The mud demons live on the scorched planet and lie dormant within the ground or lakes until the planet's monsoon season begins. They are similar in some respects to scorpions, some reptiles and amphibians. When it rains, they emerge from the ground ready to kill, since they need to have their skin wet at all times. The mud demons have developed breathing holes in their tails to remain submerged even longer. They come in a variety of sizes, bearing razor sharp teeth, two legs, and a three-pronged scorpion-like tail, used primarily for grabbing and impaling. Their bite is paralyzing and venomous, depending on their size. The juveniles are more dangerous than the adults because they can't control the amount of venom injected into their prey. In addition to attacking directly, the mud demons also trick their prey during the dry season by raising their tails out of the water to hypnotize prey into believing the tail is the creature and attack. They tend to be extremely aggressive towards anything alive and edible. They are also not above cannibalism, shown when a mud demon ate its own innards despite being disemboweled by Riddick moments earlier.