by Andrea Laine
This summer my Durham garden has been graced by two large blue dragonflies with wingspans of almost three inches. I do not recall ever noticing a lingering presence of dragonflies anywhere else I have gardened. So I was struck with delight when one day’s sighting led to another and another and another.
I’ve enjoyed watching them for weeks now. From my second-story home-office window I see them zoom around in circles and spirals like vintage planes at an air show. They are fast and yet delicate. Sometimes they fly in unison, which is especially eye-catching when rays of sun make their lacy wings seem to sparkle. Other times they fly solo, zig-zagging from one garden spot to another, from one perch to another. Pointy objects seem to be their favorite perches: the tip of the orange beak of a larger-than-life blue heron sculpture that marks the entry to my front walkway; or atop the silver metal antenna of the 1990 Toyota parked in the driveway.
Today as I paused waiting for my watering can to fill, one swooped over and hovered before me at (my) eye level as if to say hello. Or at least, let us formally acknowledge one another’s existence. No longer could I just be mesmerized by their daily dance; My curiosity was piqued. I had to learn more about this unique and colorful creature.
Dragonflies belong to the scientific order Odonata, meaning “toothed ones,” and the suborder Anisoptera, meaning “different wings.” Their hindwings are distinctly larger and differently shaped than their forewings. There are hundreds of dragonfly varieties in the United States. The anatomy of wings and their venation can be very complicated. Most dragonflies can be identified to the level of genus and many to the level of species by just knowing the wing venation.
I have sunny, hot days to thank for a dragonfly’s presence. Many dragonflies maintain an internal temperature as high as 110 degrees F. This is accomplished by the burning of calories during physical exertion and by staying in the sun. A cold dragonfly preparing to get the day started will shiver its wings to create heat in its thorax until it has warmed itself enough to take flight. On cool or cloudy days, dragonflies will disappear to protected perches.
Dragonflies live to eat and mate. They are formidable and efficient hunters aided by excellent eyesight, resilient and maneuverable wings, spiky legs that can snag live prey, and a powerful thorax serving both the wings and the legs. Their prey includes mosquitoes, moths, beetles, butterflies and damselflies.
Dragonflies have no sense of hearing, cannot smell and are unable to vocalize. Their antennae are tactile sensors, picking up even slight movement. Antennae also help dragonflies measure wind direction and wind speed. They can fly up to 35 mph and they mate while flying in the air.
To drink, a dragonfly will thrust its body onto the water’s surface and absorb water through its exoskeleton. I haven’t witnessed my visitors doing this, but perhaps they are making use of a couple of 12-inch saucers I leave in the garden to collect with rainwater for thirsty beneficial insects like bees.
Dragonflies undergo three stages of development: the egg, the larva (nymph) and the adult.
The eggs are laid underwater in plants in ponds or marshy areas. When a nymph is ready to mature to the adult stage, which could be one to three years after hatching, it sheds its larval skin and crawls up a plant stem, a rock, a tree trunk or a dock to exit the water.
The adult dragonfly tends to emerge from the water very early in the morning to protect itself from predators, particularly birds. The mortality rate at this juncture can be very high. And, as adults they live just a couple of months. Knowing that makes me appreciate even more that this particular pair of dragonflies chose to live in my garden this summer.
More about the biology and behavior of the dragonfly: http://mndragonfly.org/defined.html.
Photos of dragonflies: http://www.carolinanature.com/odonata/ (a link recommended by ces.ncsu.edu)
The Book of Dragonflies of the East, a fully illustrated guide to all 336 dragonfly and damselfly species of eastern North America http://press.princeton.edu/titles/9538.html