Muncher

Munchers are a type of Piranha Plant found first in Super Mario Bros. 3. They are small and black. They appear in large groups taking up space between the space of two pipes. If stepped on Mario will get hurt or die. Using Yoshi in Super Mario World you can walk across them and not get hurt. In the Pipe Maze in SMB3 there is a level where there is a large line of Munchers and the only way to get across them is to use a Starman.