By Christine McGourty
BBC science correspondent
Scientists believe they have found a new way to track the rise and fall of some ancient civilisations - by studying fossilised mites that thrive in the dung of their livestock.
A team from America, France and Britain have been studying mites from the soil in the Andes in Peru and say the tiny creatures can provide clues to changing patterns of trade and of disease epidemics through history.
The researchers made the discovery, announced in the Journal of Archaeological Science, while studying mud cores from a lake near the town of Cuzco, the heart of the former Inca Empire.
Dr Mick Frogley, of Sussex University, UK, said: "We were looking at the lake sediments for evidence of climate change, but we found so many of these mites it piqued our interest."
The tiny bugs - not much more than a millimetre across - are related to domestic dust mites often found in carpets or mattresses.
Some species live exclusively in moist grassland and pastures where they break down vegetable matter, including the droppings of grazing animals.
When the scientists started to record the numbers of mites, they obtained a plot with a very distinctive pattern.
"It couldn't have been better if we'd made it up," Dr Frogley told BBC News. "It was that good."
They found a huge increase in the number of fossil mites as the empire expanded from the Cuzco area in the early 1400s. A sudden drop in numbers corresponded with the collapse of the native population after the arrival of the Spanish conquistadors.
Historical accounts from the time also document that two-thirds of the llamas in the Cuzco area died of skin diseases.
Studying ancient civilisations can be difficult when they have left no detailed written records behind. But the researchers say they now have a new tool for examining the fortunes of native populations in the Andes.
The mite methodology could have more wide-ranging applications in the study of economic and social changes in other cultures through history.
"The Inca were a test-bed," said Dr Frogley. "Now, the findings have given us confidence to look further back into the past at civilisations that pre-date the Inca.
"A lot less is known about their economic and social structures and why these other cultures disappeared from the archaeological record. The technique could help find some answers."
He said it could also be used to study the Viking occupation of Greenland, which was also an animal-based economy.