Bloodsucker (STALKER)

Bloodsuckers from the game

S.T.A.L.K.E.R.

SHADOW OF CHERNOBYL

Bloodsuckers are a type of rare mutant usually found in the deeper areas of the Zone, often underground. They seem vaguely humanoid, with a hunched stance and height similar to that of an average person. Their eyes are lambent and their mouths are surrounded by several powerful tentacles used for feeding. 

The Bloodsucker is a semi-legendary creature, often used by Stalkers as a symbol of both the dangers and corruption of the Zone. This status has been achieved both thanks to the species’ relative rarity, as well as the fact that few humans who encounter Bloodsuckers survive to tell of it. 

Bloodsuckers often make lairs in which they will dwell while resting or storing their kill for later consumption. They also sleep standing up but aren't known to do so heavily, as even something as quiet as a light footstep will instantly awaken them.

In a fight,Bloodsuckers will primarily rely on their claws. They are very strong and few types of armor can withstand more than a few slashes. It is not unusual to find lone Bloodsuckers butchering entire squads of stalkers. While this can be seen as showing the Bloodsucker's fearsome skills, it is more likely a signal of the suicidal tendencies of the human AI, who seem to clump together and fire short burst while being slashed to death. In later AI improvements, however, it is not unlikely to see a group of humans kill a Bloodsucker, by surrounding it and shredding it with automatic fire.

Perhaps the most peculiar thing about Bloodsuckers is their optic camouflage, which allows them to temporarily become almost invisible to the naked eye. Bloodsuckers will often engage their camouflage upon discovering prey, and then become visible again when they are close enough to attack. Bloodsuckers have thick skin and are very durable, being able to sustain large amounts of damage before dying. After killing an enemy, Bloodsuckers will usually bite into the corpse to drain it of blood, which is what gave them their name.  

Mutation

Curiously, each species has evidence of severe decomposing – bits of flesh appear to be rotting off the body. All specimens seem to lack skulls as the skin on their heads peels away in areas to expose the brain underneath, perhaps explaining their lack of any sign of sentient intelligence or reason. This isn't present in most of the Bloodsuckers in the Clear Sky, and only in a handful in Shadow of Chernobyl before becoming a global trait in Call of Pripyat, perhaps suggesting that the Bloodsuckers in the area are evolving, or that the species as a whole is afflicted with a genetic disorder. However, it may also be a sign of aging.

How they continue to reproduce – and how there are so many only a few years after the first Emissions – is one of the larger mysteries of the Zone. (source)