The Harpies are mythological creatures that are half woman, half bird. They appeared in Carl Barks' comic story The Golden Fleecing (where they were referred to as Larkies) and its DuckTales adaptation.
The Harpies 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 more important than 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, Anastasia, then wishes to marry Launchpad.
They officially return in the season two episode "Storkules in Duckburg!" where they were sent to ambush Storkules from the kingdom of Maceduckia after Storkules played his lute reigned over a swarm of Harpies which only caused chaos in the kingdom and got him banished by Zeus. The Harpies make a physical appearance when they start an ambush in Funso's Funzone as Storkules tackles one. After Storkules captures one Harpy by grabbing a basketball hoop and placing it on the monstrous bird, the other Harpies retreat the building.
When Louie reads the Junior Woodchuck Guidebook about Harpies, a Harpy steals his guidebook as the nephews, along with Webby and Storkules plan to rid off the Harpies pestering the city of Duckburg, thanks to the invented plan Harp-B-Gone done by the nephews in capturing the Harpies to save Duckburg. All the Harpies in Duckburg are locked in a storage in Donald's boat where Storkules puts a "Do not open" sign on the door to keep the Harpies from escaping.
Later that night, Louie plans to release the Harpies as a plan to save the Harp-B-Gone industry in which Storkules warns Louie that if he releases the Harpies, they could cause more havoc in Duckburg. Louie and Storkules prepare to keep the door shut to prevent the Harpies from escaping in which the Harpies prepare to break the door as Donald scolds Louie for bringing in "pets" in the boat as he accidentally lets the Harpies escape and carry Donald's boat away due to Storcules stating that he treasures Donald's friendship the most (the Harpies steal the most treasured possessions of others). Storkules and Louie arrive on the ship to rescue Donald as Louie plans to get rid of all the Harp-B-Gone merchandise as all the Harpies get tied up by Storkules. The rehabilitated Harpies help Scrooge McDuck's lemonade industry grow, in which Roxanne Featherly asks Louie during the news to know if he could keep the Harpies from stealing lemonade. One Harpy crashes into the screen during the end of the episode as Louie tells the audience that they're still working on that problem.