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Field Notes-Rich In Dragonflies



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Field Notes—

Rich In Dragonflies

By Curtiss Clark

On any given summer day, jeweled airborne needles relentlessly stitch up sunny afternoons in our yard.

Because we live within a quarter mile of four ponds, a woodland stream, and their boggy surrounds, we are rich in dragonflies. They arrive in June and spend the entire summer conducting aerial raids on smaller insects, and sometimes each other, before they mate, lay eggs, and die in the foreshadows of fall.

For sheer beauty, they can outshine the birds. They arrive on vaporous wings in the multicolored wardrobes of royalty — vermilion, emerald, indigo, yellow, orange, white, and black — and they have the habit of perching on precisely the single sunny spot that shows them to their best advantage. They are gems on the wing — something that has not escaped the notice of jewelers who seem never to tire of trying to capture their beauty in gold, silver, and precious stones. Tiffany & Co. currently offers a line of dragonfly jewelry including a bracelet in gold, freshwater pearls, and diamonds that sells for $9,750. The diaphanous insects that have inspired these expensive re-creations, however, are truly ancient treasures.

Dragonfly impressions have turned up in fossils more than 300 million years old. They took wing 150 million years before the birds and predate the dinosaurs by more than 100 million years. They were here when the Appalachian mountain range was pushed up by the collision of land masses that eventually sorted themselves out as North America, Europe, South America, and Africa. These little winged needles tug at some of the longest threads in creation.

They also tug at our imagination. In western cultures, superstition is rife with the malevolence of dragonflies. Many American kids grew up to face the perils of telling the truth because they believed dragonflies would sew up their mouths if they lied. The same fate awaited those who cursed.

In some American Indian and European folk tales, dragonflies are associated with dark forces, sent by the devil to stir up trouble in the world.

By contrast, Japanese folklore holds the dragonfly in much higher regard. It is an auspicious symbol and national emblem, representing the spirit of the rice plant. (They both thrive in watery places.) Japan itself is sometimes referred to as Akitsushmi, or Dragonfly Island. And Samurai warriors often incorporated the dragonfly in their family crests because of its cunning and skill in combat. Little did they know just how cunning it is.

Three years ago, researchers at the Centre for Visual Sciences at the Australian National University in Canberra reported in the journal Nature an extraordinary finding about dragonfly tactics in aerial combat.

The researchers set up a pair of cameras to record dragonfly dogfights over a pond. Male dragonflies are fiercely territorial and will chase and harass competing males and other interloping insects over great distances, ramming them in midair until they get the message and go away. The cameras were positioned so the plight paths of both the pursuer and its target could be plotted in three dimensions.

What the researchers found was that the attacking dragonflies were using stealth tactics that employed motion camouflage. Motion camouflage sounds oxymoronic since most species in nature that employ camouflage depend on absolute stillness to escape notice. The point is to blend into the background. But when the background itself is constantly moving, as it is in aerial combat, motion camouflage, or stillness in the context of motion, becomes possible.

After analyzing the flight paths of the dragonfly attacker and its target, the researchers realized that the dragonfly was altering its path with incredible speed and precision to maintain its own image constantly in the same region of the retina of its prey while steadily closing in for the strike.

With the help of this dragonfly data, a mathematician at the University of Manchester in Britain has worked out the mathematical equations underlying motion camouflage. So now, after 300 million years, I expect it won’t be long before the Air Force cracks the secret and figures out how to program its stealth fighters to mimic dragonflies. Let’s hope this contribution to military science won’t ultimately contribute to our own extinction as a species. (Who knows what dangerous secrets the dragonflies whispered in the ears of dinosaurs?)

Dragonflies don’t need to impress me with their secrets. I’m content watching the incredible variety of these insects — the clubtails, spineylegs, emeralds, shadowdragons, skimmers, pondhawks, and darners — as they work tirelessly to bring about the extinction of the mosquitoes in my yard. Each one eats 600 in the course of a day. Only the homely bats do a better job — and bats do their work in complete darkness. It shows them to their best advantage.

If I may choose the currency of my riches, I’ll pick dragonflies over bats any day.

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