noticeable to a human being but were daunting to a ten-millimeter-long ant. In the miniature world of antdom, clumps of grass were like groves of trees and bushes, and dead leaves and twigs like fallen timber. A surface of sand smooth to humans was to the ants a jumble of rocks, and pebbles were large boulders. Rain was a deadly threat. One drop striking an ant had the human-equivalent force of a firehose jet. A rivulet of rainwater trickling through a crease in the soil was the equivalent of a flash flood raging down a desert ravine.
As the elite ant left on her journey, she remembered the route more or less precisely. She had been to the Trailhead territory before, and remembered the way. She carried a compass in her head, using the sun as a lodestar. This reliance could have been the source of a huge error for an ant, because the sun travels across the sky and so the correct angle constantly changes. However, each ant also carried in her head a biological clock set on a full day's twenty-four-hour cycle, run with a precision far beyond the capacity of an unaided human brain. Using her clock, the scout continuously changed the angle to the sun needed to keep her on track.
The trajectory of the sun by itself is completely reliable in space and time. At Nokobee it traced a geometrically perfect arc across the sky, rising through the pines on the eastern lakeshore, passing directly above the anthills of Dead Owl Cove, and finally disappearing westward into the forest lying beyond. The azimuth read by the ant, however, unlike the transit of the sun, was less than perfect. So the scout occasionally stopped and gazed at prominent features she had memorized during earlier trips. A pair of pine seedlings were one such signpost, a circular opening in the canopy a second, a dark shadow beneath a holly shrub a third.
Then there was the odor terrain, parts of which the scout memorized from chemical cues she had encountered on earlier trips. In exercising this ability, she was as different from a human being as it is possible to imagine. The scout smelled the ground continuously and precisely as its surface rushed by two millimeters' distance beneath her body. Her nose was the outer segments of her paired antennae--the two feelers on her head. She turned these hypersensitive instruments downward, enough to almost touch the ground, and swung them from side to side. The odors she detected as she ran, specific in their mix, intensity, and gradient, provided detailed information of her location and direction of travel. They were her combined field guide and topographic map.
The nearby pine-leaf litter conveyed its acrid scent to mingle with that from the humus beneath the colony foraging grounds. A surge of one particular blend greeted her here, a countersurge of another kind there. The prevailing background was overpowered now and then by a flashing scent of something radically different--quickly gone but remembered for a while.
The olfactory world of the running Streamsider contained much more than an invisible road map. Bombarding the ant from below and from all sides above were the odors of organisms that inhabited the soil--so densely as to make up a large part of the physical bulk of the soil. There were endless local profusions of fungal hyphae and bacteria. Each gave up its signature smell. There were the rising odors of the animals the size of the ant or smaller, a quarter million packed into every square meter. They were the insects, spiders, pillbugs, nematode roundworms, and other invertebrates that dominate in numbers. One trace within the mix picked up by the sweeping antennae could disclose a potential prey, another a waiting spider or some other ambush predator.
The human mind cannot imagine the tumult of chemical stimuli by which such a traveling ant guides every moment in her life, and thus survives. It cannot conceive of the constant enormity of the deadly risks she must skillfully evade, instantaneously at every moment.
The Streamsider scout hurried undistracted through this olfactory cosmos. Her destination was in the direction of the enemy nest but not the nest itself. She was consciously headed for a flat, open area half the distance there. On arriving, the scout mingled with a group of nestmates who had preceded her, and--an extraordinary event for ants--they also mingled freely with scouts from the Trailhead Colony. One of these enemies was the newly arrived elite and former Trailhead Queen