From the Super Mario Wiki
In Super Mario World 2: Yoshi's Island, the Official Guide from Nintendo Power describes how the Yoshi series has different enemy classes. Of those, one of them is Projectilia Ritebakatchia. Enemies in the class Projectilia Ritebakatchia throw projectiles at a Yoshi. They can usually be defeated by normal means, but sometimes they cannot be eaten. Common examples of these enemies include Wild Ptooie Piranhas, Blow Hards, Grinders with Super Green Watermelons, and Lakitus.