Okay. I might as well elaborate a little on potential categories of 'hostile wildlife'. It is
very unlikely that I'll get more than a couple of these modelled and animated any time in the near future, but the main idea here is to brainstorm.
Meet the Locals: Mutants, Ghouls, Primitives and the Enraged
Examples: Reavers from Firefly, the infected from 28 Days Later/I am Legend, the Cult of the Bomb from Beneath the Planet of the Apes, martian colonists from Total Recall, the Fallout series, etc.
Countless worlds have been inadvertantly settled by survivors from crash landings, others, cut off from supplies for centuries or ravaged by nuclear fire and biological weapons during the Machine Wars, and a few feature tribes of monolith-worshipping primitives present for no clear reason. Many of their inhabitants have reverted to a more natural, quasi-nomadic existence, making camp in the shadow of ancient ruins and subsisting off a harsh landscape.
Genetic deformities and rabid, contagious aggression frequently blight such communities, but while all pose a potential threat, some can be reasoned with or even afford partners for trade or recruitment. Their high incidence of favourable mutations- including Gifted- and resistance to hardship can make them valuable allies.
Habitat: Anywhere (on marginal, ruined or monolith worlds)
Likelihood of hosility: Average to High
Behaviour: Nomadic, Territorial, Raider- varies
Best handled by: Physicians, Ecologists, Shapers
Ancient Artilects: Abandoned Oracles, Drones, Tripods, Monoliths, etc.
Examples: Box from Logan's Run, AIVAS from Anne McAffrey's Chronicles of Pern, Hayao Miyazaki's Laputa: Castle in the Sky, 2001 et sequels, yet more Fallout series...
In another holdover from the era of the Machine Wars, ancient military bunkers and vault installations occasionally house decaying machine intelligences, ritually re-enacting the orders of their long-vanished masters. Some are highly advanced, but most are scarcely more than automatons, and a rare few represent the legacy of truly ancient starfaring civilisations, enigmatically abandoned aeons ago.
Often discovered during mining excavations, such beings are dangerous even in their decrepit state, but others are simply confused, erratic or malfunctioning. A number are sympathetic to human interests, possible to repair, bypass, or reprogram, and guard a wealth of knowledge or hoard of precious artifacts.
Habitat: Ancient vaults, ruins
Likelihood of hostility: High
Behaviour: Territorial or Pacific
Best handled by: Artificers, Initiates
Drivodils
Examples: David Wyndhams's Triffids, Little Barber Shop of Horrors, the Mycons from Star Control 2.
A dangerous species of animate, intelligent plant life, Drivodils have spread to many worlds through their microscopic seed capsules, which can slip past quarantine unnoticed in crates and soil samples. Sadly, they quickly displace indigenous plant species and, armed with barbed stings and caustic pollen, also endanger local fauna, so that their extermination has been a foremost priortity for many planetary governors.
Ironically, Drivodils have recently proven to be an excellent source of Spice, making the expense of hunting them far more palatable, and experience Changeling inflitrators have proven that peaceful coexistence is not quite outside the realm of possibility.
Habitat: Jungle, wetlands
Likelihood of hostility: Very High to Total
Behaviour: Territorial, Defensive
Best handled by: Ecologists, Shapers, Changelings
Araks: Warriors, Lancers, Nurselings, Brood Sacs, Imperatrices and Overlords
Examples: Army ants, certain termite species, Tyranids/Zerg/Bugs/Aliens, the Mind Worms from Sid Meier's Alpha Centauri. (Loose goblin-equivalents, crossed with rust-spitters.)
Believed to form part of the Krech's genetic template, the insectile Araks share the same propensity for rapid reproduction and complex social hierarchy- unfortunately, unlike the Krech, they are unremittingly hostile, apparently unreasoning, and highly carnivorous. Swarming in large numbers across the landscape, their combination of acid sprays, razor-sharp appendages and psychic terror can make short work of even staunch veterans.
The Araks can be captured and converted to serve Krech masters, and contact by the Collective's psychic group-consciousness can also establish good relations with the creatures. How they have spread from world to world is something of a mystery, but it is theorised that some have evolved their psionic powers to the point of mind control, allowing them to commandeer human vessels for their own use.
Habitat: Plains, grassland, deserts
Likelihood of hostility: Total
Behaviour: Nomadic, Raider
Best handled by: Shapers (maybe), Collective, Krech
Quicksilver: Thread, Ganglia, Mercurials, Oozes
Examples/inspiration: The T1000 from Terminator 2, Thread from the Chronicles of Pern, Michael Crichton's Prey/the general Gray Goo scenario. Loose troll-equivalents (they feed off economic activity.)
Normally found deep underground or in caustic, volcanic environments where geothermal or chemical power sources are abundant, Quicksilver are believed to be remote descendants of artificial, self-replicating machine life-forms. Having evolved over millennia into a self-contained ecology, they occasionally feed off the energy grid of human settlements in order to proliferate and grow.
Quicksilver make troublesome pests, as they absorb most forms of energy and quickly regenerate damage, but most have scant interest in organic life per se, and seldom threaten it unless attacked. Exceptionally learned observers- such as the Keepers of the Secret Fire- may be able to train, bribe, or reprogram the creatures to aid in defence, ore extraction or terraforming efforts.
Habitat: Caustic or volcanic environments, anywhere near powerful energy sources
Likelihood of hostility: Low
Behaviour: Defensive
Best handled by: Artificers (maybe), Ecologists (maybe), Keepers of the Secret Fire
Hrex: Hosts, Rhizomes and Symbionts
Examples: The Goa'uld from Stargate, countless body-horror sci-fi tropes, possibly Jadzia Dax from DS9, medicinal leeches. All-purpose zombification tool for turning critters into something the player can kill and not feel bad about!
Widely considered a vile and unnatural life-form, Hrex is a fungus-like organism that seizes control of a host body and compels it to seek out new victims to infest. The organism greatly increases strength and aggression but is eventually fatal to the host- even a slight scratch or bite typically being enough for transmission. The disease is curable if caught early, but many victims fail to find help in time.
Hrex has adapted to many forms of host, including humans and certain plant species, and a few of the least virulent strains permit their host's will and reason to remain intact, even transmitting memories from host to host when transplanted into new bodies- a remarkable faculty adapted by certain Shaper colonies for their own use.
Habitat: Squalid or polluted environments, wetlands, wherever potential hosts are found
Likelihood of hostility: Very High
Behaviour: Hunter, Atavistic
Best handled by: Physicians, Shapers
Giant Roaches and Roachmen
Examples: The Judas Breed from Mimic, the Fly (1986,) the Bug from Men in Black, yet more Fallout series
With their immense resistance to radiation and chemical poisoning, the humble cockroach has proliferated greatly on many ruined worlds, growing to astonishing size and filling new niches in the absence of competitor species. Many are found inhabiting the ruins of ancient settlements, but some have also adapted to nocturnal lifestyles in the open forest, and others have smuggled aboard cargo vessels to infest poorly-maintained vault complexes. Though shy and fearful creatures, Roaches spread disease and steal rations.
Far more dangerous are Roachmen, believed by some to be the legacy of a freak medical experiment gone horribly wrong. Roughly humanoid and often intelligent, they have been known to kidnap, kill and even disguise themselves as human citizens, making them adept as hunters and infilitrators. Their magpie-like fixation on shiny objects also leads them to purloin valuable cargo, of which they can accrue substantial hoards.
Habitat: Squalid settlements and vault complexes, ruined worlds, jungles
Likelihood of hostility: Low
Behaviour: Pacific, Defensive
Best handled by: Good maintenance of infrastructure.
Remoras (or Hullsuckers)
Examples: The Mynocks from Star Wars, the Star Trek episode Galaxy's Child, yet more of Adolf Schaller's floaters...
Originating on Parem IV, in their natural state Remoras are free-floating silicon-based life-forms which ride the gas giant's aerial megafauna during migrations to the upper atmosphere and feed on ambient electrical storm-currents. This habit has unfortunately led them to roost on the hulls of visiting spacecraft, allowing them journey from world to world in a state of suspended animation.
Though posing no direct threat to humans, Remoras may damage, drain or consume the components and fuel of ships, vehicles and life-support, grow to significant sizes, have the remarkable ability to generate natural shields, and defend themselves with thunderbolts. As such, Remoras are significant pests. Only a handful of erudite scholars have ever managed to domesticate a Remora, but Jovians display a natural affinity with the creatures, perhaps due to similar evolutionary origins.
Habitat: Aerial, within poorly-maintained vaults, shipyards or plazas
Likelihood of hostility: Average to Low
Behaviour: Nomadic, Defensive
Best handled by: Artificers (maybe), Ecologists (maybe), Keepers of the Secret Fire, Jovians
'Natural' Predators: Wingrays, Amoebas, Licovores, Hulk, Sand Wyrms
'Natural' Prey: Qud, Hareem, Carpets, Gigans, Gossamer
'Natural' Flora: Mycon Bloom, Terran Pine, Vapok Tree, Albedan Coral, Strain X497
Many robust species well-adapted to a particular climate are deliberately transplanted from world to world in order to aid in large-scale terraforming projects, and may precede formal human colonisation by decades or centuries. Most are harmless unless deliberately provoked, give full warning of an attack, and/or adhere to strict territorial boundaries, but may nonetheless pose a threat to the wayward traveller who ignores their scent borders.
Spice ingestion becomes concentrated in the upper echelons of the food chain, and can usually be harvested in abundance from top predators. Populations can sustain hunting indefinitely given adequate time and space to recover, but the temptation to overharvest is best combatted through strict edicts and a strong presence of Ecologists. Some can even be trained as mounts and couriers.
Habitat: Varies by species
Likelihood of hostility: High for predators, low for prey, none for fauna
Behaviour: Territorial, Defensive for prey, Ambush, Raider for predators, typically none for flora
Best handled by: Ecologists, Shapers, Changelings
EDIT: Added entries for Quicksilver, Remoras, Hrex, Roaches, and natural flora/fauna