Posts Tagged ‘dragonflies’

Oiling The Devil’s Darning Needle

June 6th, 2010 | Meera

In the fall of 1889, just past the height of bug-season in his home state, Henry C. M’Cook—then-Vice-President of the Academy of Natural Sciences of Philadelphia and Vice-Director of the American Entomological Society—wrote a lively article for the North American Review in which he outlined ways of mitigating the reign of the pestilential mosquito. Four pages into his arguments, he found himself distracted (as we all are, from time to time) by a dragonfly.

I have read of a school—if memory serves me truly, it was situate in that highly-developed center of American civilization, New York City—whose session was broken up by the advent of an innocent dragon-fly through an open window. An alarm raised by one scholar passed through the entire room: “A devil’s darning needle! A devil’s darning needle!” The ominous phrase, piped in the shrill quaver of terrified childhood, alarmed the teacher, and the agitation became so general that the school had to be dismissed as an act of humanity.

I love the gentle sarcasm in that. “Act of humanity.” Dr. M’Cook, you were one sly scientist.

In their 2005 book A Dazzle of Dragonflies, Forrest Mitchell and James Lasswell explain that the dragonfly-epithet “devil’s darning needle” has its origins in the Europe of the Middle Ages. The long and slender shape of the insect’s body, combined with the superstitious belief that it, like the fly—consort of Beelzebub—was in league with the darkest of forces, produced a myth durable enough to make the journey with the colonists to the United States. Today in Iowa, the authors write, “devil’s darning needles sew together the fingers or toes of a person who falls asleep…in Kansas, they may sew up the mouths of scolding women, saucy children…and profane men.”

Dragonflies, of course, do no such thing. In fact, creatures belonging to the order Odonata—Latin for “toothed,” a reference to the chewing mandibles dragonflies share with most other insects—and the infraorder Anisoptera—Latin for “unequal wings,” because dragonflies have broader hindwings than forewings—have no sting, let alone needlepoint. They are perfectly harmless to humans, if not to their prey: smaller insects, including ants, bees, and the mosquitoes that so irritated M’Cook.

I tell you these things today because I spent the morning at Promontory Point, winding my way along the rocky strand where Lake Michigan hits Hyde Park—and, by the by, watching a levitation of dragonflies dart back and forth across the path and wheel between tall grasses. (I could find no consensus on the proper collective noun for dragonflies, if any exists. Mitchell and Lasswell offer dazzle; I went my own way.) Whatever you call them, they were magnificent: swift and glittering and alarmingly unpredictable—I had to duck, once, to get out of the way. So erratic were their flight paths that they seemed almost invulnerable to the greedy swoops of the ring-billed gulls that flew overhead.

I’m not sure which of the hundred or so species of dragonfly known to be seen in Illinois I was looking at. But there must have been at least two distinct kinds dancing in between each others’ wings, because all were fully grown, but some were large and some were small. Dragonflies, like almost all other winged insects, have already gone through their final molt by the time they are able to fly, and so every dragon in the air is an adult.

I saw a flash of blue, though I do not think what I saw was little enough to have been the impossibly wee Elfin Skimmer (Nannothemis bella). And it is a little late now for the Green Darner (Anax junius), a common sight around Chicago in the spring and fall. (The Darner is one of a tiny number of dragonflies that migrate seasonally. Recent study suggests that the most persevering of these creatures may cover round-trip distances as long as 16,000 kilometers. This is, coincidentally, nearly identical to the length of my own annual migration between Chicago and Singapore—a fact that floors me. When I get off that plane, I am bone-tired, dog-tired, dead-tired: but apparently not dragonfly-tired. I am shamed by insect-endurance.)

what keeps you steady

The other reason I tell you these things today is that the last time I got as close to an Anisopteran as I did this morning, I was in the New Orleans bayou, a year after Katrina. I remember being surprised then by their calm fearlessness: the way they would land on the edges of leaves right there under my nose, and turn their heads, set with eyes as heavy and faceted as precious stones. They let me come close enough to feel the air brush away from their wings as they took off again, and maybe their tranquility came from the sure and certain knowledge that they far outnumbered our curious band of swamp explorers. The coastal plains of Louisiana are dragonfly country. The air there is thick with the sound of their flight.

Which is why it is so hard to think of the way that country has changed over the past six weeks.

Consider this:

I. Oil Prevents Emergence

By the time we see a dragonfly, it has reached the end of its multifarious life cycle. Female dragonflies lay their eggs in or near water, and the nymph and larval stages both exist aquatically. The larvae of some species may spend a few months or as long as several years underwater before crawling above the surface to metamorphose into their final, satin-winged forms.

(I love thinking about this life, by the way—a life so focused on growth and preparation, in which the fulfillment of one’s basic plan for existence is vital, of course, but temporally inconsequential. I imagine myself like this right now, hunkered down, eating and growing and having no idea of what ultimate shape I will take, what satin wings I will have.)

But on the Gulf Coast, oil has flowed into the salt marshes where dragonflies lay their eggs—spread itself like a blanket over their underwater atmosphere. As long as its black covering remains, dragonfly larvae from eggs laid weeks or months or years ago will be unable to split the water’s surface without at once covering themselves in pitch.

II. Oil Looks Better Than Water

Like many other insects, fish, and mammals (though not humans), dragonflies are sensitive to the presence of polarized light. The light receptor cells in their retinas are full of the photoreceptive protein called rhodopsin. So are ours. But in the human eye, rhodopsin molecules within each cell are arranged haphazardly, with their axes running at random angles. As a result, our eyes collect light indiscriminately. We have no way of differentiating scattered light, whose waves vibrate in all directions, from polarized light—in which vibrations have been restricted to a single plane.

In dragonfly eyes, rhodopsin molecules within each light receptor cell are aligned in parallel. That means the molecules preferentially absorb beams of light whose waves are vibrating in the same direction and enter the eye in the same orientation: thus hitting all those neatly arranged rhodopsin molecules at just the angle towards which they collectively lean. In other words, dragonfly eyes are especially greedy for polarized light. And since large, flat bodies of water like ponds, lakes, and oceans polarize light as they reflect it, that’s a pretty helpful attribute for an insect that hunts, mates, and lay its eggs over water.

Except water isn’t the only thing that reflects polarized light. Not by a long shot. Dark-colored cars do it. Glossy black tombstones do it. Both have been shown to confuse insects like dragonflies, which often choose to mate above such objects instead of above water, and even attempt to lay their eggs on these strange, inhospitable surfaces.

And then there is crude oil. Thick, black, shiny crude oil, the kind covering vast swathes of the Gulf of Mexico at the moment. In the late 1990s, a group of Hungarian scientists found themselves intrigued by the odd behavior of dragonflies that hovered and mated around the shiny black surface of the open-air waste oil reservoir in Budapest. By comparing the number of dragonflies that were caught in traps containing plain water, salad oil, and crude oil, the researchers convincingly demonstrated that the glittering creatures “can be deceived by and attracted to crude and waste oil.” In fact, their results suggested dragonflies actually prefer crude oil to water, probably because oil more strongly polarizes light.

On the Gulf Coast, then, it seems more than likely that as we speak, dragonflies are taking oil for water.

We are oiling the devil’s darning needle—just when it would, perhaps, do very well to sew together our fingers and toes.

Photo: Gerald Herbert/AP