A maggot is the larval form of some varieties of fly, including houseflies, cheese flies, and blowflies.
Luna Lovegood believed in pale, brain-like creatures called Aquavirius Maggots, but it is likely that these do not exist.
If an unworthy Dark wizard or witch attempts to cast the Patronus Charm, rather than summoning a spirit guardian, as the spell normally should, a horde of maggots will burst out of the caster's wand and start to consume him or her. The first recorded instance of this happening was with the Dark Wizard Raczidian.
Kreacher sent a package of maggots to Harry Potter for Christmas in 1996 as a means of showing his dislike for his new master.
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