The Forest Unseen: A Year's Watch in Nature (22 page)

The katydid’s file and plectrum do not work alone. The secret of the katydids’ loudness is a patch on the wing that acts like the skin of a banjo, resonating and amplifying the plectrum’s vibrations. This skin is tightened such that its resonant tone is different from the note produced by the file. These mismatched tunings produce a clash of vibrations that combine to make the katydid’s dissonant buzz. Crickets, unlike their katydid cousins, have skins tuned perfectly to their files, allowing them to sing sweet notes unsullied by harsh side tones.

Like those of humans and many birds, katydid songs come in regional dialects. Northern and midwestern katydids sing slowly and with two or three syllables.
Ka-ty, Ka-ty-did, she did-n’t.
Southerners add more syllables and sing much faster.
Ka-ty-did-n’t, she-did-n’t, did-she, ka-ty-did.
In the West, katydids sing slowly and with just one or two syllables.
Ka-ty, did, did, ka-ty
. Katy’s story evidently has many interpretations. The function or consequences of these regional accents is unknown. Perhaps dialects adapt the songs to the acoustic properties of different forests? Or maybe they reflect hidden differences in the preferences of females in different regions, differences that may inhibit crossbreeding between populations with different ecological adaptations?

The katydid chorus is punctuated by brief, dying bursts from
cicadas. Cicadas are singers of blazing hot afternoons, and they relinquish their acoustic dominance as dusk advances. The cicadas’ drawn-out whine comes from an apparatus that is stranger yet than the katydid’s plectrum, ridge, and drum. On each side of the cicada’s body sit discs embedded in the hard external skeleton. The discs look like closely barred porthole windows. The bars are stiff struts that can snap back and forth sideways. When a muscle pulls on the disc, the struts snap in a cascade, producing a trill, then each strut pops back as the muscle is relaxed. The sound of every snap and pop is amplified by membranes and an air-filled sac inside the cicada’s body. These corrugated discs, called tymbals, are unique in the animal world.

Both cicadas and katydids derive their energy from plants. Cicada larvae are subterranean tree parasites, sucking tree sap from roots, living like moles with syringes. Unlike the rapidly growing katydids, young cicadas take several years to mature. Tonight’s cicada chorus is therefore fueled by four or more years of tree juice, sung by moles that have crawled from their burrows and taken to the trees.

Female katydids and cicadas wander the treetops, contributing no sound of their own but listening to the chorus of males. Katydids hear with nerves on their legs; cicadas have ears lodged in their abdomens. If the male singers are loud or snappy enough to lead the chorus, the listener will move closer, listen some more, then mate.

When female and male katydids entwine, he passes to her not only a small sac of sperm but a large “nuptial gift” of food. This food sac is usually about one-fifth the male’s body weight. The manufacture of the sac is so taxing that the male’s abdomen is mostly filled with food sac glands. The function of the gift varies from species to species. In some katydids the male is providing food with which the female will produce eggs. In other species, the gift prolongs the female’s life span.

Unfortunately for singing male katydids, potential mates are not the only listeners in the forest. Singing undoubtedly increases the risk of being discovered by a bird. Cuckoos, in particular, are fond of hunting katydids. But the most abundant and dangerous enemy of songster
katydids are tachinid flies. These spiny beasts feed on nectar as adults, but their larvae are parasites of other insects. Several tachinid species specialize in katydids and have ears tuned specifically to the song of their preferred host. The eavesdropping mother fly homes in on her prey, lands close by, then deposits a brood of writhing larvae. The larvae swarm onto the victim and burrow into his body. Like ichneumon wasps inside a caterpillar, the fly larvae slowly consume the katydid from the inside out. The hit-and-run strategy of mother flies is guided solely by sound, so tachinid parasitism is a burden carried almost exclusively by male katydids.

Darkness advances. The cicadas finally fall silent, ceding the chorus until tomorrow, when the day’s heat will wake them. Other katydid species join in. Lesser angle-wing katydids shake out bursts of raspy sound, like arboreal maracas. Whines and buzzes from other species poke out from the chorus, hinting at the diversity of leaf chewers above.

As dusk progresses my sense of sight fails, and the forest swells around me in dark billows that finally merge into blackness.

Only the forest’s exultant thunder remains:
CHA CHA! CHA CHA!

I
feel a powerful sense of delight in the morning’s strong sun. My spirits were lifted by the sight of a dozen migrant warblers bathing in the stream that crosses my path to the mandala. They stood in shallow stream pools, dipping and shaking their bodies, feathers fluffed out. Each bird raised a halo of silvery flashing water drops. They seemed to baptize themselves with sunlight.

The birds’ unrestrained enjoyment gave me particular gratification, because this same stream was the source of much recent trouble. Two days ago, on my walk from the mandala, I found the stream ransacked, every rock turned over or thrown aside. This had happened before, poachers coming through and grabbing every salamander they could, hauling them away for use as bait. The stream was gutted. The forest’s salamanders would die on hooks or in stinking bait buckets. I felt disgust and visceral anger. I walked on, my ire surging and coiling into itself. Up the hillside I marched, mind wound tight. When I reached the base of the cliff, the tension snapped and unwound: my heart kicked and started fibrillating, the beats coming in uncountable squalls.

There followed a difficult bike ride into town, a few hours in the hospital with IVs and drugs. Within a couple of hours, my heart settled back down and, after a day of rest, I’ve returned to the forest. Today, the warblers’ glistening beauty therefore seems particularly sweet, perhaps even redeeming.

At the mandala, I see the plants with new eyes. In addition to the ecological community, I now see a pharmacopoeia. This new way of seeing came to me with the drugs I was given at the hospital, both of which were derived from plants. Aspirin, originally from willow bark and meadowsweet leaves, slipped into my cells and, like the chemicals in mosquito and tick bites, disabled the processes that cause clotting of blood. Digitalis, from foxglove leaves, bound to my heart’s cells, shifting the chemical balance, making my heartbeat stronger, surer.

In the hospital room, I first felt separated from nature, but this was an illusion. Nature’s tendrils penetrated the room, reaching out to me through pills. Plants twined inside me, their molecules finding and grasping mine in a close embrace. Now I see these connections at the mandala: every species brims with medicinal potential. Willow, meadowsweet, and foxglove do not grow here, but the mandala’s plants have their own healing properties.

Mayapple is one of the more common plants on this mountainside, and its umbrella-like leaves poke up from several places in the mandala. The ankle-high leaves of mayapple grow from underground stems on the forest floor. The stems grow horizontally, branching through the leaf litter, gradually expanding until dozens of leaves grow in a patch that can be several meters across. Native Americans have long known that the plant has powerful properties. At very low doses, extracts from the plant were used as laxatives and to kill intestinal worms; higher doses, which would be fatal if ingested by people, were put onto newly sown corn to protect the seed from crows and insects.

Modern studies of mayapple have found that the plants’ chemicals can kill viruses and cancer cells. Mayapple extract is now used in creams that heal warts caused by viruses and, after the extract has been chemically modified in the lab, as chemotherapy against cancer. These drugs could obviously not exist without mayapple. Less obvious is their dependence on other members of the forest community. Bumblebees pollinate the flowers of mayapples, flying under the leaves to reach the nodding white blooms. Later in the summer, the flowers mature into
small yellow fruits, each about the size of a small lemon, the “apples” for which the plant is named. Box turtles have an unusual affinity for these mature fruits, sniffing them out, devouring them, and then wandering away with a bellyful of mayapple seeds. Without passage through the gut of a turtle, the seeds generally cannot germinate. Pharmaceutical textbooks do not discuss the ecology of forest-dwelling bumblebees and turtles, but the practice of medicine needs these species nonetheless.

Wild yam is another local species with important medicinal properties. It is not found within the mandala’s circle but grows scattered all around, particularly in wetter, shady patches of forest. Yam grows as a vine, wrapping its thin stem around shrubs and small trees as it climbs to head height or above. The stem and heart-shaped leaves are delicate and do not survive hard freezes, so the plant overwinters as fingerlike tubers under the leaf litter. These tubers are rich in chemicals that are structurally similar to human hormones, including progesterone. This fact was not lost on Native Americans, who used the plant to relieve the pains of childbirth. Later, in the 1960s, the first birth control pills were made by chemically modifying extracts from the tubers. Yams are also reported to lower cholesterol, reduce osteoporosis, and relieve asthma, although the evidence for these properties is debated.

Mayapple and yam are easy to find in this forest. Another wild medicinal species, ginseng, is unfortunately not so common. Its fate offers a caution about the overharvesting of useful wild plants. The human appetite for ginseng’s stimulative and healing properties is so strong that most of eastern North America has been stripped of this once abundant forest herb. In the mid-nineteenth century, the United States annually exported between one-half and three-quarters of a million pounds of ginseng. Similar quantities may have been used domestically. Now, the annual export is less than a tenth of what it was, driven down by the rarity of the plant. Despite regulation of the ginseng harvest by the federal and state governments, the market for “sang,” as it is known locally, is thriving. A few miles down the road from the mandala,
dealers set up seasonal stalls at major road intersections and buy roots from local “diggers.” Dried roots fetch five hundred dollars or more per pound, a price that provides strong motivation to search for new plants. For skilled diggers, the harvest provides a significant economic opportunity in an otherwise difficult local economy.

The decline in ginseng’s abundance has induced some forward-looking dealers and diggers to start cultivating semiwild populations of ginseng by sowing seed in the forest as they hunt for roots. Like box turtles transporting mayapple seeds, humans have now taken on the role of seed dispersers. This task was previously performed by birds, especially thrushes, that regard ginseng’s ruby berries as a tasty late summer snack. Fortunately for the human sowers, ginseng seeds are less fussy than those of mayapple and will germinate without passage through a bird gut. Whether these sowing efforts can protect ginseng from further declines is presently unknown; most botanists remain very concerned for the species’ future.

Ginseng, yam, and mayapple are all small plants that overwinter as nutritious underground stems or roots. This shared way of living explains why they are all so rich in medicinal chemicals. Unlike fast-moving animals or thick-barked trees, these stationary, thin-skinned plants are highly vulnerable to attack from mammals and insects. Their underground stores of food are particularly attractive to would-be predators. Because they lack the ability to flee or to hide behind strong walls, the plants’ only defensive option is to soak their bodies in chemicals that play havoc with the guts, nerves, and hormones of their enemies. Because natural selection has designed the defensive chemicals specifically to attack the physiology of animals, these poisons can, in careful human hands, be turned into medicines. By finding just the right dose, herbalists can turn the plants’ defensive arsenal into an impressive collection of stimulants, purgatives, blood thinners, hormones, and other medicines.

The mandala’s medicinal plants and the drugs in my bloodstream are representatives of a much larger group: one-quarter of all prescriptions
are filled with medicines derived directly from plants, fungi, and other living organisms. Many of the remaining prescriptions involve modifications of chemicals originally found in wild species. But the complex chemical world of the mandala’s species is poorly understood. Of the thousands of molecules in the two dozen plant species visible in the mandala, only a handful have been thoroughly investigated in the laboratory. Others have yet to be examined, despite their use in traditional herbal medicine. The invisible biochemical diversity of the mandala is full of potential that awaits exploration.

My experience with botanical medicines has taught me that my kinship with the mandala’s inhabitants extends all the way to the tiny scale of molecules. Previously, my kinship primarily meant shared genealogy on an evolutionary tree and interconnected ecological relationships. Now I understand how intimately my physical being is tied into the community of life. Through the ancient biochemical struggle between plants and animals, I am bound to the forest through the architecture of my molecules.

M
igrating warblers eddy through the mandala’s trees, washing through branches in waves. A Tennessee warbler, returning from its breeding grounds in the northern forest, drops to a low maple sapling at the mandala’s edge and probes the leaves in search of food. The bird has another two thousand miles to fly before it reaches its winter home in southern Central America. Feeding is an urgent concern.

The state of the leaves above the mandala hints at the source of the warbler’s meals. Each leaf has been shotgunned, leaving ten or more ragged holes. Most leaves have lost nearly half their surface area. The mandala’s caterpillars have turned summer leaves into insect flesh. This flesh will, in turn, fuel the warblers’ long journey.