Summer Dragons by Patricia and Raymond Heithaus was originally published in the BFEC newsletter, Vol. 13/No. 3, Summer 2009.
For a dragonfly, life begins in an egg that is dropped on the surface of the water, inserted into floating plants, or carefully placed in mud above the water line. Eggs laid into the water often begin development immediately while those deposited just above the waterline wait until the pond fills before beginning development. Eggs laid late in the season often enter a resting stage in which they wait through winter for an environmental cue, such as longer days, warmer water or rain to trigger growth. Most eggs hatch in a month and a larva emerges.
The larva has an external skeleton, which means that it will have to molt 10-15 times before it becomes an adult. Despite the promise of wings to come, the dragonfly larvae will spend almost its entire life under water.
True to their name, dragonfly larvae can breathe fire... Not really. But they are voracious predators for their size. Newly hatched larvae feed on microscopic organisms such as protozoans. As they grow, their diet switches to larger aquatic insects, tadpoles and small fish. Dragonfly larvae will eat anything that is the appropriate size and they use different strategies to capture prey. Some ambush their prey while others actively stalk them. Sit-and-wait predators hide in the mud or on aquatic vegetation as they wait for prey to wander by. They ambush prey by extending their labium (a long extension of the mouth) and piercing their victims with the spines protruding from the end of it. The victim is then drawn into the mouth and either crushed or swallowed whole. In species that specialize on small prey items, the labium is like a scoop with hairs that prevent prey from escaping. Dragonfly larvae are hard to keep in an aquarium because many species tend to be cannibalistic in addition to eating other residents. Good thing they’re measured in inches instead of feet...
Passing through the larval stage can take anywhere from several months to five years. For the final molt the larva leaves the pond crawling onto vegetation or rocks near the water’s edge. The exoskeleton of the larva splits along the back and the adult emerges. The larval exoskeleton (“exuviae”) is left attached to the stem and can often be found by careful observation of vegetation growing out of the water. The exoskeleton of the newly-emerged adult is soft and the wings are folded.
Young adults are entering a dangerous world. Their longevity is far from guaranteed. They are eaten by birds, frogs, fish, and even other dragonflies. With luck they will live long enough to rid our skies of mosquitoes, mate and continue the cycle of life. Some such as the Green Darner may even live long enough to fly south for the winter. Large swarms of Green Darners have been reported and scientists are just now starting to learn more about the migration of dragonflies.
Dragonflies are divided into exotic-sounding family groups with names that tend to set the imagination in motion. Forktails, petaltails, darners, clubtails, spiketails, cruisers, emeralds and skimmers aren’t extras from The Outsiders, they’re just a few of the dragonfly families that can be found in central Ohio. It doesn’t take too much imagination to think about how a clubtail might differ from a spiketail but how do darners and skimmers differ? The names might not be quite as clear but they do offer clues: the former are large, brightly colored high-fliers that can be seen darting and swooping over fields while the latter average about 1.5 inches in length and have clear or brightly patterned wings. Unlike darners, skimmers spend much of their time perched near ponds and lakes.
Skimmers and other dragonflies differ from their small cousins the damselflies in that they cannot fold their wings over their backs. When they land their wings are extended out to the side. This exposes the entire wing surface to the sun and provides an efficient way for them to warm their flight muscles.
Dragonfly activity is highly dependent on the weather. Most species become active as the sun comes out and the temperature rises. A visit to the ponds early in the morning can often provide opportunities to view dragonflies before they take to the sky. Some species become more active at dusk when potential prey like mayflies emerge. In the fall, large aggregations of darners and saddlebags can be seen cruising back and forth across the wetland. They are feeding on small insects such as mosquitoes, so give them a “huzzah!” if you happen to be passing by.
Dragonflies have good eyesight and are able to recognize members of their own species. They use such characteristics as wing pattern, body markings, eye color and the size and structure of abdominal appendages.
In many species the male and females have distinct color patterns. Courting males tend to defend a small territory by chasing other males away. Depending on the species, territories are defended by the resident flying up from a perch or patrolling constantly on wing.
With luck you will be able to see reproductive behavior. Various techniques of mating are used. In some species mating takes only seconds while for others like the green-eyed prince baskettail mating can last for over 20 minutes. The male baskettail patrols the pond until a potential mate appears. He uses his abdominal appendages to grasp the female just behind the head and she rolls her body so that together they form a circle (or “wheel position”). In this position the female can remove the sperm from an accessory organ near the base of the male’s abdomen. The pair may continue to fly in wheel position or land. The mating behavior of the large green darner, common at the BFEC, differs slightly. After briefly flying in a wheel position the female uncurls her abdomen. The male continues to hold the female and the pair fly in tandem until they land on floating vegetation. The male supports the female while she makes a slit in the stem and lays her eggs. The male stays with her until all the eggs have been laid. In other species, the male does not assist during the egg laying.
After mating, the male leaves the female to deposit eggs while he patrols the sky overhead, chasing other potential mates away to assure that the offspring are his. Other species invest far less; males simply mate and fly away.
Dragonflies have been on the Earth for 325 million years — older than the first dinosaurs! Even so, many species now face conservation challenges. Their need to first grow in aquatic habitats makes dragonflies sensitive to a host of potential ills: water pollution, loss of wetlands, sedimentation or alteration of streams, clearing of pond and lake shores and drought. Also, adults of different species each require particular places to hunt and find mates: river corridors, grasslands, meadows or woods are essential and all-too-often wind up in the habitat-lost column. By ensuring that many types of aquatic and terrestrial habitat are protected, the BFEC is helping to conserve this ancient line of animals.
The next time you visit the BFEC keep an eye out for our soaring dragons. To learn more about the kinds of dragonflies commonly seen at the BFEC, visit our website. Even better, explore the BFEC and Knox County in person!