Leeches are small slug-like creatures that live in water. They feed on human blood and/or that of other small invertebrates. Leech spit contains an anticoagulant (a substance that prevents blood clotting), allowing them to feed for longer than blood would normally flow.
The Hirudo medicinalis species (vulgarly known as the medicinal leech) are used in potion-making: to make the Polyjuice Potion, four unsucculated leeches are required.  Also, a dash of leech juice is a required ingredient in the making of the Shrinking Solution.  Flabberghasted leeches are also used in potion-making.
Behind the scenes
- The use of leeches in the Polyjuice Potion was chosen by J. K. Rowling to represent "[sucking] the essence out of one and into the other". Interestingly, the film prop used for Moste Potente Potions suggests that the leeches used have their suckers removed.
- Zygmunt Budge uses the phrase "hearts' content" (rather than "heart's content") in regards to leeches in Wonderbook: Book of Potions, properly using plural possession as leeches have two hearts.
- Harry Potter and the Chamber of Secrets (First appearance)
- Harry Potter and the Chamber of Secrets (film)
- Harry Potter and the Chamber of Secrets (video game)
- Harry Potter and the Prisoner of Azkaban
- Harry Potter and the Prisoner of Azkaban (video game) (GBA version only)
- The Road to Hogwarts Sweepstakes
- Wonderbook: Book of Potions
Notes and references
- ↑ Leech at Wikipedia
- ↑ Wonderbook: Book of Potions
- ↑ Harry Potter and the Chamber of Secrets, Chapter 10 (The Rogue Bludger)
- ↑ Harry Potter and the Chamber of Secrets (film)
- ↑ Harry Potter and the Prisoner of Azkaban, Chapter 7 (The Boggart in the Wardrobe)
- ↑ Pottermore - The Polyjuice Potion - J.K. Rowling's Thoughts