What Llama-Poop-Eating Mites Tell Us About the Rise and Fall of the Inca Empire

The Inca Empire owes much to the humble llama—and to the animal’s droppings. As a 2011 study of the fallen Andean civilization revealed, llama dung served as an essential fertilizer for the Incas’ staple crop of maize, enabling the Peruvian-based group to embrace agriculture and move away from the less reliable method of hunting and gathering. Now, Lizzie Wade reports for Science magazine, scientists are once again drawing on llama excrement to unlock the secrets of the Inca—only this time, their focus is not simply the civilization's storied rise, but also its devastating downfall.

To track the rise and fall of the Inca civilization, the new research—recently published in the Journal of Archaeological Science—relies on oribatid mites, which are tiny spider relatives that once feasted on the feces of llamas passing through their home in the Andean Marcacocha lake. Led by paleoecologist Alex Chepstow-Lusty of the University of Sussex, the study’s authors describe a strong correlation between Marcacocha’s mite population, as represented by specimens preserved in sediment cores retrieved from the now-muddy wetland, and that of the llamas (and, in a roundabout way, humans) the critters relied on for sustenance.

According to Wade, the team found that the mites’ numbers skyrocketed between 1483 and 1533, or the period when the Inca dominated the Andes region. During this golden age, Marcacocha was a popular thoroughfare for Inca merchants, who may have passed through the lake and its surrounding grasslands on their way to and from the ancient city of Ollantaytambo.

Accompanied by llamas tasked with carrying trading wares such as maize, salt and coca leaves, these travelers inadvertently boosted the lake’s oribatid mite population. As Chepstow-Lusty explains to the London Natural History Museum’s Josh Davis, their trading networks brought thousands of caravan-pulling llamas to a road, essentially “a highway over the mountains,” by the lake. After refueling with an invigorating gulp or two of water, the llamas defecated “en masse,” to borrow Wade’s words, and sprinkled the ground with feces that soon washed into the lake, where it was eagerly consumed by Marcacocha’s resident mites.

At the peak of the Inca’s power, more llamas wandered through the area, keeping its mite population well-fed. But upon the arrival of Spanish conquistadors led by Francisco Pizarro in the mid-16th century, the indigenous civilization quickly succumbed to violence and disease. By 1570, Mark Cartwright notes for Ancient History Encyclopedia, around 50 percent of the region’s pre-Hispanic population had been wiped out.

Anne Baker, a mite researcher at the Natural History Museum and co-author of the study, tells Davis that the lake-dwelling mites decreased in number alongside their human and llama counterparts. Although they somewhat recovered following the Spaniards’ introduction of Old World animals such as cows, horses and sheep, a 1719 smallpox epidemic again decimated both indigenous and animal populations, leaving the mites starved for food.

Interestingly, Wade writes for Science, the researchers’ investigation of a second poop-eating microorganism—Sporormiella, or fungus spores that live on herbivores and often reveal insights on the extinctions of large plant-eater populations—contradicted the results offered by both the mite analysis and the historical record. Usually, a drop in Sporormiella indicates species extinction.

But for the Marcacocha sample, it seems the spores fared best in dry periods, which found llamas pooping closer to the center of the shrinking lake. Conversely, the spores shrank during periods when the lake was brimming with water.

In the study, the authors explain that oribatid mite numbers tended to reflect the “well-documented, landscape-scale events” associated with the Spanish invasion, while Sporormiella spores remained “largely muted” throughout these same periods. It’s possible, they add, that Sporormiella studies offer misleading data when conducted on small, shallow lakes such as Marcacocha, and should therefore be considered in conjunction with alternative sources such as mite population figures.

“The spores may be saying more about the environmental conditions of the lake at that time,” Chepstow-Lusty tells Davis, “rather than about the herbivores that may have been living around it.”

Moving forward, the researchers hope to conduct similar mite studies at small lakes in Peru and other global locales. If the technique proves reliable, Chepstow-Lusty says, it could be used to uncover the fate of such lost civilizations as the sheep-dependent Vikings of mid-14th century Greenland. As he concludes, “Mites live in most regions of the world.”

Meilan Solly | | READ MORE

Meilan Solly is Smithsonian magazine's senior associate digital editor, history.