Zanoits are a type of microscopic organism. Each year, they kill off hundreds of thousands of Plantoids, which produce mellotoxins that would otherwise kill the Zanoits.
They are mentioned in "Ricardio the Heart Guy," when Ricardio discusses them with Princess Bubblegum to demonstrate his scientific knowledge. Ricardio poisons Finn and Jake with them in "Lady & Peebles."
One noticeable effect they can have on other organisms is rendering them unconscious, as Finn and Jake are completely incapacitated by the Zanoits until they are saved by Princess Bubblegum. In "Lemonhope Part 2," Phlannel Boxingday mentions he had to dispose of a synthetic Zanoit sterilizer bed compressor tube enlarger.
- Their name is misspelled as "Zanoids" in the game Sound Castle.