Achemon and his brother Basalas were two Cercopes for ever quarrelling. One day they saw Hercules asleep under a tree and insulted him, but Hercules tied them by their feet to his club and walked off with them, heads downwards, like a brace of hares. Everyone laughed at the sight, and it became a proverbial cry among the Greeks, when two men were seen quarelling—“Look out for Melampygos!” (i.e. Hercules).
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894