Whirlwinds are very rare hostile mobs that were added in the v1.02 update to the Aether mod. Whirlwinds move about randomly, and can drop down or climb up. If a player gets too close to a Whirlwind, it will fling them into the air, like a zephyr would, potentially harming the player. Although Whirlwinds are considered hostile in this nature, they can still spawn on Peaceful mode. When they are killed they can drop a wide range of items and blocks (or random drops) like a continuum orb. They come in several colors, ranging from black to gray to white.
Note: Since Aether II Alpha, they have been removed, with no news on when (or if) they will be added again.