Some Headcanons on Pandora's fauna
Just pretend that I've ripped these headcanons straight from Sir Hammerlock's almanach. Read it in his voice if you want.
Skags
A skag's armor is made of hardened bone structure, and, much like the tusks of earth's babirusa, never stop growing, even to the detriment of the creature itself. When a skag reaches a certain age where their heavy armor hinders movement and frequently causes them to overheat, they are left behind by their pack - or, when food is scarce, cannibalised.
As extreme omnivores, they have evolved an immunity to just about every bacillus and poison Pandora has to offer. In fact, their gut flora is so noxious, improperly prepared skag meat may kill just as many people as the creature did when it was still alive and kicking.
While their digestive system may seem terribly inefficent (regurgitation of indigestible matter pushes out recently eaten, undigested food as well), skags have evolved to make this deficit an efficient hunting strategy: By, and there is no delicate way to put it, projectile vomiting/defecating onto prey and stalking it at a distance until they succumb to infection, they are able to take on much larger prey such as bullymongs.
Bullymongs
Their thick, dense coat does not only protect them from the elements, but is an adaptation the bullymongs went under in order to defend against the previously discussed skag hunting strategy. Their fur is water repellant and can protect their skin from the noxious fluids expelled by skag stomachs.
Their main diet contains very little meat, and they never hunt for food, preferring to scavenge meat instead - this doesn't make them any less deadly though, as bullymongs are notoriously territorial and aggressive.
Instead, they mainly use their strong forearms to dig up roots, grubs, eggs and newborn threshers. Even in their inhospitable habitats, their burrows extend deep enough to find what little plant matter is hiding under ice or ash.
Rakk
Before human colonisation of Pandora, Rakk were largely unagressive. It is believed that they attached themselves to then common megafauna to feed, though whether this was a symbiotic relationship seen in cleaner fish or rather a parasitic one is not known. Given that it's Pandora we're talking about, it's generally assumed to be the latter.
With humans largely exterminating Pandora's megafauna for fun and profit, rakk have recently become more aggressive, swooping down from the skies to attack any prey they can reasonably take down in large numbers.
The animal known as a rakk hive does in fact have another name, a rather vulgar one at that given its facial structure. However, it is rare to still see one alive that has not been infested by a colony of rakk who use its large body to protect and warm their young.
Threshers
Threshers can only thrive near water, as soft, wet ground aids their burrowing and they can only reproduce in large bodies of water.
The Hyperion corporation soon produced warning signs cautioning folks approaching thresher infested waters. However, local bandits immediately took notes and began what was called the great switcheroo - stealing the signs and denoting clean lakes as dangerous and vice versa, giving them exclusive access to potable water and entertainment as they watched unsuspecting bots and workers get devoured. Hyperion soon found out about this tomfoolery and attempted to correct the signage, causing even more confusion. Thusly, the signs lost their function, and when seeing a lake noted as "infested with threshers" one has about a 50/50 chance of becoming a thersher's dinner.
A Thresher's eyesight is actually very poor, it relies instead on its sensitive tentacles feeling differences in vibration and air temperature. The many sensitive "eyes" on their head and tentacles are in fact ganglia, giving them more individual control over their limbs. Funnily enough, this can lead to wires getting crossed and tentacles fighting each other for food.
Stalkers
Despite their fearsome reputation, stalkers are physically quite weak. In order to accomodate their ability to fly short distances, their bones are hollow and easy to break. In addition, their eyes which are placed underneath their split jaws are easily damaged even on accident and, due to their location, the animal in question can't see what's in front of its face as soon as it opens its mouth. Nice work there, mother nature.
In order to make up for these disadvantages, stalkers rely on ambush tactics, their high mobility and ranged spike attacks to overwhelm their prey. They are very prone to "hit and run" tactics. Succinctly put, they are invisible assholes.
Once a stalker has bitten down on a prey item, it is physically incapable of letting go until the prey is fully swallowed. More stalkers die from overestimating their deepthroating prowess than predation by hunters every year.
Varkids
Varkids are, objectively and scientifically speaking, the worst.
