Nematodes are creatures that look like worms and eat anything they can find. They first appeared in the episode Home Sweet Pineapple (which they ate one coral and a driver's boat and drunk SpongeBob's house then left.) and made a second appearance in Best Day Ever (which they are consuming The Krusty Krab, only to be lured out by SpongeBob and they fall asleep after SpongeBob becomes tired from the song). They are not often seen but if they are, they'll eat something. They seem to be lead by one leading nematode which calls out things like "hungry" or "thirsty" and leads its followers to food and drink. They mostly eat wood and Pineapple juice.
In "Opposite Day", when the realtor talks to Squidward about moving, she says, referring to his house, "As long as it’s not infested with nematodes, or surrounded by troublesome neighbors or something like that."
SpongeBob SquarePants is the second Nicktoon to mention Nematodes; the first time was Doug ("Doug Bags a Neematoad"). During a camping trip, Roger Klotz tells Doug about the creature and encourages him to catch it, in a manner similar to a snipe hunt.
In Home Sweet Pineapple, the nematodes copy one nematode (Ex: Nematode says thirsty, then other nematodes says thirsty as well).