Seventeen Year Itch

Back in 1996, Bill Clinton was still in his first term of office, Charles and Diana agreed to divorce, the Unabomber was apprehended, and Ella Fitzgerald died. That year I hadn’t even dreamed of moving permanently to North America: I was living in Yorkshire where mad cow disease was seizing the headlines in England. While so much history has flowed through newspaper presses since then, Brood II cicadas were all the while secretly sucking at tree roots waiting for the calendar to flip over to 2013.

I encountered the brood a couple of weeks ago at a rest area on the I-64 west of Richmond.  The first thing travelers noticed after stepping out of their cars was a chirping racket coming from every direction. I had heard the sound only once before when a 13-year brood of cicadas was emerging near home in 2011. This year it is the turn of the 17-year ensemble to sing.cicada on grass

For a few weeks every 17 years local residents have sleepless nights. The noise can be as loud as a passing truck, and at 90 decibels reaches a level at which the Occupational and Safety Administration warns we should not be exposed to for more than 8 hours a day to avoid hearing damage. Not being respecters of regulations, male cicadas chirp round the clock.

They are among the great wonders of the insect world, but not only because they have one of the longest life cycles. The question that intrigues me more is how they manage to coordinate mass emergence.  When ground temperatures rise above 64 °F (18 °C) in the Year of the Brood, the fossorial cicada nymphs start to burrow upwards, breaking the surface first at the southern edge of their range (North Carolina) and progressively towards northern limits (Connecticut).  Soon there are incalculable billions above ground, more than a million per acre, but during intervening years you are unlikely to see any at all.  So precise is their timing that local residents can plan when to be on vacation in 2030 during the next big pulse.

They look scary and are the biggest of their kind. They are an inch-and-a-half long with bulging red eyes, orange wing veins and leg stripes, and through their transparent wings you can see a black cigar-shaped body.  They look like bugs in zoot suits and were given the marvelous scientific name, Magicicada septendecim.

I was a member of a naturalist group heading for a wildlife center in the Blue Ridge, but the cicadas in the car park – not you would think the most auspicious place to watch wildlife – were the most memorable sights of the day. They were thought to be a bad omen by superstitious early colonists, who assumed (wrongly) that they were the same as locusts in the Bible which warned in the Book of Revelation: “Then from the smoke came locusts on the earth …” I guess that every seventeen (or thirteen years) there were particularly fiery sermons from the pulpit about the seven last plagues of Armageddon.

For all their fearsome appearance, they are harmless insects. They don’t bite or sting, nor do they eat vegetation as true locusts do. They can cause minor tree damage from “flagging” (browning) during nest-building, but are generally rather beneficial. Soon after mating and egg-laying the adults die, providing food for critters and fertilizing the soil. The only remaining cicadas are immature “instar larvae” hatched from eggs. These nymphs fall from the tree canopy to the ground where those that avoid predation burrow underground to find juicy roots to suck on … and on … and on until the calendar turns.

For the most part, the distribution of 17-year broods and 13-year broods don’t overlap, although they evolved from a common stock a few million years ago.  Today there are 15 broods in North America, twelve with 17-year cycles and three with 13-year, and you will not find them anywhere else.  Of the 3,000 species of cicada worldwide, only seven have periodical behavior.

Burrows and shells from which cicadas emerged in the car park
Burrows and shells from which cicadas emerged in the car park

We watched hordes of them lumbering up tree trunks and walls; we saw many flying unsteadily like old flying boats, often crashing into branches or to the ground where robins were waiting to pounce. For a small bird, a cicada is hamburger-sized (and probably just as nutritious), so the eaters were soon sated. Everywhere across the hard-trodden ground there were holes, about ten to the square yard and a little larger than earthworms make. These were the burrows from which cicadas had recently emerged, and scattered close by were the transparent brown shells (exuvia) which they had worn for so many years underground. They gave us a spectacle I may never see or hear again.

The greatest enigmas are how they know the time, and why coordinate their emergence instead of being independent like most insects. We know of genes that regulate daily cycles in animals, but I can’t understand how molecules make a 17-year timer. And if cicada nymphs were synchronizing eruption by communicating with each other underground, it stumps my imagination.  Perhaps it serves to overwhelm the appetites of predators so that at least some survive to breed, although that theory is controversial. A similar explanation has been offered for mast seeding of long-lived plants. Last year was a mast year for oaks, with acorns lying so thick in our yard that every step sounded like walking on cornflakes.  But mast years are unpredictable – they can be consecutive or after long gaps – whereas cicada years can be written into almanacs for years, even centuries, ahead.cicada on blue

There are few pat answers in nature and the life sciences. That was frustrating when I was a student preparing for exams, but now I think the mysteries are far more wonderful than the facts.

Next Post: Baby’s first picture

A Death Observed

Virginia died yesterday, a life sown, grown, and ripened in the state that gave her a name. She slipped away gently in the night, her passing unnoticed until she had gone. It’s often like that.

Our neighbor was just one of 154,000 people who passed that day, but the only one whom we knew and loved.  Born to a farming family, she was married twice, widowed once, and bore some private tragedies and hardships that everyone who lives to ninety must expect. Her only child died in infancy; the first marriage was broken by grief; she was a victim of fraudsters; two years ago when her home was laid waste by a hurricane she too was almost snuffed out; and she endured a growing burden of illness at the end, with pain …cameo

Virginia lived the two lives defined by Susan Sontag: a healthy one and the other.  Illness is the night side of life, a more onerous citizenship. She bore it bravely before crossing over the frontier to a shadowy territory, so familiar in name yet so strange in nature. Like other partings, it left me wondering how she could have flown so far and so quickly when she was so vividly amongst us the day before.

Can biologists say anything worth a whistle about that most mysterious of journeys? Not much! Ours is the science of life, and it’s not our job to turn the coin to read the other side. And those who study the opposite pole of the lifespan, like me, are least qualified; we are a happy bunch, watching embryos negotiate uncertainties until they emerge triumphant and hopeful of a full span ahead of them.  Writing this post was a way of working through uneasy thoughts, casting back to memories of lost parents and friends, certainly not expecting Virginia’s passing to be revelatory, only assured that empty feelings will be filled later by the business of living.

***

Death is either an instant or an eternity; I can’t decide between them.  But because it is not in time it is outside the realm of science, beyond the reach of the scientific method.  Talk about thanascience and I will tell you it’s nonscience.

Thanatos was a Greek daemon, a sort of nature spirit or custodian of the departed who served the Gods with his brother Hypnos (Sleep). He was (is) the dreaded leveler. Achilles, who knew a thing or two, advised Odysseus: Death comes alike to the idle man and to him that works much. While he mercifully bears away fallen warriors from the battlefield, Thanatos knows no justice, taking Virginia’s son, Skippy, after a medical error long before he came back to release her from pain and frailty.

Last week I passed a ramp on the I-64 outside Charlottesville where I remembered years ago the traffic was slowing to pass an accident. A highway patrolman and another driver stood beside a bulging yellow tarp spread beside a motorbike on its side. No one had yet picked up the shoe from the middle of the lane. The shoe, the shoe … that’s the thing I most remember every time I pass that point. Perhaps the poignancy of its emptiness is why I can’t forget it. How much harder it is to accept an untimely death than when time’s arrow has had its full flight before coming to ground. What then is aging?

Death_Sleep
Death & Sleep carry a warrior. @Trustees of British Museum

In his speech, All the world’s a stage, Jaques catalogued seven stages of life, ending with sans teeth … sans everything. Then the fool declared … from hour to hour, we rot and rot; and thereby hangs a tale (As You Like It).

Biologists protest his picture of aging. Healthy bodies don’t rot away gradually with the years, and death doesn’t have commerce with life by trading time for vitality, though statisticians might argue.  Aging is a slippery subject, still full of secrets.  We have discovered many chronometers inside cells, but a master timepiece showing how far we have traveled, how far to go, is still elusive – if one exists at all. To measure biological aging we fall back on insurance actuaries and government statistics whose data show the annual risk of dying increases at a compound rate of interest, called the force of mortality. We are not gradually dying from the moment of birth, as Jaques would have it, but the probability starts climbing after childhood.

The math predicts our chances of dying double every seven years, a prime number that was laden with mystical significance in the past. As people live longer on average nowadays, sailing past the old prescription of three score years and ten ought to fill us with more gratitude than rage against the closing of the light. We push towards the limits set by biology and genetics, and bioengineering may well succeed in helping future generations to pass Madame Calment’s record of 122 years.

It is awesome that life forces inside cells triumph for long over the Second Law of Thermodynamics which commits all non-living matter to decomposition and heat death.  Life succeeds against the odds but aging is neither its price nor is it ubiquitous: some animals and trees have indeterminate lifespans, are exempt from the signs and statistics of age, although none is immortal, all eventually fall to accidents or ‘Acts of God’.  Death is the tipping point on a gradient when vitality can no longer sustain life: and then the fall is precipitous.

While Thanatos bides his time, his junior agents are busy pruning the body, mostly for benign or even beneficial ends.  Cell death is happening everywhere all the time, and is often executed by a genetic program called apoptosis, meaning falling leaves, a Greek expression coined by my former colleagues in Edinburgh.  Trees continue to live after shedding their leaves in fall. In our bodies, healthy cells are sacrificed to make more a perfect form, like trimming surplus cells to create digits from the club hand of an embryo, and removing unhealthy cells, including cancer, if not always with enough gusto.  That kind of death we can celebrate.

But when he snatches a pretty bird with a red claw from our feeder it grieves us, yet the hawk and its chicks would starve on a diet of nuts and berries.  His work is paradoxical, taking one so another can thrive, keeping the wheel of life turning. Yet what is wise in nature seems so cruel when it strikes home, and prematurely. Isaiah may have reassured his followers, All will be well, but can he comfort us?

***

When the seventh seal was opened in the Book of Revelation, there was silence in heaven. The late Ingmar Bergman created an agonizing existential silence in his 1957 black and white movie, The Seventh Seal. Antonius Block, a Swedish knight returning from the Crusades to his homeland ravaged by the Black Death meets Death dressed as a hooded monk. As they play chess on the beach, his early hopes of winning are dashed, and after he knocks the pieces over Thanatos remembers every place on the board.

When a subject is too much to bear we laugh it off. In Death Knocks, Woody Allen’s hilarious parody of The Seal, Nat Ackerman in a New York apartment receives a surprise visitor in a black cape carrying a broken scythe over his shoulder.

Nat: “You look a bit like me.”

Death: “Who should I look like? I’m your death.”

Nat protests that he had come too soon, while still enjoying rude health. Then he challenges him to a game of gin rummy, winning a Pyrrhic victory.

As in Markus Zusak’s book set in Nazi Germany, The Book Thief, Death in all these stories is like his Greek forerunner, not the master of the house, more like a janitor with a solemn duty which he carries out efficiently without knowing or even asking the reason why.

Biology too, if just in this regard, is barren soil, offering only an endless dark night of the soul. Apart from religious belief, the humanities is the other spirit struggling for meaning, even if in honest moments it admits no more than to circle back to where it began. In his last big poem, Four Quartets, T.S. Eliot wrestles for words at the borderline of time and eternity, traveling from a mysterious revelation in the rose garden at Burnt Norton to East Coker where the heavy feet of rustic villagers clump nuptial dances, and he finally stands by the cornfield  nourished by his ancestors underground. People take what they will from literature, and from science too for that matter, but for a biologist these metaphors ring truer than, say, the mysticism of William Blake for their familiar organic-ness and earthy order. At the center of a turning wheel of life Eliot observes stillness, a peace like Dante and Hindu traditions observed long ago.

When we lit candles as a memorial for Virginia, my thoughts wandered to a memory of tramping through swampland where I once saw a dancing blue light, the will-o’-the-wisp, eerily emanating from the stinking bog of decaying biological matter. It wasn’t a hostile flicker, nothing like the devilish faerie light of Milton’s Paradise Lost drawing travelers to their doom, and I knew it was only a manifestation of the carbon cycle. But I liked the metaphor of the burning bog, almost Old Testament-like, gently drawing you closer until the animation suddenly vanished.

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