The Cacodemon is a member of the Narereperea family, which is the classification for creatures which have a semi-gaseous body and whose only mobility is through floating above the ground.
The Cacodemon's natural environment is low-light, swamp-like areas on the other side of The Portal. Cacodemons do occasionally venture out into more open areas for hunting or exploration for a new territory to occupy. Their one large eye is well adapted to their low light environment, having several times the light amplification characteristics as humans eyes.
Cacodemons are carniverous, and despite their large mouths, they typically only hunt creatures about 1/3 their size. Humans, while not their natural prey, at least initially appear to the Cacodemon to be potential prey. It is interesting to note that even though they repeatedly stalk and attempt to kill all non "zombiefied" humans they encounter, they do not actually consume the corpses; they seem to take a bite of each one and leave the partially-consumed bodies where they fell. Cacodemons aquire their prey by stalking it, using height differences in the environment to sneak up horizontally first, and then move vertically within striking range of the unsuspecting prey. They also have a need to periodically absorb the various gasses that rise from the waters of their environment.
Cacodemons do not fight over territory, they just seem to not like a crowded swamp and will disperse themselves peacefully, with some individuals voluntarily leaving and searching out a new swamp territory. They spend at least one part of their lives living alone, hunting for themselves and searching for or holding a territory of their own, and then they pair with another cacodemon for the rest of their lives. Strangely enough, scientists have been unable to identify any internal organ differences between the individuals in such a pair. Cacodemon reproduction has not yet been observed, and youth specimins of cacodemon have never been found. How they reproduce is a mystery.