Melon Bug

Melon Bugs are bug-like NPCs that can roll into balls which look like melons in Super Mario World 2: Yoshi's Island and Yoshi's Island: Super Mario Advance 3.

They bounce up and down, but when Yoshi gets too close, they hide in their "melons". If Yoshi gets close enough, he can eat them and then spit them out so and they will roll in their "melons", destroying enemies that they touch.