Air Holes are artifical pipe-like structures protruding from floors and walls below Zebes' surface that strongly resemble Warp Pipes from Super Mario Bros. Indeed, in the 1986 manga, Samus mistakes it for one. They are only seen in the 2D Metroid games. Like Warp Pipes, they come in a range of colors and a few of them can be entered by Samus.
Some of these Air Holes, however, have small creatures emerging from them which immediately attempt to tackle Samus by flying toward her. Zebs, Geegas, Zebbos, and Gamets can be seen exiting from them, depending on the region of Zebes. Samus can repeatedly kill them for energy and ammunition because the creatures emerging from these pipes continually respawn; this leads to a theory that the spawned enemies have constructed hives within these tunnels. There are underwater crustaceans called Zoas that are considered Air Hole-spawned creatures like the ones mentioned above because of their limitless spawning and attack pattern, despite that Zoas only emerge from sandpits found in Maridia instead of Air Holes.
Other than sandpits, it is interesting to note that some other crevices found on the ground throughout Zebes, some of which are filled with either lava or acid, will also continuously release the Air Hole-spawned enemies.
On planet SR-388, there are several corridors containing vine-like tunnels on the floor that infinitely release Gawrons, Skreeks or Yumees, serving the exact same function as Zebes' Air Holes. In some areas of the planet, these creatures will emerge from pools of hazardous liquid. However, the enemies will cease to fly out from their respective nests whenever 10 of these are killed. This would suggest that the creatures become concerned in preserving their lives rather than continue sending more of their own to face the threat.
- One Air Hole in Brinstar of Super Metroid can be entered for a Missile Tank.
- The Plated Puffers, Puffer Mines, Phazon Puffers and Phazon Metroids encountered in Metroid Prime and Metroid Prime 3 can be somewhat considered pipe enemies as well, as they are infinitely spawned from openings in certain rooms the creatures can be found in.