How did the monsters Scylla and Charybdis wreak havoc?

Scylla, a female six-headed monster, captured sailors and ate them. Charybdis was a whirlpool (or a creator of whirlpools) that swallowed ships.

The two creatures lay in wait on either side of the Straits of Messina between Italy and Sicily.

Their story is told in Homer’s Odyssey (ninth century B.C.).