Article for July - August 2006
South Carolina’s Magic Dragons
by Austin Jenkins
photography by Jack Jenkins
From the perspective of a smaller insect, these “dragons” attack with biting jaws and catching claws, like creatures of fantasy . . . but they are real and living in our seemingly tame back yards.
Do you believe in dragons? If not, perhaps you should take a walk down by the water. There you will see that they do indeed exist. And yes, they are truly magical, much like Puff, flying in a wide variety of “painted wings and giant rings.”
What you’ll find, of course, are dragonflies. What an appropriate name for these ferocious creatures of the dark waters! Smaller insects likely live in constant fear of these tormenting aggressors. Certainly they should, for these predators are incredibly efficient, primarily because of their huge eyes and erratic, fighter-pilot flight. Perhaps they go unnoticed to many, but let us take a moment to explore the natural history of these fascinating animals.
What exactly is a dragonfly? How is it different from its cousin, the damselfly? Although dragonflies and damselflies are often called by the same name, differences exist between the fearless dragon and the damsel. Lynn Smith, president of the S.C. Association of Naturalists, explains: “When at rest, damselflies hold their wings together and above their backs, while dragonflies hold their wings horizontally, out to the sides.” Smith names size differences, too. Damselflies are small and slender compared to the larger dragonflies. Concerning structure, it is worth noting that dragonflies are some of the most primitive insects, first appearing in the fossil record 300 million years ago. Since then, there has been little need for change. Like their water-loving neighbor, the American alligator, dragonflies possess an efficient design that has rendered them timeless.
Dragonflies have an intriguing life cycle, which starts as an egg deposited beneath the water. Out of the egg pops a dragonfly nymph. This underwater larval stage can last from one to ten years, depending on the species and climate. Of course, underwater life requires oxygen, which the dragonfly nymph obtains from gills that exist within the rectum. So, the nymph practices what is often called rectal respiration—a pleasant thought. Aside from the aforementioned and the obvious, the rectum also serves as a means of jet propulsion—as water is quickly expelled, the insect is launched like a torpedo, escaping danger when the legs can’t move fast enough.
Nymphs exhibit the same ferocious feeding behavior as adults, and the diet consists almost exclusively of living prey. Dragonfly nymphs lack wings, so one would think that hunting would be a difficult task. However, prey capture is made keenly efficient because of a very unusual bottom lip, which moves out from the head like an upside-down backhoe, scooping up prey and bringing it into the waiting mandibles. Nymphs feed prolifically on mosquito larvae and other aquatic invertebrates.
At the inception of each growth stage (on average around twelve molts), the nymph sheds its skin, or exoskeleton, so that it can expand in size. Eventually, it begins to develop adult tissues. After climbing out of the water, the animal prepares for its final molt, an event called emergence. The exoskeletons often appear on trees and rocks surrounding the water.
“Life is short,” and the adult dragonfly knows this all too well, for its days are now numbered. Upon emergence, the adult dragonfly must buy some time for several reasons. Smith explains that newly emerged dragonflies are not quite mature enough to start breeding, and their exoskeletons have not hardened. They move away from the water, to areas where predators are less numerous and food is readily available. “At this point, they are a lot like teenagers, eating everything in sight. Once they have matured, they can then move back down to the water. Males will especially be found there, setting up territories and defending them with vigor. Females often stay in the uplands and move to the waters only when they are ready to mate,” Smith says.
Dragonfly mating is—well, weird but efficient. Talk about positions! In fact, odonatists (those who study dragonflies) have named dragonflies’ mating the “wheel position,” after the characteristic shape that is formed by the two mating animals. Odonatist Forrest Mitchell of Texas A&M explains that within the male, sperm is produced at the posterior end of the abdomen, or the tip of the tail as one may say. “Prior to mating, the male moves sperm from the end of his abdomen to an organ located just behind the legs. On the female, the organ that receives sperm is located at the end of her abdomen. For fertilization to occur, she must place this organ against the sperm-holding organ in the male, thus forming the wheel position,” says Dr. Mitchell. “She is able to hold this position because the male has tiny appendages on the end of his abdomen that grasp her behind the head as a means of support. These claspers enable the dragons to continue flying together during mating and afterwards,” he says. Why the complicated procedure? Mitchell answers, “the clasping behavior allows the male to prevent the female from additional matings. Many dragonfly males are able to remove sperm from the previous mate and replace it with their own. If the original male has the female captured while she is laying eggs, marauding males will not have the opportunity to displace his offspring.”
It would be “shortsighted” to omit a discussion of dragonfly eyes. Undoubtedly most important assets, dragonfly eyes allow them to detect color, ultraviolet light, polarized light and, most importantly, the movement of insect prey. In the insect world, large eyes such as these are called compound eyes, because they possess thousands of smaller eyes within. This does not mean that dragonflies see thousands of small objects if they are only looking at one. Rather, the image the dragonfly receives is a mosaic that depicts the single object of focus. The advantage: having a field of view that is almost 360 degrees all at once.
Dragonfly eyes also have high-speed perception that exceeds our imagination. Using baseball as an example, players with better high-speed perception are often the best hitters. The fast pitch is easier for them to observe. In the dragonfly world, prey that is flying in the opposite direction of a fast-moving dragonfly can still be captured, whereas we would only see a brief flash, if even that.
Other optical attributes include the detection of ultraviolet wavelengths, resulting in the sky’s appearing extra bright and creating better contrast between it and small insect prey. The detection of polarized light allows for twilight feeding. It’s easy to see that the dragonfly eye provides an important key to its success. However, for the dragonfly to take full advantage of the compound eyes, the animal must also have an equally effective means of propulsion.
Dragonflies are known as some of the fastest flying insects. Mitchell has clocked common green darners flying in excess of 20 mph. “However, their versatility in flight is even more developed than their speed,” he says. The dragonfly wing has an abundance of tiny cells, Mitchell explains, “and the specific arrangement of these cells allows the wing to change shape, depending on whether it is in the upstroke or down stroke. This changes its aerodynamic properties and allows the dragonfly to have powered flight on both the upstroke and down stroke. It also allows for the aerobatics and high-speed maneuvers for which they are known.” Working together, excellent eyesight and flight agility make the dragonfly a highly successful predator.
According to naturalist Rudy Mancke, “there are one hundred and ten dragonfly species currently known from our state. Considering that South Carolina is the smallest southeastern state, we have a great diversity of dragonfly species. This is because of the location of the state and the diversity of habitats within it,” he says. “We are at the edge of many of the northern ranges for dragonflies and the southern edge for others. Species are somewhat contained by the mountains to the west and the ocean to the east. This situation creates an exciting mix of species!” To add to this, Mancke says in recent years he has noticed that several Southern species are moving north into our state. Mancke says his favorite dragonfly is the Carolina saddlebags (Tramea carolina), which, like many other organisms, was named after our colony many years ago.
To hunt for dragons, start at a local pond or lake that contains ample vegetation. Excellent books for beginners include A Dazzle of Dragonflies by Forrest L. Mitchell and Dragonflies through Binoculars by Sidney W. Dunkle. Take the opportunity to marvel at these fantastic creatures, to go back in time to your childhood, when you did sit by the dark waters to watch and imagine and believe in dragons. The entertainment is free, the distance is close, the scenery is enchanting and the performance is altogether magical.
Austin Jenkins is a naturalist/graduate student at Clemson University working on a biodiversity survey at Clemson’s Sandhill Research and Education Center in Columbia.
© 2006 South Carolina Wildlife Magazine - www.scwildlife.com