A Guard Worm is a large, violent worm, that guards various places in Bikini Bottom. They are a parody of guard dogs.
There is one in the episode "The Lost Mattress," named "JK," where it was living in the dump, at the moment when Mr. Krabs' misplaced a money filled mattress, Squidward was violently mauled by it various times.
There are various worms that work for the Bikini Bottom Police Force. In the episode "Slide Whistle Stooges," three guard worms were supporting the police to go against Squidward, but then attacked a police officer when he insulted them after they were going wild by the terrible whistle sounds Squidward made. They are light green and have silver spiked collars.