Across the vast plains of southern South America, a chubby rodent reigns underground in a vibrant, hierarchical world. The plains viscacha, a stout cousin of the chinchilla, builds subterranean “cities” known as “vizcacheras,” where up to 50 individuals live together. With tunnels reaching 10 feet (3 meters) deep, these complex networks of dark chambers and hidden entrances fascinated Charles Darwin during his 19th-century travels through the region.

These underground engineers are thought to live up to eight years. These animals are organized into complex colonies and guided, in part, by the vizcachón — the oldest and most experienced male — who signals the all-clear each evening. As dusk falls, the vizcachón is the first to emerge as a lookout. If all is calm, he gives the signal, and the rest of the group follows.