This is the Garden Column for the week of May 12, 2006.
By Donald R. Lewis,
Iowa State University
Who isn’t familiar with dragonflies, one of the most charming insects of summer? The graceful flight of dragonflies along a lake, stream or pond is one of summer’s best shows and the bright colors of the long, slender body and the sparkling cellophane transparency of the wings make them a favorite of jewelry makers and artists.
Dragonflies also are a favorite for insect collections but collectors are more often than not frustrated because dragonflies can be as hard to catch as they are beautiful.
Several nicknames and myths surround these insects. The nickname “devil’s darning needle” has been applied to some of the larger species who are alleged to stitch shut the eyes or ears of children as they sleep. The nickname “horse stinger” is without merit since these harmless insects can not sting or bite. The nickname “mosquito hawk,” however, is accurate as the dragonflies consume large quantities of mosquitoes and other small flying insects during their tireless flights.
Dragons and Damsels
Dragonflies are accompanied in the airspace near water by their close relatives called damselflies. The two groups have many similarities such as long slender bodies, elongate, membranous wings with a crowded network of veins and large heads composed almost entirely of multifaceted, compound eyes, but they are easily distinguished from each other. Damselflies are smaller and more delicate looking than dragonflies and when damselflies rest, they hold their wings straight up and together above the body. Dragonflies, on the other hand, rest with their wings held horizontally.
If these insects appear somewhat primitive, it’s because they are. Dragonflies have remained unchanged, with one possible exception, for over 250 million years, according to fossil records. While our largest dragonflies are about 3 inches in length with wingspans of up to 7 inches, some early dragonflies had a wingspread of 27 inches. Dragonflies evolved long before the time of the dinosaurs and may have been the first insects and even the first animals to fly.
Life in the Water
Dragonflies and damselflies are aquatic insects that spend most of their life in the water. Unlike butterflies and beetles, dragonflies and damselflies have a simple life cycle of three stages –– egg, nymph and adult. The adults lay eggs on or near the water. The eggs hatch after three to five weeks into nymphs called naiads. The naiads live more or less buried in the mud or attached to submerged plants for several months or up to as long as three years.
Naiads only vaguely resemble the appearance of the adults. Naiads have the long slender body, six legs and large heads, but without wings they may be difficult to recognize. A noticeable feature of the naiads is the large, well–developed mouthparts hinged to the lower side of the head. Nymphs feed on small aquatic animals such as insects, worms, tadpoles and even small fish by lying in wait and snatching prey as it swims or crawls by. The elongated lower lip shoots out and snares the prey with two movable claw-like hooks. When the lip is withdrawn the captured morsel is chewed up in mandibles at the base of the lip.
When the naiads are fully grown they crawl out of the water on the stem of an aquatic plant. The adult emerges from the naiad skin and begins the half–hour long process of expanding the wings to their full size before flying off to find a mate. Adult dragonflies and damselflies are aggressive predators. Adults flying back and forth over the water or darting in a zig–zag fashion above your lawn are literally scooping mosquitoes, gnats, winged ants and other small insects from the air using their spiny front legs that are held like a basket just under the mouth.
On the average, an adult dragonfly may live up to six weeks while damselflies have an adult life of three or four weeks. During that span, mating, a commonly observed behavior of dragonflies and damselflies, must occur before the female can lay fertile eggs to start the life cycle over.
Most dragonflies and many damselflies mate on the wing, spending considerable time flying “in tandem.” The male clasps the female by the back of her head using special appendages at the end of his abdomen. Prior to clasping the female the male transfers a packet of sperm from the tip of his abdomen to a storage sack on the bottom of the abdomen just behind the legs. The actual act of copulation occurs when the female bends her body forward and connects to the underside of the male’s abdomen for purpose of transferring the sperm. Some dragonflies and damselflies remain in this position for several days to ensure successful fertilization.
Dragonflies and damselflies do no harm to people, pets, crops, landscape plants or houses. They are entirely beneficial, first as a vital part of the aquatic food chain, and second as predators of mosquitoes and other pests. Live and let live. Sit back and enjoy the show.