Here Be Dragons

Butterfly numbers are down this year in Tidewater Virginia. Since 1999 when local naturalists began annual surveys there have been large fluctuations from year-to-year, but the numbers recorded this year on a hot July day were almost half the reckoning of last year, although most of the same species were seen (29 in all).

This scarcity was obvious from the moment surveyors set off for butterfly-favored habitats across the counties of Surry and James City. We had a hunch that a cold winter had killed the adults and pupae during their hibernation, but why then had so many other insects and arachnids fared okay? The only other reported paucity—and a welcome one—was the impression that there were fewer mosquitoes around. But the dragonfly population had soared. The abundance of golden-winged skimmers was astonishing. You could see hundreds (countless) at a time and in many locations throughout the study area buzzing hither and thither in frenzy. They were probably searching with their large, bulbous eyes to catch a fly or a date. But there was an Aha! moment when we saw another species on a branch munching an orange sulphur butterfly.

dragonfly & butterfly
Dragonfly eating an orange sulphur. Courtesy of Teta Kain

There is not much in common between a dragonfly and the serpentine, fire-breathing dragon of fables, but they are both voracious carnivores. Dragonflies have complete mastery of the air—they can fly forwards, backwards, sideways, even upside down, at over 30 mph after prey, and can eat as much as their own body weight in a day. With such aerobatic skills and all-round vision they should be the inspiration of drone modelers at the Pentagon. We wondered if dragonflies were responsible for the dearth of butterflies. Maybe.

As I write this post in the Allegheny Mountains of West Virginia butterflies are as common as they were a year ago. In a fifteen minute walk across a meadow I spotted two species of swallowtails, two of fritillaries, American coppers, wood satyrs, sulphurs, whites, a bevy of skipper species, and others too fast-flying to identify. All were plentiful, but there were no dragonflies. I saw none throughout the district because there is no standing water for them to breed.

Dragonfly
Golden-winged skimmer (Libellula auripennis)

These observations seemed to clinch a simple explanation—one of cause and effect. When prey species were abundant in Tidewater last year the dragonflies produced a bumper brood that emerged as adults in 2014 to consume all the insects they could catch. They are highly efficient predators, even more so than lions and tigers, capturing prey 95 times out of 100 attempts.  The butterfly population may take a few years to recover and, unless they are a minor fraction of the diet, dragonflies will go hungry next year and not peak again until after a good butterfly year.

It’s a neat story and a familiar one of population cycles that Charles Elton (1900-1991) pioneered. He was an Oxford biologist who, as much as anyone, transformed the craft of the naturalist to the science of ecology. He was fascinated by the 3-5 year cycles of Arctic lemmings; he found their numbers rose year after year until they ate out their food supply and died in a Malthusian catastrophe of starvation (not by jumping off cliffs). Bringing the lemming story up to date, there was an irruption of snowy owls as far south as the Carolinas in the 2013-14 winter, which may be explained by a crash in the lemming population after the 2012 summer of plenty.

Neat explanations are sometimes true, but history records that after the first simple hypothesis is planted a thicket of other explanations grow up as scientists probe deeper, and not only in ecology.

When I was a newly-minted faculty member in Edinburgh, Professor L. Mary Pickford (1902-2002) casually made a remark in the common room one day that I have never forgotten. She had a retired as an eminent neurophysiologist who would have known Elton as a contemporary Fellow of the Royal Society (Britain’s national academy of sciences). You can imagine her like a twin of the old movie star, the very English Margaret Rutherford. Mary said that of all the changes she had witnessed in a long career in medical science one of the most dramatic was the replacement of single causes and effects by multiples. She probably had in mind her favorite research subject, the pituitary gland, for which textbooks in her youth listed a function, mostly only one, for each of its hormones. But nothing is so simple today. Prolactin, to take one example, is now claimed to have over a hundred different actions in various animals. And for another example, oxytocin has been found since that conversation with Mary to be involved in maternal behavior, anxiety, and sexual orgasm, and can no longer be considered as just a ‘birth and milking hormone.’

Likewise, Elton’s theory that lemmings periodically eat out their food supply has been extended to include complex prey-predator relationships. And, moreover, ecologists predict that their population cycles will lengthen in future as Arctic warming affects snow pack and vegetation.  Nature appears more complicated and expansive the closer we examine it and on every scale—from the menagerie of sub-atomic particles through the structure and biochemistry of cells to galaxies at the known edge of the universe.

As a student cramming for exams I remember craving for simple stories in physiology, and found the deepening and broadening of knowledge to be frustrating, if not annoying, jolts to work harder! But I now think that complexity is something to celebrate, and if it seems bottomless perhaps we ought to approach it with reverent awe.  And so I am musing whether our hunch about dragonflies is too simplistic, although I suspect we will never be sure. I hope we are becoming a little more humble in claiming knowledge and cast off the certainties that old cartographers had when they printed on the far side of oceans, Here Be Dragons.

Dragonfly
Blue dasher (Pachydiplax longipennis)

Next Post: Doc Bamboo

 

Nose to Proboscis

Nose to probscis#1Dogs get really close when they want to check something out. Noses twitch and nares gape when air is being drawn from an object of curiosity across their olfactory epithelium, which can sense far more odors than we can ever imagine. We depend more on eyes than noses to perceive things, and rarely get so close, although a friend who was registered blind held papers so near his face that he could smell the ink.

If our golden retriever could speak she would probably scold me for pretending to know about wildlife from observing it only at a distance. “So you think you are a naturalist now?” she would growl. If she could, Lilah would tell me what butterflies smell like, why they like some flowers instead of others, and what they look like at very close quarters. So the other day I crept up to a flight of butterflies in our garden to see if I was missing something.

Zebra swallowtail
Zebra swallowtail

This has been a bumper year for swallowtails in Virginia (monarchs are scarce). Most sunny days, there are more than a dozen from four species hovering over the Lantana and Zinnia before alighting on a flower. Although among the strongest flyers of their family, they allowed me to inch towards them as they rested to feed until I was so close to one of them that my eyes were straining.

Eastern tiger swallowtail
Eastern tiger swallowtail

It is a long time since I have had that close a communion with an insect; I normally never get nearer than crunching a cockroach underfoot. But the head-to-head encounter with an Eastern tiger swallowtail almost felt personal, although I wonder what it made of me through ommatidial lenses of its compound eyes. The butterfly remained unruffled for several minutes until it had drained the nectaries of a flower and moved to the next; as calm as when I sidle up to the bar beside a taphouse customer who has an absorbing interest in his beer and doesn’t want to be disturbed.

The butterfly’s proboscis lashed back and forth like a whip, reaching its targets deep inside flower bells with amazing precision. Every sweep reached a new floret from which it could drink. Compared to this delicate tool-user, an expert fly-fisherman looks like a clumsy fool casting for trout in a pool.

Spicebush swallowtail
Spicebush swallowtail

Under the microscope, you would see the proboscis is formed from two parts that are zippered together to make a tube. It is an extension of an insect’s mouth, and nothing like the noses of elephants and monkeys that are sometimes called proboscises. Since it looks like a flexible drinking straw, you might think that butterflies suck nectar into their bodies, but the effort of drawing the viscous fluid through a high resistance canal would be futile. New research shows that sucking is secondary: butterflies use capillary action like a paper towel to soak up fluid, which does not require expending any energy. Had I not stooped that day to watch the aerial plumber, I would never have wondered how it manages to feed, never run back to peruse an entomology journal, and never marveled more at the vigor and beauty of a wild creature. Wonder is an unexpected reward when you get close enough to something that spikes your curiosity. Not since I used to sketch and paint have I gazed so intently at any creature. That seems a shameful admission for a biologist, although it is all too common to become careless of things that once inspired us.

Our traveling microscope. R. Wasserlein, Berlin (c. 1880)
Our traveling microscope. R. Wasserlein, Berlin (c. 1880)

In the Nineteenth Century, many gentlemen took up nature study as an absorbing pastime. It was an era of greater leisure and fewer distractions, when explorers were bringing home weird and wonderful specimens from remote lands, and there was feverish excitement about new scientific theories. We have a small collection of scientific artifacts from that period. I imagine a Victorian gentleman packing one of our traveling microscopes in his trunk for a journey by stagecoach or train. He would have taken it to study specimens collected on his trip—parts of a flower head, lichen prized from a rock, scales on a butterfly’s wing, and so on. He wanted a closer encounter with things that nudged his curiosity. Nowadays, we can explore a much wider world through smart phones and tablets that connect us with the WWW, but although I love those gadgets they are no substitute for directly engaging the senses with the real objects of our interest.

Opening your phone in Starbucks to visit a butterfly website is unlikely to attract attention from other customers, but if you pulled out a microscope from your bag to examine a bug floating on your coffee you would turn heads. And if you were seen lying spread-eagled in a meadow watching the microfauna creeping between stalks, like a Gulliver observing Lilliputians, you might be called eccentric. But there should be no embarrassment when curiosity stirs us to draw close for a better view, only pity if we become estranged from the very things that at one time aroused our imagination, and perhaps to such a pitch that it had lifelong impact or led to a career. Like a marriage strained by work, there are many distractions that conspire against the personal engagement we once had.

A medical researcher burdened with grant applications, manuscripts, faculty meetings, and lectures may no longer have time to study under the microscope or to interview patients, but depend on a second-hand connection with his subjects provided by assistants. A landscape artist may lose the inclination to set up an easel en plein air, but paints instead from photographs. A busy surgeon has few opportunities to speak to his patients because he usually encounters them anesthetized. A teacher who is promoted to administration rarely sees kids any more. And a politician who becomes a hot-shot spends less time face-to-face with constituents.

Nose to probscis#2It is hard casting aside distractions, especially when they are so abundant, and so easy to forget the things that once impelled us. For me, it took stepping out of a career and a dog nosing a butterfly to remind me about the wonder of nature.

Next Post: A Hunter’s Heart