By Walter R. Tschinkel
Nest size varies enormously from species to species. Eastern woodlands Aphaenogaster ants make twenty-inch-deep nests occupied by a few hundred workers. New World tropical leafcutter ants create colossal underground metropolises, each housing several million workers that tend huge fungus gardens. Every ant species constructs a nest so distinctive that an entomologist can usually tell which one created it.
Florida's coastal plains are ideal for studying the ants' subterranean architecture: the deep, homogeneous sand is a congenial medium both for the ants and for the researcher seeking a permanent record of these ant cities. After practicing on examples of modest size, I decided to tackle the abandoned dwelling of a particularly ambitious nest-building species: the Florida harvester ant. The nest (pictured opposite) contains 135 chambers arranged along four vertical connecting tunnels that total thirty feet in length. Some of the chambers are specialized for food storage; this nest held about a quarter of a million seeds collected by workers for later consumption. The colony that had built and occupied this nest began with a queen that left her home and mated with another colony's male. After digging a narrow, twelve-inch-deep chamber, she sealed herself inside, laid her first few dozen eggs (a single mating provides the queen with a lifetime supply of sperm), and then reared the hatched larvae and pupae with nutrients stored in her body. These pupae emerged as workers, which then reared more workers, and as the colony grew, the ants deepened the nest and added more chambers. A large harvester ant nest may be as deep as ten feet and contain as many as 200 chambers.
Once or twice a year, the colony abandons its home and excavates a new onea formidable task that in the case of the nest shown here was completed in four or five days by about 5,000 workers. Together they weighed a total of seven-tenths of an ounce and moved forty-four pounds of sand. Within such nests, the living inhabitants arrange themselves more or less according to their stage of life. Larvae and pupae live in the bottom third, where they grow into young adult workers that will care for the brood of eggs and larvae surrounding them. As the workers grow older, they gradually drift upward, changing their occupation from brood care to more general duties, such as transporting seeds and maintaining the food-storage chambers. Later they take up residence near the surface, where they become the colony's defenders and spend the last quarter of their one-to-two-year lives venturing outside to forage for seeds and insects.
In spring the colony breeds some winged males and unmated queens that will, in time, seek mates outside the colony. During their age-related upward migration, the workers become more and more active in excavating chambers to hold the growing population and its food supply, which is why the nest has a top-heavy shape. The ants' social organization helps shape the space in which they live, and the space in turn organizes the colony by providing separate areas and chambers for various activities and functions. Harvester ant colonies thus have four dimensionsthe usual three dimensions of space and the vertical dimension of worker age.
Born during World War II in the Sudetenland region of Czechoslovakia, Waiter R. Tschinkel grew up in Texas, Alabama, and Connecticut. After attending Wesleyan University, he earned his doctorate in biochemistry at the University of California, Berkeley, with a thesis on chemical communication in beetles. He enjoys digging holes and can excavate a hundred cubic feet of earth in about an houran avocation that suits his passion for casting ants nests in plaster. Tschinkel is currently the Menzel Professor of Biological Science at Florida State University, where for thirty years he has conducted research on how ants manage to function as a superorganism. He has published more than sixty scientific papers on the social biology of ants.