Project GeeKeR (1996)

Geeker gets a pet alien worm. Becky can't stand worms, and convinces GeeKeR to set the worm free in the tunnels under the city. But neither of them realizes that this type of worm grows to fit whatever it is kept in; down in the tunnels it becomes enormous. Moloch harnesses the giant worm and uses it to track down GeeKeR. Soon, both GeeKeR and Noah are captured, and the only way Becky can save them is to overcome her revulsion and team up with the worm.