On Trails by Robert Moor Page A

kind, called a vicious circle , like when a microphone is placed too close to an electronic amplifier, which allows minor sounds to self-amplify into those terrible, high-pitched shrieks familiar to any concertgoer. (Scientists used to poetically refer to the latter phenomenon as a “singing condition”; today, we simply call it feedback.)
    In the circling of tent caterpillars Bonnet and Fabre both witnessed, in a strikingly literal form, how the same mechanism that gives rise to a virtuous circle can also give rise to a vicious one. The animal psychologist T. C. Schneirla witnessed this grim transformation in 1936, while working at a laboratory on an island in the middle of the Panama Canal. One morning, the resident cook, Rosa, approached Schneirla in a state of feverish excitement. She led him outside, where he found, on the cement walkway in front of the library, hundreds of army ants marching in a circle about four inches across.
    Army ants, which are blind, rely heavily on pheromone trails to navigate the world. Most of the time, they march in thick raiding columns, consuming everything in their path, a habit that has garnered them the nickname “the Huns and Tartars of the insect world.” Schneirla could tell that something had clearly gone wrong with this colony. Instead of a marching column, the swarming mass resembled a ragged vinyl record, with concentric black rings spinning frantically around a hollow center. The circle widened as the day wore on. In the afternoon, rain began to drum the pavement, which divided the mass of ants into two smaller vortices, each rotating until nightfall. The next morning, Schneirla awoke to find that most of the ants had died; those that remained continued to plod in slow, tragic circles. A few hours later, all were dead, and other species of scavenging ants had arrived to carry them away.
    Schneirla was careful to point out that the doomed loop had most likely formed because the ants were walking on perfectly flat cement; otherwise, the undulations of the jungle floor might have disrupted it.However, looping trails had been recorded under different conditions by other prominent scientists, like the entomologist William Morton Wheeler, who once watched a group of ants circle the base of a glass jar for forty-six hours. (“I have never seen a more astonishing exhibition of the limitations of instinct,” he wrote.)
    In 1921 the explorer-naturalist William Beebe described running across a colony of army ants marching in an enormous circle through the Guyanese jungle. Beebe followed the procession for a quarter mile, under buildings and over logs, only to find that their trail ended where it began. Astounded, he traced the crooked circle again and again. The procession continued to circumambulate for at least a full day, “tired, hopeless, bewildered, idiotic and thoughtless to the last.” By the time that a few stragglers at last broke from it and wandered away, most had fallen dead from starvation, dehydration, or exhaustion.
    â€œThis peculiar calamity may be described as tragic in the classic meaning of the Greek drama,” wrote Schneirla. “It arises, like Nemesis, out of the very aspects of the ant’s nature which most plainly characterize its otherwise successful behavior.”
    Beebe was more succinct. “The masters of the jungle,” he wrote, “had become their own mental prey.”
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    There is a simple reason why we find the image of circling ants or caterpillars so troubling. The first instinct of humans who are lost in the wilderness is to cling to any trail they find and never leave it. Indeed, authorities on wilderness survival commonly recommend this tactic: “When you find a trail stay on it,” declares a backpacking guide published by the U.S. Forest Service, in a section titled “If You Get Lost.” A trail, the naturalist Ernest Ingersoll once wrote, is a “happy promise to the anxious heart