“That’s Polybia liliacea,” he said. “Really aggressive social wasps.” He took pictures while I admired the paper walls of the wasps’ citadel, striped in alternating ribbons of cinnamon, rufous, and chestnut brown, and studded with thousands of small black wasps—an army of defenders poised to take all comers. It was hard to believe that creatures so tiny could build a structure of such size and perfection, or that it could support its own weight without collapsing into the river.
