1.6 million people live within the 60 square kilometers of Manhattan Island—the densest population center in the United States. Compared to such congestion, nature is supposed to be slow and uncrowded. Yet a single square meter of soil in the boondocks—less than a billionth the area of Manhattan—holds a thousand times more animals than all Manhattan holds humans. Earthworms, beetles, mites, ants, nematodes, springtails, and protozoa bump cell walls and brush antennae as they cram the intricate grids of dark dirt streets. Unlike our human cities which end at rivers or peter into suburbs, this great clay underground metropolis spreads vastly across every continent of earth, diminished only by deserts and ice caps. There is nothing rural about nature.