vignettes: wildflowers and dragonflies

8/9/2019 VIGNETTES: Wildflowers and Dragonflies

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Wildflowers

and Dragonflies



Wildflowers and Dragonflies

Some ten years ago a Catholic retreat in Ipswich was acquired by New EnglandBioLabs. The parcel of land involved -- large, with gently rolling hills -- is beautifully landscaped. The once magnificent old brick buildings have been restored, and tothem have been added contemporary glass and steel buildings. The two might coexistin discomfort, were it for the magnificent changes made to the grounds.

In 2000 the company set aside the lower, level part of the grounds near thehighway (Route 1A) as a public soccer pitch, and planted the large, steep hillsideabove the pitch in tall wildflowers. One day I parked on the road just below theflowers and stood there feeling as if I had just stepped into a Renoir landscape. Itrecalled the first time I saw The Wizard of Oz, when Dorothy steps through a blackand white doorway into the striking colors of Oz.

The company has since placed original contemporary sculptures all about thegrounds, as well as a striking abstract that covers most of a side of one building.

One summer day when I visited here, hundreds of dragonflies were darting

Common bluetail damselfly (Ischnura heterosticta). Photo copied under terms of the GNU Free Documentation License, Version 1.2.

Credit Fir0002/Flagstaffotos.



about, not in mating or territorial behavior but just zipping about and giving each otherplenty of air space. I couldn't figure out what they were doing until I faced downhill,into the sun, to watch the children at soccer practice. Only then did I notice that theair was filled with midges too tiny to see until back-lighted by the sun. The dragonflies

were feeding on these.One other day that summer, while sitting by the outdoor pool at the Manchester

Athletic Club, I noticed a large dragonfly that had claimed the entire pool as itsterritory. It would hover above the pool, oblivious to wildly splashing children, and atthe first sign of another dragonfly would flash to that point so quickly that my eye couldscarcely follow. After each intruder was repelled (or courted?), the dragonfly wouldreturn to the same precise spot over the pool.

Male dragonflies are very territorial. When you see two adults chasing eachother on the wing, it is often one male chasing another from its territory. When yousee two dragonflies flying attached to one another, it’s nearly always a male andfemale mating.

Worldwide, the Odonata order of insects (dragonflies and damselflies) includesmore than 5,000 individual species. They exist in many countries around the world.

Within the United States, there are about 400 species of Odonata. Dragonflies aresome of the most ferocious predators of the insect world, both as larvae and as adults.

You may see them for only short periods each year, but they live longer than you mightthink. Most of the adults you see have spent much more time in the larval stage (up tothree years) as aquatic predators than they will as adults. The adult, winged stagelasts only a few weeks. Mating is the primary reason for their winged stage, so when

you see a winged dragonfly, you know it's approaching the end of its lifespan. They’rehighly beneficial to us, for they consume large quantities of flies and other pests.

Dragonflies are among the most ancient of the flying insects. Fossils with 27-inch wingspans have been found dating back over 200 million years. Among extantspecies, the largest have wingspans of five to six inches.

When I was young we called all dragonflies "darning needles." Our parents

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perpetuated the myth that dragonflies could sew up the mouths of naughty children.In other parts of the country, children were taught to believe that sleeping outside putthem at risk of having their eyes sewn shut by a dragonfly. [Earlier generations neverran out of ways to keep children scared straight.] These insects are often curiousabout people and will fly around you for that reason, but they do not sting or bite.

In Massachusetts alonethere are 120 species of dragonfly. Most often seen(or so I’m told) is theCommon Green Darner( Anax junius). [Does thename Darner hark back tosewing up the mouths of naughty children?] The ones Isee on Cape Ann lack the bigheads and transparent wingsof the Anax junius shown atright. Most of those I've beenseeing more cloself resemble

Variable Dancers ( Argia

fumipennis), but these aredamselflies.

Damselflies aregenerally smaller thandragonflies, and weakerfliers. A key field point is that

damselflies at rest fold their wings along and parallel totheir bodies, whereasdragonflies rest with their

wings fully extended.Some dragonfly species aremigratory, and somemigrations are spectacularflights involving hundreds of thousands, even a million ormore, individuals. Unlikebirds, a given generation of dragonflies migrates only one

way, with the offspring of thatgeneration completing the round trip at a later time. [Not unlike Monarch butterflies(see).]By all rights, dragonflies shouldn't be able to fly as well as they do. Their flightmechanism is ancient, over 300 million years old -- obsolete, really.

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Bees, flies and mosquitoes are the flying aces of the insect world. Their flightmuscles attach to the top of the thorax, which fits onto the bottom like a lid. When themuscles twitch, the lid squeezes down and pulls the wing-base down with it. This flipsthe rest of the wing up. When the muscles relax, the lid bulges upward again and theprocess is reversed. This mechanism is what enables these insects to flap their wings

hundreds of times per second.The flight muscles of dragonflies attach directly to the wings. When the muscle

contracts, the wing beats. This rules out the rapid flight of bees and flies, yet clearly dragonflies are magnificent flying machines. Their four wings also allow them tohover, fly backward, change direction instantaneously, and fly so fast in a straight line,at speeds up to 30 miles per hour, that the eye can barely follow them. In fact, they fly

well enough to prey on flies and mosquitoes, those very insects that have left them inthe evolutionary dust.

The dragonfly's secret is genetic inventiveness. Its basic flight mechanism may be obsolete, but the species has been re-engineering that mechanism in ways thatscientists are only now beginning to learn. And the retro-fitting began early. Expertson the subject of ancient insect flight have discovered clever aerodynamic structuresin the wings of a dragonfly fossil 320 million years old (only about ten million yearsafter the oldest known flying insects). Other research has shown that dragonfly wingsderive energy from tiny whirlpools of air that are created around them. The dragonfly may be ancient, but it's far from primitive.

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vignettes: wildflowers and dragonflies

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