The Worm-Mobile is a mobile invention of Aviva's, built for the Kratt brothers as a means of underground travel. Small and pink in color, it was modeled and designed after the worm. It has segments to divide it's body. It was introduced in the episode Mystery of the Squirmy Wormy.
The Worm-Mobile first appeared in "Mystery of the Squirmy Wormy"; Aviva had originally built it for Chris as a better means of transportation through the underground tunnels. When Martin and Pinky were taken by an American robin back to it's nest, the Worm-Mobile was damaged by another robin. Chris, with his ingenuity and quick thinking, fixed it, and went after his brother.