Threads from the Web of Life: Stories in Natural History

The Living Wood

3 The Living Wood WHAT is it in the twilight that brings the air alive? Why is a walk down the earlier afternoon’s path so different when the day is fading? As the hush of evening falls over the hollows on either side, our senses heighten, straining to fill in what is lost to sight. The color drains from the flowers, now folding up against the darkness; the stream begins to shimmer with rippled beads of reflected moonlight. The butterflies and birds have retired , but the open spaces in the understory have awakened with the silent fliers of the night. The most prevalent of these unseen motes in the air are the micromoths. Most of them are smaller than the silken parachutes that buoy dandelion seeds floating on the breeze. Their tiny wings move them through the night at a pace slower than our walking speed. Nonetheless, should we walk through their flight path, we would never feel them collide with us—they brush on past our faces or fingertips, surfing to the side on the thin wave of air displaced by our forward motion. Field guides describe the large silk moths, such as the Polyphemus and the Luna; they describe the flashy tiger moths and the hummingbird-like sphinx moths. But the micromoths are not portrayed in field guides; they have no common names, and, in flight, they all look alike. They are smaller than the smallest butterfly and too slow of wing to escape the diurnal wood warblers and flycatchers, so they take flight only in complete darkness, where they will not attract attention. If disturbed during their daylong rest they would choose to drop like a scrap of dead leaf rather than fly. Nonetheless, their humble stature has its advantages. When they collide with spider web, it is only with a single strand; they leave a few powdery scales stuck to the silk and continue on their 3 Threads from the Web of Life way. They need very little sustenance to prosper and so can proliferate in the most insubstantial of niches. They exist in myriad forms, with as many different species as there are different microhabitats in the forest. Every space in the living wood is home to one micromoth or another—everywhere you look, though you may not see them, every place you put your hand—on the trunk of the tree, there are scores of micromoth niches; on the ground, scores more. Multiple, sequential micromoth habitats exist even on a single, tough live oak leaf. When that leaf is first produced early in the spring, it is home to a micromoth larva—a leaf miner. This flattened caterpillar moves in two-dimensional space through its paper-thin domain, tunneling steadily until high summer darkens the leaf with tannins too toxic to feed upon. When the leaves are shed, brown and etched with the fading traceries of the early season miners, another micromoth is waiting on the ground for them, a forager on oak deadfall. Beneath the layer of fallen leaves there lives a third micromoth species with another unique specialization, feeding on the leaves that fell last year and that are by now flattened to detritus by the intervening winter. Farther down still lives yet another species that feeds on the fungus growing on the disintegrating leaves from the year before that. The number of different species of micromoth larvae that feed on the resources provided by a single type of plant, multiplied by the total number of tree, shrub, and annual flower types in the forest, begins to estimate the total count of micromoth species in a particular stretch of wildland. And these myriad niches are divisible into more again by the succession of specialist micromoths adapted to occupy each one under different circumstances: different months, or exposures, or plant varieties. The micro-habitats diversify with every foot of descent from the ridge crests down toward the riparian bottomlands. As soon as we measure the dimensions of yet another miniscule subdivision in the forest, and look into that newly described niche, we find the micromoth that lives there. One way to comprehend the diversity of these woodland habitats would be to census all the different micromoth adults hovering in every glade, beneath each dark thicket, across the forest. But these nocturnal sprites are not easily counted. Many 40 Threads from the Web of Life of them may live for generations...