Sex on Six Legs_ Lessons on Life, Love, and Language From the Insect World - Marlene Zuk [81]
Army ants occur in several parts of the world, including the southern and western United States, but have been best studied in the New World tropics. They lack a fixed nest site, instead creating bivouacs, football-shaped masses that can be nearly a yard wide with anywhere from ten thousand to seventy thousand workers surrounding the queen and larvae, depending on the species. Hölldobler and Wilson estimate that the bivouac contains "a kilogram of ant flesh." The ants link their limbs and jaws to form their shelter, making a kind of savage yet delicate lacework of individuals that supports layers upon layers of brownish bodies. Just after dawn breaks, the bivouac seethes and breaks apart, sending out lines of ants in many directions.
The lines include army ant workers of several shapes and sizes, all female, of course, despite my students' disbelief. The small and medium-sized individuals lay down an odor trail as they walk down the middle of the track, while the larger soldier caste ants, with their scimitar-shaped jaws, lumber alongside. Workers are about the size of many North American ants, perhaps as long as a grain of rice, but the soldiers are three times their size, about as long as a kidney bean. The streams of advancing ants have no leader; individuals hustle back and forth at the edges of the swarm, altering direction as they encounter prey.
As my childhood reading experience suggested, army ants and their relatives the African driver ants are merciless when they encounter an animal in their path. People and other vertebrates such as birds or squirrels, however, are usually able to evade the advancing columns unless they are injured or otherwise prevented from moving out of the way, which vindicates at least some of my teacher's skepticism, though the ants certainly could overpower an immobile human being. Insects, spiders, and other invertebrates usually cannot escape so easily and are surrounded by the eager jaws of the horde. Hundreds of ants sink their mandibles into the prey, their grip so strong that if the ant is torn away, its jaws remain imbedded in the flesh of its victim. Anecdotally, at least, this powerful grasp has led to their use as sutures by the Masai of Africa, who induce the ants to latch onto either side of a wound with their jaws, holding it shut even after the body of the ant is discarded. (I was once asked how the ant jaws are removed once they have served their purpose, and I don't know the answer, save that the process might put that "ouch" at the tug of a Band-Aid to shame.) Small animals are borne away intact, while larger victims such as tarantulas or grasshoppers, or the occasional unlucky mouse or even deer, are efficiently butchered and carried off in chunks that can be managed by one of the medium-sized workers.
The intimidating-looking jaws of the soldiers, like many weapons, are not actually useful for practical tasks, and so all of the work of hauling food back and forth is done by the more modestly equipped smaller workers. Sometimes a group of such ants collaborates to transport a larger prey item, balancing it expertly among themselves so that the load can be carried by the minimum number of individuals needed. Schneirla reported that the entire operation is accompanied by the sound of thousands of tiny exoskeletons tapping against the dry leaves of the forest floor, a sound that according to Hölldobler and Wilson "beats on the ears of an observer until it acquires a distinctive meaning almost as the collective