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The Aliens (also known as Kharaa) and the subspecies that make up its hostile presence on various human installations are the product of a previously unknown Bacteria-like growth that rapidly evolves and directly sets in motion the events that lead up to the hostile encounters with humans, and was accordingly termed by TSF scientists as Bacterium. The Bacterium is the basic building block of the Kharaa and is responsible for the evolution and aggressive behavior of the Kharaa lifeforms. The creatures and structures that the Kharaa have at their disposal were previously not associated with the Bacterium whatsoever but were separate species that were infested and incorporated into the Kharaa gene pool (including structures such as the Harvester). Once assimilated, these species would be regularly reproduced, albeit re-purposed to better suit their role in the Kharaa, such as carapace and the razor sharp blades that Skulks and Fades evolved.

The terminology for the aliens is still being developed. At the moment, we refer to the aliens, and their whole system of bacteria, lifeforms and growths, as the "Kharaa"; and the pre-hive-stage presence as the "bacterium". The first TSF encounter with the aliens occurred aboard the Mongol's Sanjii mining facility. The tattered voice comm logs they extracted from the command network had one word that stood out, used again and again – "Kharaa!" "Kharaa!" Later, it was understood that this means "Watch out!" in Mongolian. By then, it had stuck.

The Kharaa began appearing on ships and bases throughout the Ariadne Arm a decade ago, slaughtering everyone on board. In almost every case the ship then wandered off course, and either destroyed itself by slipping into some gravity well (usually a planet or sun) or was tracked down and destroyed by the owners of the craft. Life support on bases and ships usually fails soon after the Kharaa take over, so even without military response, they don't last very long. However it is still unknown how their appearances on numerous ships and installations can be prevented, and until more conclusive information can be gathered by scientists, humans may never know how or why the Bacterium is capable of setting forth such a destructive onslaught without any early indication or warning.

Initially, the Bacterium only reproduces, slowly forming a mat, visible to the naked eye. All of these bacteria are in contact with one another, sharing data on their environment, and triggering responses to stimuli (like energy sources, or danger). They form a network that links all Kharaa lifeforms and structures and is responsible for the phenomenon of Hive Sight. It isn't until the presence of larger lifeforms that the next stage of alien growth, the Hive, begins. The hive contains all the information and abilities necessary to set off a cascade of events that rapidly leads to full-scale conflict. Like all the other Kharaa structures, TSF scientists speculate that hives are actually creatures that have been evolved into this form over an incredibly long time, and have observed that Kharaa structures, in general, tend to resemble aquatic forms of life, contrary to the Kharaa lifeforms that clearly originated from mammals and other similar creatures.

The bacterium seems capable of tapping a wide variety of energy sources. Heat and water are diverse enough, but it also finds the rich sludge used for nano-construction highly desirable. Fortunately, the same safeguards that prevent marines from automatically accessing these stores thwart the Kharaa too. Unfortunately, the aliens seem quite prepared for this sort of obstacle, building Harvesters atop resource nodes, that draw the sludge up and digest it. These chambers appear to have once been a species, much like the hive. What these resource chambers could have been used for before the Kharaa encountered us is a perplexing mystery. But they convert the sludge into a usable form, just as our resource towers do. As a result, marines and Kharaa end up fighting for the same resources. Defending these resources is vital to the Kharaa, second only to protecting their hives.

To destroy the human presence, the bacterium employs lifeforms of its own. These are the creatures that slaughter the crew of the ship or base, and the same creatures that are waiting for the Frontiersmen when they arrive to take the ship or base back. Kharaa species have natural weaponry and cunning that make them a match for the best equipped and most highly trained forces the TSF can deploy. Hives continue to spawn lifeforms over the course of a conflict, replacing lost aliens. Destroying all hives is the only way to cease the everlasting onslaught.


The Kharaa life cycle begins with the Egg, which is commonly found in large clusters around a Hive. The basic form of the Kharaa, the Skulk, hatches from an egg by biting through the membrane. It has been observed that when the threat to Kharaa territory becomes formidable, the aliens respond by evolving into different and stronger lifeforms as the situation demands. These lifeforms are classified as the Gorge, Lerk, Fade, and Onos, each with their own unique abilities and roles to fulfill.

Kharaa lifeforms are capable of communication through Hive Sight, an instinctive visual mechanism that allows them to identify friend from foe. The Kharaa also possess enhanced senses, more notably Alien Vision which grant perfect visibility in darkness.

Kharaa Lifeforms
Lifeform Abilities Description
Slot Alternate Movement

Skulk idle.gif


Bite slot.gif

Leap slot.gif

Sneak slot.gif

Basic lifeform that climbs walls to disorient and ambush prey.
Parasite slot.gif

Xenocide slot.gif


Gorge idle.gif


Spit slot.gif

Heal spray slot.gif

Heal Spray
Belly slide slot.gif

Belly Slide
Support lifeform that acts as healer, builder, and demolisher.
Gorge build menu slot.gif

Build Menu
Bile bomb slot.gif

Bile Bomb
Babbler bait slot.gif

Babbler Bait

Lerk idle.gif


Bite slot.gif

Poison Bite
Spikes slot.gif

Roost slot.gif

Flying lifeform that excels at dealing damage over time.
Umbra slot.gif

Spores slot.gif


Fade idle.gif


Swipe slot.gif

Blink slot.gif

Elusive lifeform that specializes in assassination and escape.

Stab slot.gif


Onos idle.gif


Gore slot.gif

Stomp slot.gif

Icon charge.png

Gigantic lifeform that absorbs damage and demolishes structures.
Bone shield slot.gif

Bone Shield


Evolutions (or Traits) are purchased upgrades that passively enhance Kharaa lifeforms' defensive, deceptive, or reactive capabilities. The Hive can evolve into different types to unlock evolution structures: Crag Hive (Shell), Shade Hive (Veil), and Shift Hive (Spur). Traits are accessed in the Evolve Menu and will cost Personal Resources depending on different lifeforms. Only one of two traits from the same evolution structure can be evolved by players, but they may switch traits any time with enough Personal Resources.

If all evolution structures are destroyed, the pair of unlocked traits will lose all effects and become inaccessible to players. However, players that already evolved a trait will retain their purchase and regain the trait's effects when the associated evolution structure is rebuilt.

Prerequisite Trait Description Additional Information




Increases total Armor pool depending on lifeform.
  • Armor bonus increases with number of existing Shells (maximum 3 levels).


Increases passive Health/Armor regeneration.
  • Regen bonus increases with number of existing Shells per 3% (maximum 3 levels = 9%) for maximum 80 HP.
  • It heals every 2 seconds (80HP Max.)
  • It only activates when out of combat (taking damage) for 3 seconds

Icon vampirism.png

Leeches health from enemies when you hit them with your primary attack.
  • Each lifeform gains a different percentage of maximum amount of health / armor per level for each successful attack.
    • Skulk Bite: 6.67% / 13.34% / 20% of max health / armor
    • Gorge Spit: 2.67% / 5.34% / 8% of max health / armor
    • Lerk Bite: 2.67% / 5.34% / 8% of max health / armor
    • Fade:
      • Swipe: 3.33% / 6.66% / 10% of max health / armor
      • Stab: 6.66% / 13.33% / 20% of max health / armor
    • Onos Gore: 1.83% / 3.66% / 5.5% of max health / armor




Reveals nearby Marines and Exosuits' presence and indicates their health by colored icon.
  • Reveal range increases with number of existing Veils (maximum 3 levels).


Renders the lifeform almost invisible based on tier level, even while moving.
  • Each Veil increases the effect of the cloak when standing still and moving (Maximum 3 Levels).

Icon focus.png

Increases attack damage at the cost of attack speed.
  • Each level increases attack damage and decreases attack rate.
  • Only primary attacks are affected by Focus and consume 33% more energy.
  • Vampirism heals 33% more health if Focus is selected.



Icon adrenaline.png

Increases recharge rate of energy.
  • recharge rate bonuses increase with number of existing Spurs (maximum 3 levels).
  • recharge rate is tailored for each lifeform.

Icon celerity.png

Increases move speed.
  • Move speed bonus (0.5) increases with number of existing Spurs (maximum 3 levels = 1.5).

Icon crush.png

Increases damage inflicted on the armor of Marines and Marine structures.
  • Each level increases the fraction of damage dealt to Marine players' armor by 7%
  • Each level increases the damage dealt to Marine structures and Exos by 7%


Main article: Alien Commander.

The Alien Commander is a hive mind presence that governs over Kharaa territory and evolution. It aids in coordinating lifeforms, spreading the Kharaa Infestation, and growing various organic structures. Any lifeform can enter an unoccupied Hive to act as the Alien Commander, which changes the player's perspective from first-person to an overview of the map. Only one Commander can be active at a time, and he may exit the occupied Hive to become his previous lifeform.

The Commander has a user interface that includes a Mini-map, commander menu, and resource counter, allowing him to build structures and perform upgrades for the Kharaa. He can also assist his lifeforms using various abilities at his disposal; commander abilities cost Team Resources and are mostly found in the Assist tab, with some requiring the presence of specific units and structures to trigger.


See Alien Commander Abilities


Main article: Biomass.

Biomass is a tech progression system that serves two functions: increase all lifeforms' maximum Health pool and enable unlocked lifeform abilities after research from the Hive. Each Hive can contain up to 3 Biomass levels; 1 level for being an active Hive and 2 additional levels can be upgraded by the Alien Commander.

Biomass Levels & Unlocked Abilities with research costs and time
Level 1 Level 2 Level 3 Level 4 Level 5 Level 6 Level 7 Level 8 Level 9 Level 10
Biomass bar 10.jpg
Babbler Egg Rupture Bone Wall Leap Umbra Bone Shield Stab Stomp Xenocide Contamination
Babbler egg icon.gif Rupture icon.gif Bone wall icon.gif Leap icon.gif Umbra icon.gif Bone shield icon.gif Stab icon.gif Stomp icon.gif Xenocide icon.gif Contamination icon.gif
15 Alien res.png
40 seconds
20 Alien res.png
45 seconds
20 Alien res.png
20 seconds
25 Alien res.png
60 seconds
25 Alien res.png
60 seconds
25 Alien res.png
60 seconds
Web Charge Bile Bomb Umbra Advanced
Webs icon.gif Charge icon.gif Bile bomb icon.gif Spores icon.gif Adv Metabolize.png
15 Alien res.png
40 seconds
15 Alien res.png
40 seconds
20 Alien res.png
45 seconds
20 Alien res.png
45 seconds
Nutrient Mist Metabolize
Nutrient mist icon.gif Metabolize
20 Alien res.png
40 seconds
Gorge Egg Fade Egg
Gorge egg icon.gif Shadow step icon.gif
Lerk Egg Onos Egg
Lerk egg icon.gif Onos egg icon.gif
  • Maximum 12 Biomass levels (levels 11 and 12 do not unlock additional abilities, but grant increased HP to lifeforms and certain structures)
  • Unlocks specific lifeform abilities once researched from Hive.
  • Enables Alien Commander abilities and pre-evolved lifeform Eggs.
  • Increases maximum Health pool depending on lifeform.


Main article: Infestation.

Infestation is a green moss-like collective mass of billions of microscopic Bacterium. It grows outward from the Cyst, Hive, Tunnel, and Contamination structures, and is essential to Kharaa territory expansion. The Alien Commander can sprout any Kharaa structure directly from the Infestation itself.

Most Kharaa structures require Infestation to survive, except the source structures which produce the organic substance. Infestation is also sustained by the source structures, as otherwise, the Infestation will dissolve rapidly into nothing with its source destroyed. Infestation possesses corrosive properties that damage Frontiersmen structures' Armor, along with the sticky mass that slows down blueprint construction when in contact.


Main article: Maturation.

All Kharaa structures will automatically undergo a growth process known as Maturation. A newly grown structure is low on Health and Armor, but as the structure matures, it will reach its strongest state. The Alien Commander can use Nutrient Mist to rapidly mature structures even in their unbuilt state.

Units and Structures

Units and structures are placed by the Gorge and the Alien Commander specifically and the cost of structures placed by the Alien Commander is taken from the Team Resources.

WhipShiftShadeCragHiveHarvesterDrifterCystCrag HiveDrifterCystShift HiveDrifterShellVeilSpurCystShade HiveDrifterVampirismCarapaceRegenerationFocusCamoflageAuraCrushCelerityAdrenalineBiomass 1Biomass 2Biomass 3Biomass 4Biomass 5Biomass 6Biomass 7Biomass 8Biomass 9Biomass 10Bile MineWebRuptureOnos ChargeBone WallBile BombMetabolizeLeapSporesUmbraAdvanced MetabolizeBone ShieldStabStompXenocideContaminationAlien TechtreeTEST.png
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