The order Odonata, in which the dragonflies and damselflies are placed, is derived from the Greek word meaning “toothed.” Dragonfly mouthparts have strong mandibles that are used to chew prey. The body of dragonflies is well adapted for hunting and capturing insects.
Adult Body Plan
Their eyes sometimes almost completely cover both sides of the head – making the head resemble a football player with his helmet on, or at least cover more than half of each side of the head and they may even be larger than the head itself.
The body is designed for rapid aerodynamic flight with a deep, muscular thorax and long, thin abdomen. The four wings can move independently of each other and allow the insect to turn rapidly or even stop almost instantaneously in mid air. They can also fly backward and sideways.
The six legs are not used for walking, but are necessary for perching and stiff hairs on the legs form a basket to swoop up insects in mid air. The image of the Clamp-tipped Emerald female shows this basket.
Mating Behavior
Once mature, a male dragonfly or damselfly establishes a territory from which he chases other males. When on territory, he produces packets of sperm called spermatophores at the tip of his abdomen (tenth segment), reaches the tip forward and places the spermatophores in a depression on the lower surface of the second abdominal segment.
With his sperm receptacle filled, the male flies out and grasps a female's head with his clasping genitalia at the abdominal tip. Each species' male genitalia fit the head of only the female of that species. (Slaty Skimmer Clamped in Tandem.) In some dragonflies and damselflies, the shape of the male genitalia is the most constant and accurate identifier of the insect's species.
Once the male has grasped a female, they fly in tandem for some time (Swamp Spreadwing in Tandem). The male usually flies while the female rests. Rarely, the female will fly while the male rests. It is unusual for both odonates to be flying at the same time.After some time, the female reaches the tip of her abdomen below her body and grasps the male's second segment to pick up the spermatophores he placed there. During this process, called the wheel formation, the two dragonflies take on a circular or heart-shaped pose. The two may stay in the wheel formation for upwards of fifteen minutes before the female releases and returns to the tandem position. (Eastern Forktails in Wheel Formation image.)
Egg Laying
Once the wheel is broken, the female may leave the male, separate from him as he remains close to her, or they may stay together in tandem as she goes about laying eggs (oviposition). Oviposition may take many forms:
- Skimmer females usually leave their mates soon after breakup and fly over shallow water, dropping to the water's surface to lay her eggs and rising again.
- Darner males do not release their females and carry them to likely places for oviposition. The female dips her abdomen to the water's surface and they rise a couple of inches before flying to a new location.
- Some damselfly males do not release their mates – even when the female climbs down a plant stem to lay her eggs in that stem, but several centimeters below the water's surface. The male may be dragged down until he is almost submerged, but he is needed to help her break through the water surface once egg laying is over.
- Emerald dragonfly females have thorn-like ovipositors with which they stab the mud surrounding the bogs in which they lay their eggs. (Red and yellow arrows in the photo of the Clamp-tipped Emerald.) The eggs are deposited below the surface of the mud to hatch when rains raise the level of the bog and submerge the mud.
- Some damselflies and dragonflies, including the two primitive Anisotrophomorpha species, lay their eggs in the stems and leaves of sedges, rushes, and aquatic plants. Many that use aquatic plants have saw-like ovipositors that slice through the outer tissues of these structures and allow the eggs to be inserted below the stem surface. (Red arrow in the Eastern Forktail Female picture.) There have been several studies on ovipositioning scars on fossil leaves and stems from the Carboniferous Period, and many of these scars have been attributed to dragonflies and damselflies.
Dragonflies are unique in the insect world in their morphology and behaviors. Being predatory, they are important in keeping the numbers of pest insects in check. Their ability to dart here and there, check their flight in mid beat, and turn to capture insects is unparalleled in the animal kingdom. Yet, there are parasites that sap their strength, predators that catch and eat them, and they are subject to injury from inclement weather and storms. Aquatic life of nymphs is described on page one.
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