Rotsuckers were aerial creatures that preyed on creatures sleeping in empty Caterbird cocoons.
Presumably, Rotsuckers also attacked sleeping creatures in other areas, as Caterbird cocoons were quite rare. The Rotsucker first filled the cocoon with corrosive bile (they were also known to spit this bile when angry or frustrated), then sealed the opening with a hardening agent present in glands of the skin. The fumes from the bile soon killed the Rotsucker's prey. The bile then caused the hapless creature to decompose into a thick, viscous liquid. After 5-7 days, the Rotsucker drilled a hole into the cocoon with its razor sharp mouthparts, and drank the liquid inside. Interestingly, Rotsuckers appeared to be intelligent on a more-than-instinctive level; they were shown to hold long soliloquies in their minds, although they were incapable of verbal speech.