
http://www.cirrusimage.com/dragonfly_green_darner.htm