The Forest Unseen: A Year's Watch in Nature (16 page)

Malaria is seemingly irrelevant to my modern experience in the mandala, but this is an illusion. The mandala has been spared the chainsaw because it lies in an area set aside by the University of the South. This university brought me here also. What brought the university to this hillside? Malaria, among other things. Like many of the older universities in the East, the school is located on a plateau, away from the swamps that breed malaria and yellow fever. The cool temperatures and relative freedom of the Tennessee hills from mosquitoes made them an ideal place to send the offspring of the southern gentry. The school year ran through the summer, allowing students to escape the heat and disease of the cities. School was closed and abandoned in the winter, when the mosquitoes of Atlanta, New Orleans, and Birmingham were in abeyance. This prime location helped cement the university to the mountaintop, ensuring its viability long after one of its primary benefactors, the malarial parasite, had faded from the land.

The atoms that make up my blood were propelled to the mandala by these biological forces of history, and it is appropriate that a mosquito should carry away some of them to rearrange them into a raft of eggs. This physical connection to the rest of nature is often unseen. The mosquito bite, the breath, the mouthful are acts that create a community, that keep us welded into existence, but that mostly pass unacknowledged. A few people say grace at a meal, but no one does so with every inhalation or insect bite. This unconsciousness is partly self-defense. The connections through the millions of molecules we eat or breathe or lose to mosquitoes are too many, too multifariously complex for us to attempt comprehension.

·     ·     ·

The whining reminders of interconnectedness persecute me as I sit at the mandala, so I pull up the hood of my sweatshirt and tuck my hands into the sleeves, trying to slow the barrage. I peer over the lip of my cocoon and study the evidence of another kind of atomic flow. A snail has been smashed on the rock beside me. A few translucent crumbs of the honey-colored shell lie on the surface of the rock. These are the remains of a bird’s calcium-hungry feast.

The crushed snail in the mandala is one stream among many in the great springtime flow of calcium from the soil to the air. Breeding female birds scour the forest for snails, greedy for the sheets of calcium carbonate on the snails’ backs. Such hunger is well founded. Without a boost of dietary calcium the birds cannot make their chalky eggshells.

Once a snail has been swallowed by a bird, the shell is first ground up in the bird’s gizzard, crushed by a knot of muscle and pieces of hard sand. The calcium then gradually dissolves into the mushy gut and is pumped across the walls of the intestines into the bloodstream. If the bird is laying eggs that day, the calcium may go straight to the reproductive organs. If not, it will go to special calcium storage areas in the core of the long bones of the bird’s wings and legs. This “medullary bone” is produced only in sexually active females. Over the course of a few weeks the medullary bone is built up in preparation for egg laying, then completely disassembled as the eggs are laid. Female birds take to heart Thoreau’s wish to “suck out all the marrow of life”—they suck dry their own bones to make new life each spring.

The sucked calcium travels through the blood to the shell gland. Here the calcium carbonate leaves the blood and is added in layers to the egg. The shell gland is the last stop through the tube that carries the egg from a bird’s ovaries to the outside world. The earlier stages of this journey wrapped the egg in albumen, then two layers of tough membrane. The outermost membrane is studded with tiny pimples that
bristle with complex proteins and sugar molecules. These attract calcium carbonate crystals in the shell gland and act as centers from which the crystals can grow. Like sprawling cities, the crystals build on one another and eventually join, creating a mosaic across the surface of the egg. In a few places the crystals fail to meet, leaving an untiled hole in the mosaic that will become a breathing pore extending from this first layer of the eggshell all the way to the surface of the completed shell. The next layer of calcium carbonate grows on top of the first, creating a shell made from pillars of calcium crystals pressed closely together. Protein strands weave across these pillars, adding reinforcement to the shell. When the thickest layer of the shell is complete, the shell gland lays a pavement of flat crystals over the shell surface and then paints the pavement with a final protective layer of protein. Thus has the snail’s shell been uncoiled, rebuilt into an avian cocoon.

As the young bird grows inside the egg it pulls calcium out of the shell, gradually etching away at the walls of its home, and turns the calcium into bone. These bones may fly to South America and be deposited in the soil of the rain forest, or the calcium may return to the sea in a migrant-killing autumn storm. Or, the bones may fly back to these forests next spring and, when the bird lays her eggs, the calcium may again be used in an eggshell whose remains may be grazed on by snails, returning the calcium to the mandala. These journeys will weave in and out of other lives, knitting together the multidimensional cloth of life. My blood may join the snail’s shell in a young bird that eats or is bitten by a passing mosquito, or we may meet later, in millennia, at the bottom of the ocean in a crab’s claw or the gut of a worm.

Winds of human technology blow at this cloth, billowing it in unpredictable directions. Atoms of sulfur that were locked into fossil plants when they died in ancient swamps are now tossed into the atmosphere when we burn coal to fuel our culture. The sulfur turns to sulfuric acid, rains down on the mandala, and acidifies the soil. This acidic fossil rain tips the chemical balance against the snails, reducing their abundance. Mother birds have a harder time bingeing
on calcium and so breed less successfully, or not at all. Perhaps fewer birds will mean less blood for mosquitoes, or fewer predatory beaks? Viruses like West Nile that thrive in wild birds may, in turn, be touched by the changed bird populations. This ripple in the cloth floats across the forest, perhaps finding a hem at which to end, perhaps floating on forever, drifting through the mosquitoes, viruses, humans, ever outward.

A
tick perches at the tip of a viburnum branch, a few inches from my knee. I suppress the urge to flick the pest away. Instead, I lean in to see the tick for its own sake, trying to look beyond my quick mental dismissal of it as a mere pest. The tick senses my approach and lifts the front four of its eight legs in a frenzied wave, grasping at the air. I wait, still, breath held, and the tick relaxes back into its original posture with just its front pair of legs raised in a prophetlike salute to the sky. My eye is so close that I see tiny scalloped ornamentations around the edge of the tick’s leathery oval body. The raised legs have translucent feet at their ends, each of which catches the sun and glows. In the center of the back is a white spot, identifying the animal as an adult female lone star tick. The chestnut color from the rest of the body seems to bleed into the star, giving it a golden sheen.

Ugly, unadorned weaponry on the tick’s head counterbalances the strange beauty of the rest of her body. The head is tiny, unnaturally so, and through my hand lens I see two stubby pillars jutting forward, barely covering a Swiss Army knife of sharp, grotesque mouthparts. I want a closer look at this nastiness, so I reach up, hold the viburnum, and pull it toward my eye. The tick senses my hand and snaps toward it, semaphoring wildly with her forelegs. This sudden catapult startles me and I jerk my hand back, releasing the branch, sorely disappointing the tick.

This foot-waving tick in the mandala is engaged in what zoologists
call questing behavior. This gives the animals a measure of Arthurian nobility, tempering our disgust at their bloodsucking habits. The image of a quest is particularly apt because both the Knights of the Round Table and the Arachnids of the Leafy Forest seek the same end: a blood-filled Grail. In the case of the lone star tick, this Grail is a warm-blooded animal, either a bird or a mammal.

The knights’ mythical quest led them to the blood from Christ’s wounds, collected in the Grail by Joseph of Arimathea. The ticks are less selective about the theological pedigree of the blood they seek, and their quest ends with molting or sex. The ticks’ quest also differs substantially in style from the journeys of the knights. Most ticks sit and wait for the Grail to come to them, then ambush it, rather than trekking across continents to hunt down their meal of blood. The tick in the mandala showed the classic approach to questing: climb up a shrub or blade of grass, position yourself at its tip, then hold out your forelimbs and wait for your victim to brush up against you.

The ticks’ quests are aided by Haller’s organs on each foreleg. These spiny indentations are packed with sensors and nerves, tuned to pick up a waft of carbon dioxide, a puff of sweat, a tiny pulse of heat, or the thudding vibrations of footsteps. The raised forelegs therefore serve both as radars and as graspers. No bird or mammal can pass near a tick without being detected by smell, touch, and temperature. When I pulled the viburnum branch and breathed on the tick, I sent its Haller’s organs into a jangling spasm, unleashing the tick’s springlike lunge at my finger.

Dehydration is the ticks’ main foe during their quests. Ticks sit in exposed locations for days, even weeks, waiting for their hosts. The wind whisks away moisture, and the sun bakes their small leathery bodies. Wandering off in search of a drink would interrupt the quest and, in many habitats, there is no water to be found. So, ticks have evolved the ability to drink water from air. They secrete a special saliva into a groove near the mouth and, like the silica gel that we use to dry our electronic gadgets, their saliva draws water out of the air. The ticks
then swallow the saliva, rehydrating themselves and continuing the quest.

The quest ends when the forelegs lock on to the skin, feathers, or hair of a potential host. The lucky tick then crawls over the host, testing the skin with its mouthparts, probing for a soft, bloody site to attack. Like cat burglars, the ticks scramble over our bodies without raising the alarm. Take a pencil and run it lightly up your arm or leg. You’ll feel it. Take a tick and let it crawl over your limbs. More than likely you’ll not feel a thing. No one knows how they do this, but I suspect that they charm our nerve endings, taming the cobralike neurons with the hypnotic music of their feet. The best way to detect a tick crawling up your leg is to notice a suspicious absence of tickling and itching. Walking in the forest in summer generates an endless stream of entomological creepies on your skin. When the stream of sensation dries, you’ve got a tick.

Unlike mosquitoes, ticks take their time about feeding. They press their mouthparts against the skin, then slowly saw into the flesh. Once this inelegant incision has opened a large enough hole in the skin, they lower a barbed tube, the hypostome, to draw out blood. A full meal takes days to extract, so ticks cement themselves into the skin to prevent the host from scratching them off. The cement is stronger than the tick’s own muscles, explaining why burning ticks with matches is futile. Ticks cannot pull out rapidly, even when their rear ends are on fire. Lone star ticks feed deeper than other species, making them particularly hard to remove.

The blood meal causes ticks to swell up so much that they grow new skin to accommodate their meal. They drink so much blood that they face a reversal of the dehydration problem of their questing days. Rather than curtail their meal when they are full, the ticks extract water from the blood in their gut, then spit it back into the host, an action that surely violates the spirit, if not the letter, of the laws of chivalry, particularly if the tick carries one of the many bacteria that cause disease. The half teaspoon of blood in a fully engorged tick is therefore
a distillation of several teaspoons of host blood, thickened and stored in the tick’s belly.

A feeding female adult tick will increase her body weight one hundred times, then summon her lovers from elsewhere on the host. She releases pheromones while still attached, and these airborne chemicals create a scramble of males toward her voluptuousness. Once a male arrives, the female releases more pheromones, and the male crawls under the swollen enormity of his immobile mate. He uses his mouthparts to insert a small package of sperm into a chink in the female’s armor and then leaves her to finish her meal. When she is fully sated, she dissolves the cement around her mouth and crawls, or drops, onto the ground. There, she slowly digests the blood and fills thousands of eggs with nutritious yolk. Like the mosquito, the mother tick uses blood to fuel her reproduction. When the eggs are ready, she lays them in clusters on the forest floor. Her quest is over, the Grail’s blood has been transubstantiated into the Body of Tick Egg, and she dies empty but fulfilled.

A week later the dreaded “seed ticks” emerge from the eggs. These larvae look and act like miniature versions of their parents as they swarm up the vegetation around their hatch site to begin their quest. Because they emerge in clusters, they attack hosts en masse, multiplying our misery. Only one in ten of these larvae succeeds in finding a host. Most starve or dry out before a suitable animal passes by. Lone star larvae attack birds, reptiles, and mammals except for rodents, which they seem to avoid. The larvae of other tick species reverse this preference and seek out mice and rats for their first meal. Successful larvae feed in the same way as adults, then drop off and molt into a slightly larger form called a nymph. The nymphs quest and feed, then molt into adults. The adult tick in the mandala has therefore already completed two successful quests. She may be two or three years old, having overwintered as a larva and then again as a nymph.

I am tempted to repeat my experiment with the mosquito and reward this tick’s longevity with a gift of my blood. I pass up the opportunity
for two reasons. First, my immune system reacts violently to tick bites, leaving me itching and, if I have more than a few bites, sleepless. Second, unlike with the mosquito, there is a fair chance that this tick is carrying a nasty disease. The most famous tick-borne malady, Lyme disease, is fairly rare here and is seldom carried by lone star ticks. However, lone star ticks are the primary carriers of other diseases including Ehrlichiosis and the mysterious “southern tick-associated rash illness.” These latter bacteria have yet to be propagated outside the human body, so we know very little about them, other than they cause a Lyme-like illness. Rocky Mountain spotted fever and malaria-like babesiosis also may lurk inside this lone star. This bestiary of pathogens is a powerful disincentive to offer myself.