December 6th—Underground Bestiary
Our everyday experience of the animal kingdom is dominated by two groups of animals: the vertebrates and the insects. These two branches on the tree of life occupy most of our culture’s zoological field of vision, yet they represent just a fraction of the structural diversity of animals. Biologists divide the animal kingdom into thirty-five groups or phyla, each one defined by a distinctive body plan. The vertebrates and insects represent two subphyla among the thirty-five.
Why have the birds and the bees captured our imagination, leaving the nematodes, flatworms, and the rest of the world’s bestiary in a dusty back room of our consciousness? The simple answer is that we don’t run into nematodes very often. Or, we think we don’t. A deeper answer seeks to explain why the larger part of animal diversity is hidden from us. We get out and about enough, so why do we not run into our neighbors?
Unfortunately for the richness of our experience, we live in a strange and extreme corner of the world’s available habitat. The animals that we encounter are those few that also inhabit this unusual niche.
The first cause of our estrangement is our size. We are tens of thousands of times larger than most living creatures, therefore our senses are too dull to detect the citizens of Lilliput that crawl around and over us. Bacteria, protists, mites, and nematodes make their homes on the mountains of our bodies, hidden from us by the dislocation of scale. We live in the empiricist’s nightmare: there is a reality far beyond our perception. Our senses have failed us for millennia. Only when we mastered glass and were able to produce clear, polished lenses were we able to gaze through a microscope and finally realize the enormity of our former ignorance.
Our living on land further distances us from the rest of the animal kingdom, augmenting the handicap of gigantism. Nine-tenths of the animal kingdom’s main branches are found in water—in the sea, in freshwater streams and lakes, in watery crevices within the soil, or in the moist interiors of other animals. The desiccated exceptions include the terrestrial arthropods (mostly insects) and the minority of vertebrates that have hauled themselves onto land (most vertebrate species are fish, so terrestrial life is unusual even for a vertebrate). Evolution has plucked us out of our wet burrows, leaving our kin behind. Our world is therefore populated by extremists, giving us a distorted view of life’s true diversity.
My first dive into the soil helped me escape my strange ecological hermitage and gave me a taste of the treasury that lives below the surface. My thirst is whetted, so I dip down again. At three spots around the edge of the mandala I peel away a small clump of leaves, create a small hole in the litter, peer down with my hand lens, then replace the leaves. The contrast with the aboveground world is striking. Aboveground, apart from a passing titmouse, I seem to be alone in the forest. Yet animals abound an inch below the surface of the litter.
The largest animal in my foray is a salamander curled in the cup of a fallen oak leaf. The salamander would fit on my thumbnail but is hundreds of times larger than all the other animals that I encounter. This salamander is a crocodile among minnows, watched by a nearsighted whale.
As I peer closely through the hand lens, behind the salamander I see flickering movement and minute undulations on fungal strands and dead leaves. I strain my eyes until they ache, but I cannot identify the tiny animals that create these movements. I have reached a perceptual wall. Fortunately there is plenty to see on this side of the wall. The most common creatures are the springtails, or collembolans. If the mandala is typical of most terrestrial ecosystems, there may be up to a hundred thousand springtails within its borders. It is therefore not surprising that I find at least one of these tiny animals every time I lift a leaf. To the naked eye they are undefined flecks, but under the hand lens I can make out six stumpy legs protruding from the barrel-like body. All the individuals that I examine are doughy white and wet, with no eyes. These animated jellybeans are members of the onychiurid family of springtails. Their lack of pigment and blindness reflects the subterranean specialization of the group; unlike other springtails, these animals never wander aboveground. The onychiurids have lost the jumping organ, the furca, that gives springtails their name. Presumably a powerful belly-mounted catapult is of little use to an animal that spends its life in the soil’s crevices. Instead of springing away from predators, the onychiurids deter them by releasing noxious chemicals from glands on their skin. These chemicals ward off predatory mites and other common soil carnivores but are presumably less effective against the larger but less frequently encountered beaks of wrens and turkeys.
One hundred thousand springtails produce a lot of mini dung pats. The mandala contains a million springtail pellets, each one a miniature package of composted fungus or plant. The spores of bacteria and fungi pass through the gut undigested, so springtails act both as dispersers of the microbial community and as the soil’s champion compost makers. Springtails also exert an important effect at the other end of their digestive tracts. Although the details of this relationship are still unclear, springtails seem to enhance the mycorrhizal association between fungi and plant roots. They graze on fungal strands and thereby stimulate some fungi and suppress others. Springtails are like cows on a pasture, regulating the growth of their food by continuous clipping and by fertilizing the ground with their droppings.
The springtails’ central position in the life of the soil is, unfortunately, not reflected in their taxonomy. They have six legs, but their strange mouthparts (housed in a reversible pouch in the head) and distinctive DNA indicate that they are a sister group to the insects. Because they fall between the insects and the other invertebrates, the springtails are claimed by few biologists, and their lives are poorly known. But they are the evolutionary soil from which came the insect inhabitants of our aboveground world.
Springtails are the most numerous animals in my samples, but because springtail bodies are small, they account for less than five percent of the total weight of animals in forest soil. Relative to their ecological importance, springtails are also a species-poor group of animals. Six thousand springtail species grace the planet, compared to a million insect species (and over one hundred thousand species of fly). As I move around the mandala, I therefore encounter many springtails, all seemingly of the same type. The other animals that I find are different in each sample, reflecting their higher taxonomic diversity.
After the springtails, the next most abundant visible animals are other arthropods: spiders, gnats, and millipedes. The armored body plan of the arthropods has been modified by evolution into an engineer’s fantasy world of designs. Armor has been flattened into the wings of flies and sharpened into spider fangs. Jointed legs have been turned into silk-spinning tweezers, mushroom-munching mouthparts, and all-terrain climbing boots. No other group of animals rivals the arthropods in the diversity of body forms, yet all these forms are built on the same ground plan: a segmented outer case that is molted periodically to allow new growth.
The arthropod body plan is well represented in the mandala, but it is not the only one. Tiny snails graze among the dead leaves in the mandala’s soil. Some of these are juvenile versions of the larger snails that graze on the surface of the mandala, but other species spend their entire lives in the wet embrace of the litter. The snail’s shell is excellent armor but is simpler and less versatile than the arthropod’s all-encasing jointed suit. Because snails don’t molt, they cannot fully enclose their body within the shell. Snails are therefore vulnerable to attack through their shells’ openings. Many of the mandala’s snails have reduced this risk by partly barring their shell’s mouth with toothlike extensions to the shell’s lip. Some of these extensions are so well developed that there is little room for the snail’s body to squeeze between them as the fleshy part of the animal pokes out of the shell to feed.
Snails owe their success to the clever ways they use their tongues. They are the world’s most successful lickers—few surfaces on the planet escape their attention. The tongue
, the radula, is a toothy strap that the snail pokes out, then scrapes back, rasping whatever is below. As the radula moves back into the mouth it passes over a stiff lower lip, causing the radula to fold back and the teeth to bristle up. Each tooth is a bulldozer blade that gouges into the surface below, shoveling food into the mouth. This cross between a conveyor belt and carpenter’s plane is the key that unlocks the world for snails. We look at a boulder and see bare rock; snails experience a film of butter and jelly spread over the boulder’s surface.
As I continue my subterranean dive, I find yet another body form, the “worm.” Some of these worms appear familiar—the segmented earthworms and diminutive relatives of earthworms, the enchytraeids, or potworms. But my attention rests on these familiar figures for a few seconds, then is drawn to another, stranger worm that rests on the torn edge of a leaf. This animal is visible only through my hand lens and sits in the film of water that covers the leaf. As I watch, the worm rears up and thrashes in the air, then falls back into the water. The lurching motion identifies the worm as a nematode. Unlike the earthworms and potworms, this animal has no body segments, and its head and tail taper to points. There may be a billion nematodes in the mandala, most of them so small that only a strong microscope can reveal them. Some are parasitic, some are free-ranging predators, others graze on plants and fungi. Only the arthropods have more diverse feeding styles and ecological roles. Yet because nematodes are so small and water-loving, they live in scientific obscurity. The few people who do study these worms boast that if all matter were removed from the universe, leaving only nematodes, the planet’s shape would remain, a haze of worms. The forms of animals, plants, and fungi would still be discernible in the creamy fog and, because nematodes are so specialized, the original inhabitants of these forms would still be identifiable. Tell me what worms you have and I’ll tell you who you are.
My foray into the upper surface of the mandala’s soil has revealed more diversity of animal body designs than could be found in all of a zoo’s displays. Multitudes crawl, squirm, and writhe below my feet. But I seem to be alone up here in the air above the mandala. The soil’s warmth and moistness help make possible the zoological extravagance, but these benign conditions would be for naught if the soil were not well provisioned. Death is the soil’s main supplier of food. All terrestrial animals, leaves, dust particles, droppings, tree trunks, mushroom caps, are destined for the soil. We are all destined to pass through the dark underworld, feeding other creatures as we go. The human economy has no counterpart to the soil’s all-embracing monopoly. Some segments of our economy have more power than others, but nowhere does any one industry get to process and profit from the work of all the others. Banks come close, but the cash economy bypasses them. In nature, however, there is no escape from Isaiah’s prophecy; “their root shall moulder away, and their shoots vanish like dust.” Decomposers and their business partners fill the soil with their lively and varied activities. The seeming dominance of the aboveground world is therefore an illusion. At least half the world’s activity is belowground.
In the end, it is not just the diversity of the bestiary that our size and dryness hides from us but the true nature of life’s physiology. We are bulky ornaments on life’s skin, riding the surface, only dimly aware of the microscopic multitudes that make up the rest of the body. Peering below the mandala’s surface is like resting lightly on the body’s skin, feeling the pulse move.
December 26th—Treetops
It is midday and the sky is clear, but no sun shines on the mandala. The slope here is tilted northeast, away from the low sun, and the bluff uphill blocks direct sunlight. Slanting rays clear the bluff and illuminate treetops, creating a divide between light and shadow that cuts trees at twelve feet from the ground. This divide will sink day by day until the sun is high enough, in February, to kiss the ground again after a long absence.
Four gray squirrels loaf in the bright upper branches of a dead shagbark hickory tree fifty meters down the slope. I watch them for an hour, and mostly they loll in the sun, limbs sprawled. They seem companionable, sporadically nibbling the fur on one another’s hind legs or tails. Occasionally one will break from sunbathing and chew the fungus-encrusted dead branches, then return to sit silently with the other squirrels.
This scene of sciurid tranquillity makes me unaccountably delighted. Perhaps I so often see and hear squabbling among the squirrels that today’s ease seems particularly sweet. But something more is behind my delight; I feel freed from some burden carried by my overtrained mind. Wild animals enjoying one another and taking pleasure in their world is so immediate and so real, yet this reality is utterly absent from textbooks and academic papers about animals and ecology. There is a truth revealed here, absurd in its simplicity.
This insight is not that science is wrong or bad. On the contrary: science, done well, deepens our intimacy with the world. But there is a danger in an exclusively scientific way of thinking. The forest is turned into a diagram; animals become mere mechanisms; nature’s workings become clever graphs. Today’s conviviality of squirrels seems a refutation of such narrowness. Nature is not a machine. These animals feel. They are alive; they are our cousins, with the shared experience that kinship implies.
And they appear to enjoy the sun, a phenomenon that occurs nowhere in the curriculum of modern biology.
Sadly, modern science is too often unable or unwilling to visualize or feel what others experience. Certainly science’s “objective” gambit can be helpful in understanding parts of nature and in freeing us from some cultural preconceptions. Our modern scientific taste for dispassion when analyzing animal behavior formed in reaction to the Victorian naturalists and their predecessors who saw all nature as an allegory confirming their cultural values. But a gambit is just an opening move, not a coherent vision of the whole game. Science’s objectivity sheds some assumptions but takes on others that, dressed up in academic rigor, can produce hubris and callousness about the world. The danger comes when we confuse the limited scope of our scientific methods with the true scope of the world. It may be useful or expedient to describe nature as a flow diagram or an animal as a machine, but such utility should not be confused with a confirmation that our limiting assumptions reflect the shape of the world.
Not coincidentally, the hubris of narrowly applied science serves the needs of the industrial economy. Machines are bought, sold, and discarded; joyful cousins are not. Two days ago, on Christmas Eve, the U.S. Forest Service opened to commercial logging three hundred thousand acres of old growth in the Tongass National Forest, more than a billion square-meter mandalas. Arrows moved on a flowchart, graphs of quantified timber shifted. Modern forest science integrated seamlessly with global commodity markets—language and values needed no translation.
Scientific models and metaphors of machines are helpful but limited. They cannot tell us all that we need to know. What lies beyond the theories we impose on nature? This year I have tried to put down scientific tools and to listen: to come to nature without a hypothesis, without a scheme for data extraction, without a lesson plan to convey answers to students, without machines and probes. I have glimpsed how rich science is but simultaneously how limited in scope and in spirit. It is unfortunate that the practice of listening generally has no place in the formal training of scientists. In this absence science needlessly fails. We are poorer for this, and possibly more hurtful. What Christmas Eve gifts might a listening culture give its forests?
What was the insight that brushed past me as the squirrels basked? It was not to turn away from science. My experience of animals is richer for knowing their stories, and science is a powerful way to deepen this understanding. Rather, I realized that all stories are partly wrapped in fiction—the fiction of simplifying assumptions, of cultural myopia and of storytellers’ pride. I learned to revel in the stories but not to mistake them for the bright, ineffable nature of the world.
December 31st—Watching
The weak sun of late afte
rnoon shines on the westward facing slope of the other side the valley. The red-tinged light reflects from the bark of massed trees, giving the forest a purple-gray glow. As the sun falls, a line of shadow swings up the slope, extinguishing the warm reflection, turning the forest to dusky brown. As the sun drops lower, its rays angle into the sky, over the mountain. Crimson shades into haze on the horizon, and the sky’s blue fades, first to watery mauve, then to gray.
Ten days ago, on the day of the winter solstice, I watched this same swing of sunlight. The rising border between dark and light on the opposite forest slope drew all my attention, its climb up the mountain building to the moment when the shadow would crest and the bright sunlight would blink out. At the very instant that the line of shadow hit the horizon, coyotes hidden on the forest slope just to my east broke into howls. They yipped and wailed for half a minute, then fell silent. The timing of their chorus seemed too precise to be a coincidence, coming as it did at the moment that the sun slipped off the slope. We may both, coyote and human, have watched the bright spectacle on the mountainside and been stirred by the sight of the sun’s disappearance. Coyotes’ howling behavior is known to be sensitive to both daylight and to the moon’s phase, so it is not unreasonable to suppose that these animals might sometimes wail to the setting sun.
The Forest Unseen: A Year's Watch in Nature Page 24
