Mites that eat llama dung are providing scientists with critical new clues to the rise and fall of the Inca empire and the civilisations that preceded it.

The soil invertebrates are allowing researchers to trace the growth and decline of the peoples of the Andes several centuries before the Spanish conquest in 1532 brought written records to the region for the first time.

The evidence gleaned from fossilised mites, preserved in sediments at a lake about 50km (30 miles) from the Inca capital of Cuzco, has shown how the great empire increased in size and complexity in the early 15th century.

The abundance of the fossil mites is directly linked to the amount of llama dung that was deposited on the pastures around Lake Maracocha at particular times, and can thus be used as a proxy for estimating the size of the herds and pack trains that grazed there.

From this a team led by Alex Chepstow-Lusty, of Montpellier University in France, has been able to reconstruct the fluctuating fortunes of local populations for an era from which no written records exist.

The new research suggests that after a period of sharp growth, the Inca civilisation’s power had already started to wane immediately before the arrival of Francisco Pizarro’s conquistadors. This could reflect the advent of European diseases to which indigenous people and livestock had no resistance. Even further back in history, the mite records also show how two earlier civilisations, the Whari and the Tiwanaku, moved higher into the Andes as temperatures rose during the 11th century, then declined, partly because of prolonged drought.

Dr Chepstow-Lusty said that the mite evidence opened a valuable new window on a period that has always been difficult to study because Andean civilisations never developed forms of record-keeping.

“We don’t have any historical documents before the Spanish arrived, and we have had to rely on archaeology and evidence from things like pollen and charcoal,” Dr Chepstow-Lusty said. “What we have now is a new tool that can be used directly to study large herbivore populations, which in this part of the world are intimately linked to humans.”

In a paper published in the Journal of Archaeological Science, his team has shown how mite numbers rise and fall in concert with well-documented socio-economic changes in the postconquest period. “When the Spanish arrived, the Inca seem already to have been in some kind of decline,” Dr Chepstow-Lusty said.

How invertebrates followed the empire

c1100 AD Whari and Tiwanaku civilisations start to decline. First major dip in the mite record from Lake Maracocha seen

c1200 Inca civilisation starts growing in Cuzco region

c1400 First signs of Inca expansion in mite record

c1438 Dramatic expansion of Inca empire; dramatic increase in the number of mites found at Maracocha

1525 Death of Huayna Capac provokes civil war between his sons, Huascar and Atahualpa. Mite data suggests decline

1532 First encounter between Francisco Pizarro and Atahualpa at Cajamarca, at which 168 Spaniards defeat Inca army and kidnap Atahualpa

1533 Murder of Atahualpa by the Spanish, followed by a rapid depopulation of the region because of smallpox and other diseases

1544-45 Two thirds of llamas in Cuzco area die of llama mange, a skin disease imported by the Spanish. Further fall in mite numbers

1572 Defeat of Tupac Amaru, the last Inca leader to resist Spanish rule

c1600 Reestablishment of rural communities in the region. Mite numbers begin to rise again

1719 Plague strikes Ollantaytambo region, with one hacienda reporting the loss of almost all indigenous workers. Mite numbers fall again

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