The Grendel Jungle is the most inhospitable of the four eco-systems on the spaceship as far as your Creatures are concerned. There are biting insects, bacteria, and of course, Grendels. There are no leaf-producing plants or bug species, except for dragonfly nymphs. Dragonfly nymphs need leaves, both as food and to leave the Piranha Pool. However, a Creature with a sturdy immune system could live happily in the Jungle indefinitely -- there is plenty to eat, and Grendels can happily be incarcerated their whole life in there. One big difference between the Jungle and the Norn Terrarium is that the Norns, Ettins and Grendels take a far more active role in the ecosystem, mostly as prey species.