Burpers

Burpers are a colonial organism that spawn from a tissue bed at the bottom of a pool or other body of water. Individuals bud off from the tissue bed, grow and develop underwater, and gradually form into spheres around a core of lighter than air gas. As they fill, they float to the surface and up into the air.

While airborne, burpers metabolize fog to synthesize more light gas and float until they find a new unoccupied pool. When they do, they vent their (highly toxic) ballast, making a distinctive burping sound. If they survive to sink to the bottom of the pool, they will attempt to form a new spawning bed, completing their life cycle. Burper ballast is caustic, and will cause sever burns to any exposed tissue. In a pinch, burpers can use this as a form of self defense. It is also highly flammable - shooting one with a blaster is not advised.

(concept submitted by oiseauxmorts)