BlackJack's guard worm is a guard worm in the episode "BlackJack."
BlackJack's guard worm is a big light green worm, who has light red eyes with black pupils, and sharp, light yellow teeth. He wears a spiky metal collar attached to a chain.
When SpongeBob walks up to BlackJack's house so he could save his parents and comes to the porch and approaches the door, the Guard Worm reaches out from a rusty boat in the backyard. He barks at SpongeBob, who is easily frightened and says "Nice wormy."