The Harpies are mythological creatures that are half woman, half bird that appeared in Carl Barks' comic story The Golden Fleecing (where they were referred to as Larkies) and its DuckTales adaptation.
They guard the legendary Golden Fleece which Scrooge wants to get to make a new suit. They offer Launchpad a dinner just to fatten him up and feed him to the Sleepless Dragon. They grew furious when they saw Scrooge steal the Golden Fleece and tried to take it back from him. However the Sleepless Dragon was also freed from its prison and was hot in pursuit. Scrooge finally realizes that Launchpad's life was important then the fleece. After covering the dragon's eyes with the Golden Fleece, the creature falls asleep.
The Harpies then thank Scrooge now that the dragon finally sleeps. One of the harpies, whose name is Anastasia, then wishes to marry Launchpad.