Catachan was colonised by humans during the Dark Age of Technology, long before the Imperium of Man was established. When the first exploratory probes arrived in its star system, the planet was a deceptive, calm green orb when scrutinized from orbit, but when the first colony ships crash-landed on the jungle planet and the colonists had no way to escape, they discovered themselves to have arrived on one of the harshest and most dangerous planetary ecosystems in the galaxy. The colonists only barely survived, holed up in their spacecraft against a living, besieging jungle, a battle for survival in which undoubtedly many of them died before they finally managed to learn enough about their new homeworld to survive, if not thrive, beneath its jungle canopies. In time, their skill at surviving on Catachan came to the notice of the Departmento Munitorum, which realised that the Catachans would make excellent additions to the Imperial Guard as soldiers dedicated to service in some of the galaxy's most hostile planetary environments. This event was the day the first Catachan Jungle Fighters regiment was created.
- The Brainleaf, a vegetative carnivore, is a small tree, not particularly conspicuous on Catachan, but is able to attach its tendrils to the spine and brain of any animal, taking control over their body. This creature may actually be a genetic offshoot of the Tyranid Cortex Leech, a creature with similar abilities, that was cut off from the Hive Mind and went feral.
- The Spiker, another deadly plant, fires its spikes into its victims' bodies, which contain the Spiker's DNA and unleash a series of mutative chemical reactions which literally transforms the person into another Spiker.
- The Venus Mantrap is a carnivorous plant whose analogous species are common to many jungle Deathworlds across the galaxy. It resembles an oversized Venus Flytrap, but unlike the flytrap, it is not stationary but is able to move its leaves to attack and consume its prey. The Mantrap consists of a number of mobile leaves attached to a single immobile stem.
- The Catachan Devil, a voracious insectoid predator, is one of the most famous deadly animals of Catachan and looks somewhat like a many-limbed scorpion or centipede. They can be as long as a train but are very bulky and slow-moving, which means that escape is possible for the unlucky humans who confront one.
- Grox, although originally native to the Soloman System, are also found on Catachan, perhaps brought by the early human colonists. The animals are prized for their highly nutritious and tasty meat, and have been introduced to many worlds throughout the Warhammer galaxy, so that the Grox is now the most well-known livestock animal in the Imperium. The Grox however are extremely ornery and virtually impossible to keep under control without some form of brain-implants or lobotomy - on Catachan they have become wild, and are deadly predators.
- The Shambling Mamorphs of the volcano lands are tough fighters and put up a good fight even against the Catachan Devil.
- There are many types of serpents on Catachan, including the Flying Swamp Mamba, the Coiling Death Cobra and the Catachan Black Viper, all of which are deadly to most living beings. Some have toxin that is so powerful it can kill a man in under 30 heartbeats.
- Great Barking Toads, although appearing benign and harmless, are literally volatile creatures: the creature is easily startled, and anything it finds threatening is liable to cause it to explode in a cloud of toxins which kills anything within a one-kilometer area, including the Barking Toad itself. It's toxin is virulent enough that even respirators and sealed suits such as power armour offer no protection, hence why they are widely recognized as the most toxic creatures in the galaxy.