New research recently published in the Journal of Archaeological Science reveals a key—albeit seemingly unlikely—indicator for the health of the Inca Empire: llama droppings. Led by paleoecologist Alex Chepstow-Lusty of the University of Sussex, a group of researchers has been able to accurately track the rise and fall of the Incan Empire by examining the oribatid mite population in Marcacocha, tiny spider relatives that once gorged on the feces of llamas passing through the region. Now a dried-up wetland in the mountains, Marcachoca was a small lake over 200 years ago, and a popular rest stop for Incan llama caravans on their way to and from the ancient city of Ollantaytambo. Thousands of llamas carrying trade goods like maize, salt, feathers, and coca leaves would descend upon Lake Marcacocha, where they would water themselves, drink, and defecate along the edges of the pool. Washed into the lake, their dung was then consumed by the resident, half-millimeter long mites. When the mites died, they sank into the lake mud, preserving their corpses and allowing Alex Chepstow-Lusty to discover them in a sediment core centuries later. Of course, the more llamas that passed through Marcacocha, the more poop the mites had to eat and thus the larger their populations could grow. Conversely, a decline in the llama population would correspond to a decline in the mite population.
After counting the number of mites in each layer of the core, Chepstow-Lusty found that their population skyrocketed when the Incan Empire dominated the Andes from 1438 C.E. to 1533 C.E.—the “golden age” of the Incan Empire. Francisco Pizzaro’s conquest of the empire, however, initiated a massive die-off of Indigenous people and their animals alike, and, as a result, the number of mites took a nosedive. The mite population rose again once Old World animals such as cows, pigs, and horses were brought to the area, but ultimately began to decline again around 1720, when a smallpox epidemic decimated the region.
Surprisingly, the researchers’ investigation of a second poop-eating microorganism, a genus of fungus called Sporormiella, contradicted the results offered by both the mite analysis and the historical record. Since Sporormiella live on herbivores and often reveal insights on the extinctions of large plant-eater populations, scientists often use Sporormiella spore counts to estimate the historical populations of big herbivores. However, the new study demonstrates that other factors can affect fungus populations in different environments, so relying solely on Sporormiella counts can give a misleading picture of population sizes. In the context of Marcacocha, Sporormiella counts responded to fluctuations in the lake’s water level, but didn’t correlate well with the chronology of the Inca Empire. “The spores may be saying more about the environmental conditions of the lake at that time,” according to Chepstow-Lusty, “rather than about the herbivores that may have been living around it.” Ultimately, moving forward, the researchers plan to conduct similar mite studies in Peru and other global locales to see if the technique holds its reliability. If proven reliable, the technique could be a powerful tool for uncovering the fate of other lost civilizations.