Harpies (meaning "snatcher") are winged spirits of sudden, sharp gusts of wind. They were known as the hounds of Zeus and were dispatched by the god to snatch away (harpazô) people and things from the earth. Sudden, mysterious disappearances were often attributed to the harpies. The harpies were once sent by Zeus to plague King Phineus of Thrake as punishment for revealing the secrets of the gods. Whenever a plate of food was set before him, the Harpies would swoop down and snatch it away, befouling any scraps left behind. When the Argonauts came to visit, the winged Boreades gave chase, and pursued the Harpies to the Strophades Islands, where the goddess Iris commanded them to turn back and leave the storm-spirits unharmed.
Consequently, they are best known for constantly stealing all food from the blind son of Neptune, Phineas, but were driven away by the Boreads Calais and Zethes. The literal meaning of the word seems to be "that which snatches."
At Camp Half-Blood, there are "cleaning harpies" named Aello, Celaeno, and Ocypete. These harpies that come to eat demigods that sneak out of their cabins at night. They always refer to themselves in the third person, for example they screech; "Campers out of bed! Dinner for hungry harpies!" Percy Jackson refers to the cleaning harpies as if they were "crossbred with the dodo birds," and similarly to Cyclops, they are immune to lava and fire, as they wash the dishes with lava which, according to him should kill 99.9% of all germs.
Ella is one of the many harpies who snatch food from Phineas' picnic table. She's faster and more nimble than her sisters. When befriending with Percy, Hazel Levesque and Frank Zhang, she shows her ability to memorize a massive amount of facts she reads in books. Percy decides that they have to free the harpies from their curse (to be only able to eat from Phineas' table) which they accomplish with a gamble to the death, including Percy and Phineas both drinking Gorgon Blood, not knowing which vial was from which side of the monster. Later on, Ella is taken to Camp Jupiter by Tyson. When Percy, Hazel and Frank are talking about their encounter with Ella, they decide that she is too important to leave behind when they go to Rome because she has memorized a part of the Sibylline Books.
A harpy was known as the mother of Zephyrus, the west wind, sisters of Iris and daughters of Thauma, and Electra.
Phineas, a son of Neptune, like Apollo, had a gift of prophecies. Zeus was angered by the information he was revealing that he blinded him and sealed him away on an island with a buffet of food that Phineas could never eat. The harpies would always snatch the food from him and take it away, leaving Phineas to starve.
However, in The Son of Neptune, when Phineas was revived by Gaea, the tables have turned and Phineas is now the one to eat the food and be able to keep the harpies from his table though they are bounded to eat and can't consume any other food.
- The American Harpy Eagle is a bird named after them.
- They seem to have strange names, as two harpies are called 'Nuggets' and 'Teriyaki' in The Lost Hero.