Flying dragons like a flash of light

The dragonflies of the insect world fully live up to their name not only as aerial acrobatic adults but also as youthful, aquatic nymphs (naiads). The adult darts about with amazing speed and agility—like a flash of light—as it leaves its perch to capture a helpless fly or mosquito on the wing. The wings of the dragonfly are large and gauzy and are always held in a horizontal position, never folded, as with many other winged insects. The eyes are composed of from 10,000 to 30,000 individual facets or lenses giving this insect a keener, mosaic vision than that of other animals in his habitat. Dragon and damselflies make up the insect order Odonata. The scientific name refers to the teeth on the lower jaw or labium of the immature nymph. There are some 407 species of Odonata in America north of Mexico and about 4,870 known species worldwide. As one watches these aesthetically pleasing insects maneuver about the countryside, it seems absurd that there are so many incorrect folktales about them. My grandmother always referred to a dragonfly, as a “Devil’s Darning Needle,” and she halfway believed the insect would sew shut the ears of anyone who listened to gossip about another person. Some individuals call them “Snake Doctors” and are sure they can restore life to a dead snake. In some parts of the country, it is held as gospel that a dragonfly landing on one’s fishing line or float is a sure indication a fish will bite soon. Despite all of this slander and folklore, the dragonfly remains not only harmless to man, but, in reality, is his friend and ally in waging war against pestiferous and dangerous mosquitoes and flies. Dragonflies are especially valuable in the natural control of mosquitoes. The aquatic nymphs devour great numbers of mosquito wrigglers and the voracious adults devour any adult mosquito so foolish as to wander into their flight path. The nymphs of dragonflies differ anatomically from their parents in almost every respect. They are found in ponds and lakes and are sluggish as they slowly wander about on the bottom of the impoundment. They obtain oxygen via a set of gills located in the rectum and, by muscular contraction, water is moved gently in and out of the lower digestive tract. On occasion, water may be forcibly ejected giving the nymph a sort of jet propulsion to escape an enemy or catch a prey animal. The nymph will usually lie motionless on the bottom waiting for a small animal to come within range. Then, with the speed of a striking rattlesnake, the long, folded lower lip is shot forth, and the victim is impaled on the hook-like teeth on the tip. The victim is drawn into the mouth, where the sharp jaws quickly cut it to bits. Some years ago a biologist asked the question, “How many mosquito wrigglers does it take to make a dragonfly?” To answer this puzzler, he attacked the problem directly by setting up an aquarium containing a single dragonfly nymph. He then proceeded to feed the nymph as many mosquito larvae as it would accept in a 24-hour period. At the end of a year’s time, he calculated the dragonfly had devoured a total of 28,440 mosquitoes. Depending on the species, a dragonfly nymph’s development may require two or more years. Sometimes we wonder if the uses of chemicals applied to bodies of water for the control of mosquito larvae defeat the purpose by killing dragonfly nymphs and other mosquito predators along with the target organisms. Some years ago I conducted tests at my university in Maryland and concluded that the concentration of insecticide in wide use at that time for the control of larval mosquitoes was also lethal to dragonfly nymphs and other aquatic forms. Maybe it would be best to use chemicals only in case of emergencies, such as an epidemic of mosquito-borne disease, and let natural populations regulate themselves. These fascinating insects have received lavish attention from writers in the past. The Hoosier Poet, James Whitcomb Riley, paid them a delightful tribute when he wrote: “Till the dragonfly, in light gauzy armor burnished bright, Came tilting down the waters in a wild, bewildered flight.” Dr. Robert Hedeen is a former resident of Maryland’s eastern shore and resided in the Chicago area from 1960-1971. He is a retired professor emeritus of biological sciences in the University of Maryland system. He has published more than 30 scientific papers, has written numerous magazine articles, and is the author of two books on the natural history of the Chesapeake Bay.

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