Eurystheus ordered Hercules to get rid of an enormous flock of birds which gathered at a lake near the town of Stymphalos terrorising and killing anyone who came near. These birds were maneaters, huge and fierce with vicious long, sharp, pointed beaks, massive lethal claws, and feathers of steel which they fired like darts. This gave them something like a coat of armour which made them difficult to kill.

Hercules had no idea how to drive the birds away. Then Athena gave him a pair of bronze krotala made by Hephaestos, the god of the forge. These were similar to castanets and when clicked together they made an awful row.

Hercules climbed a nearby mountain and clicked the krotala loudly, scaring the birds and causing them to rise into the sky. He then aimed a slingshot at their most vulnerable soft spots managing to kill them as they took flight.