The Caterpillar

From Jimmy Neutron Wiki

The Caterpillar was an enormous caterpillar, who only appeared in the film.

When Ms. Fowl got shrunk by Jimmy's shrink ray, the Caterpillar tried to eat her, even during the Mom-and-Dad-are-gone celebration.

At the end of the film, the Caterpillar becomes Ms. Fowl's pet. He was voiced by Frank Welker.