Dung-Eating Mites Reveal Inca History

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March 28, 2007 — Scientists have found a new tool to measure the rise and fall of some ancient civilizations —  by counting excrement-eating mites.

The new technique, detailed in the current issue of the Journal of Archaeological Science, has revealed for the first time the level of trade and economic activity during the Inca Empire, which stretched from the present-day Colombian border to the middle of Chile.

The Inca ruled the largest empire on Earth by the time their last emperor, Atahualpa, was garroted by Spanish conquistadors in 1533.

Then, within a century, a population estimated at 30 million was reduced by 90 percent, devastated by newly introduced diseases such as influenza and smallpox.

Because the voice of the Inca has never been heard — it has long been considered the only major Bronze Age civilization without a written language — and because of the destruction of their heritage by the Spanish, the details of their rapid expansion and sudden catastrophic collapse are still poorly understood.

Now scientists from universities in Britain, France and the United States have found unusual witnesses to recount the most important times of the Inca Empire — fossilized Oribatid mites preserved in sediments at a lake about 30 miles from the Inca capital of Cuzco.

Related to domestic dust mites often found in carpets or mattresses, Oribatid mites are tiny invertebrates — about one millimeter across — that live in moist grassland and pastures where they break down vegetable matter, including the droppings of grazing animals.

The researchers used this fossil evidence for tracking the changes of large herbivores in pasture areas on trading routes. Their logic was the more the mites, the more the llama dung was available on the pastures.

"We used these dung-eating mites as an indicator of the llama caravans and the volume of trade passing along this route. At times of peak usage llama trains, consisting of up to 1,000 animals each, would pass along the valley," principal author Alex Chepstow-Lusty of Montpellier University in France, told Discovery News.

Analysis of layers of mud cored from the lake of Marcacocha, which is located close to a major Inca trading route across the Andes, showed a marked increase in the abundance of mite fossils as the Inca Empire expanded from the Cuzco area in the early 1400s.

A later, but very sudden drop in the number of mites corresponded with the collapse of the native population after the arrival of the Spanish and their own domesticated animals.

"Historical accounts from this time document that two-thirds of the llama population died of a horrendous skin disease," Chepstow-Lusty said.

When the Spanish introduced their own livestock, the frequency of mite fossils increased once again, starting in the 1600s, as a result of renewed activity.

The researchers recorded another major mite decline in the early 1700s, when an epidemic ravaged the human population, killing up to 600 people a day in Cuzco.

"The results of this research are remarkable. We can see the sudden development of the Inca empire in the Cuzco region more clearly than we have ever been able to see before," said Brian Bauer, an anthropologist at the University of Illinois at Chicago who has written several books on the Inca.

According to Chepstow-Lusty, the new tool has wide potential to study the growth and decline of other ancient civilizations, such as the animal-based Viking colonies in Greenland.

"It may even help us unravel what happened at the end of the last Ice Age or before, when large herbivores such as mammoths went extinct. We could tell whether they died out due to climatic causes or humans hunting them," Chepstow-Lusty said.