Cockroaches

Cockroaches are common, non-magical insects found in both the Muggle and Wizarding world. While often regarded as mere pests, they appear in the series in several notable contexts: as a password to Albus Dumbledore's office, as a symbol of squalor and endurance, and as subjects for magical practice.

Cockroaches are mentioned on several occasions, often to emphasize unpleasant environments or as part of the broader magical backdrop.

• Password: In Harry Potter and the Goblet of Fire, Cockroach Cluster is the password required to access the office of Albus Dumbledore. Harry Potter uses this password to speak with the headmaster after his name unexpectedly emerges from the Goblet of Fire.
• Symbol of Squalor:
  1. When recounting his escape from Azkaban, Sirius Black tells Harry Potter that Peter Pettigrew would have been quite at home in the prison, remarking, “He'd have been welcome to my seat… I'd have been glad of the company… They've got a nice little Auschwitz going on there — plenty of company for him, as well… rats… and cockroaches…”. This highlights both the grim conditions of the wizarding prison and Pettigrew's affinity for vermin as a rat Animagus.
  2. The ancestral home of the Black family, 12 Grimmauld Place, is initially infested with numerous pests. After Harry Potter inherits the house and instructs the house-elf Kreacher to clean it, the text notes that the “ghostly sounds of scuttling” in the walls had ceased, implying that cockroaches were among the vermin purged from the home.
• Subjects for Magical Practice: While disguised as Mad-Eye Moody, Bartemius Crouch Jr. criticizes the practical lessons of previous Defence Against the Dark Arts teachers. He states that he would have had students “practising curses on rats and cockroaches” rather than facing creatures like Hinkypunks and Red Caps, indicating that cockroaches are considered common and ethically acceptable targets for students to practice spells on.

• Transfiguration and Curses: As noted by Bartemius Crouch Jr., cockroaches are considered suitable, disposable subjects for students to practice various forms of magic on, including curses. Their small size and abundance make them ideal for classroom exercises.
• Potions: While no specific potion in the seven novels is confirmed to use cockroaches as an ingredient, their commonality and resilience make them a plausible component for various concoctions within the field of Potions.

• In the film adaptation of Harry Potter and the Goblet of Fire, Harry Potter correctly uses the password “Cockroach Cluster” to access Dumbledore's office, and the gargoyle guarding it crumbles to reveal the spiral staircase. (film)
• In the video game adaptation of Harry Potter and the Chamber of Secrets, dried cockroaches are listed as a necessary ingredient for brewing the Polyjuice Potion. (video game)