The krell's appearance is unknown. Their natural predators include nightmaws, which hunted them on land, and deepwalkers that attack them when they are near the shore. The creatures are likely herbivorous, feeding on oceanside weeds.
The krell live together in herds and travel across the island on trails that they wear through the jungle. They often sleep beneath the roosts of Aviar. Due to this behavior, their minds are hidden from their predators by the Aviar's mental protection. However, some of their predators have learned that if they startle the Aviar away from their nests, they can again sense the krell minds.