Zeb

From Wikitroid, the Metroid wiki

Mysteriously, Brinstar (and many other areas in Zebes) is covered in green pipes which look similar to the pipes in Super Mario Bros., another Nintendo game. The Zeb fly out of these pipes at the enemy. However, they are very lightly armored and do not do much damage. They continue to attack in infinite numbers, so standing in front of a pipe and repeatedly killing them for their health or missile powerups is an easy way to recharge in the absence of an Energy Station or missile station. There is a unique pipe enemy for each region of Zebes.