One of Tschinkel’s graduate students, Sasha Mikheyev, analyzed 17 nest casts of Formica pallidafulva. She consistently found that when the descending tunnels are vertical, the adjoining chambers are round, and when the tunnels are inclined, the chambers are oval or teardrop-shaped and lined up along the tunnel’s axis. In a simple way, this observation illustrates one of the rules for how nests are built, Tschinkel says: If a tunnel is vertical, the ants doing the digging tend to distribute themselves evenly as they work, and if it is sloped, they tend to collect in the lower end.
That’s a start, but it’s still unknown which workers do the digging, whether they have this directional bias individually or as a group, or how the number of ants may influence nest size and shape. “I can imagine if there are only a few, they might dig only a tunnel, because they wouldn’t be crowded. But if there are more, they might dig chambers too,” Tschinkel says.
Months later, on an August morning, Tschinkel is deep in the Apalachicola National Forest with a whole new idea packed into the bed of a pickup truck. Over the years, Tschinkel has cast ant nests with latex, plaster of paris, and dental plaster enhanced with glass fibers. Each has advantages, but none is perfect. So today he’ll be trying something new: molten metal. He has spent months fabricating a clever foundry based on a kiln of fireclay in a galvanized garbage can and an air blower made from an auto heater fan.
Courtesy of the President and Fellows of Harvard University
Tschinkel sets up the works, piles in charcoal, lights it, and then waits an hour for 30 pounds of scrap zinc to melt. Meanwhile, he builds a mud dam around the entrance of a pogo nest and blows away loose sand through a plastic tube. Finally, he pours in the molten zinc. It flows so smoothly that Tschinkel worries it might be disappearing down a subterranean rat hole. After waiting 10 minutes for it to cool and harden, he starts digging beside the nest with his favorite shovel.
“It’s like buried treasure,” says Kevin Haight, a graduate student, as gleaming metal emerges from the ground. Bristling from some of the tunnels are hairlike projections, perfectly captured—the tunnels of another ant species, the tiny, sneaky thief ant Monomorium viridum, which survives by raiding the broods of other ant species. Haight ties a rope to the heavy cast and helps haul it out of the ground. It emerges in just eight pieces. “Fabulous,” Tschinkel says.
But later, when he has time to think about it, he concludes that zinc is too dense. The metal cools and sets up before it reaches the bottom of the nest. Next time, he says, he’ll make a first pour with molten aluminum and a second pour in zinc.
He has many opportunities to perfect his technique for making 3-D casts. There are 50 ground-nesting ant species in the area alone, and roughly 5,000 worldwide, each with its own unique way of life and shape of nest. For instance, there’s the genus Atta, the leaf cutter, which builds the world’s largest nests, up to 35 feet deep and covering as much surface as a small house. “I’d love to do an Atta nest,” Tschinkel says, smiling, “but I’d need several tons of plaster.”