Lost army ants once marched in a circle for two days until they died of exhaustion

In 1921, naturalist William Beebe observed a column of army ants in Guyana that had lost the pheromone trail of the main colony and begun following one another in an unbroken circle 370 metres around, each ant blindly trusting the ant ahead. It took two and a half hours to complete one lap, and the 'mill' persisted for two days until most of the ants died of exhaustion.

— William Beebe, Edge of the Jungle — Henry Holt and Company, 1921
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