Snails and Slugs in the Wizarding World

Snails and their close relatives, slugs, are common gastropods found in both the Muggle and Wizarding world. Within the magical community, they are most notably utilized as practice subjects in Transfiguration, as ingredients in Potions, and appear as common garden pests. Additionally, several magical snail-like creatures exist, some of which possess properties valuable to witches and wizards.

• In Transfiguration: Snails are used by students at Hogwarts to practice the Vanishing Spell (`Evanesco`). In their fifth year, students in Professor Minerva McGonagall's class are tasked with vanishing snails before moving on to more complex subjects like mice, in preparation for their O.W.L. examinations. Harry Potter is noted to have successfully vanished his snail on the first try.
• In Potions: While snails themselves are not explicitly named as an ingredient in the novels, their relatives are. Horned slugs, for instance, are a required ingredient for the first-year Boil Cure Potion. This indicates that gastropods are a standard component in elementary potioneering.
• As Pests: Much like in the Muggle world, slugs are considered a nuisance in wizarding gardens. Molly Weasley once complained about having to de-slug the cabbages in the Burrow's garden, in addition to de-gnoming it.

• Streeler: A giant magical snail that changes colour on an hourly basis. It is known for its highly destructive venomous trail, which scorches and kills all vegetation it passes over. The venom is one of the few known substances capable of killing Horklumps. A Streeler's shell, prized for its colour-changing properties, is used as a Potions ingredient. (Fantastic Beasts and Where to Find Them)
• Horklump: Though often mistaken for a mushroom, the Horklump is a creature. It resembles a fleshy, pinkish growth covered in sparse, wiry black bristles. They are a garden pest known for their rapid propagation. Gnomes are known to eat them. (Fantastic Beasts and Where to Find Them)

• Ron Weasley's Slug-Vomiting Charm: In his second year, Ron Weasley attempted to curse Draco Malfoy for calling Hermione Granger a “Mudblood”. Ron used the incantation `Eat slugs!`, but because his wand was broken and held together with Spellotape, the spell backfired. This resulted in Ron vomiting a continuous stream of large, slimy slugs, requiring a visit to Rubeus Hagrid's hut to wait for the effects to wear off.

• In the film adaptation of `Harry Potter and the Chamber of Secrets`, the slugs Ron vomits are depicted as very large, live gastropods. The scene is a memorable example of practical and special effects used to portray the unpleasant consequences of a backfiring spell. (film)