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"Watch the headhumpers, Gordon."
Barney Calhoun[src]

The Poison Headcrab (or Toxic Headcrab in Half-Life: Alyx) is a venomous Headcrab variant, and one of the four known varieties of Headcrab. Like its relatives, the Poison Headcrab is able to convert humans into Zombies.


The poison headcrab is identifiable by its dark skin and elongated legs. It is the largest of the headcrab subspecies seen on Earth with a bulky body and thick long legs. It is equipped with four fangs on its front with the two outer fangs extending further down, similar to those of the common headcrab. Its four long legs extend out from its body and are covered in bristles like its body. Each leg has a single joint, which helps the creature navigate and raise its body up from the ground, and ends in a singular sharp claw which helps it latch on to its prey. The skin around the joint is red in color, with a white band running across the joint itself. These markings are possibly aposematic in order to warn off potential predators of its venomous nature.

in Half-Life: Alyx, poison headcrabs have a similar appearance but have a dark, grey coloring as opposed to the black coloration in Half-Life 2. The bright white and red markings are also darker.

Behavior and skills[]

The poison headcrab is the slowest of the headcrabs in terms of movement despite its long legs. They move at a sluggish pace by slowly positioning each leg in a deliberate fashion. The only time they move in haste is when they receive damage, at which point they will skitter for a short distance to safety. Due to its slow movement, the creature primarily relies on ambush, hiding behind objects or waiting on higher ground to catch unsuspecting prey. When cornered or noticing prey, it will give off a distinct rattling sound before attacking head on. Like all headcrabs, they attack by jumping on to their prey. However, poison headcrabs are comparatively slower in this regard as well, and cannot string together attacks as well as the other headcrab subspecies.

Poison headcrabs possess a potent neurotoxin that acts both as a poison and venom. The headcrab delivers this toxin to its victim's bloodstream via its fangs. A bite from the poison headcrab will not kill the victim but severely weaken it, allowing the poison headcrab to easily attach to them. While it is not lethal as a venom, this toxin is a lethal poison; ingestion of the compound will immediately result in death. Consequently, a predator that eats the poison headcrab will likely die from the effects of this toxin.

Poison Zombie[]

Main article: Poison Zombie

Like all headcrabs, poison headcrabs can latch onto a human's head and take control of their nervous system, turning the host into a zombie. Just as the poison headcrab is slower than its cousins, poison zombies move slower than other zombies. They appear bloated and hunched, the latter due to the host missing most of its supportive back muscles. Aside from its controlling Headcrab, Poison Zombies usually host two or three more Poison Headcrabs on its back. When faced with an enemy, these Headcrabs can detach or be thrown by the zombie towards the enemy. A Poison Zombie will typically try to exhaust all its Headcrabs before attacking itself with its mutated claws unless the target is too close.


A bite from a poison headcrab will invariably reduce the player's health to 1, after which the HEV Suit will administer an antidote that will slowly regenerate the player's health minus the headcrab's bite damage. This will leave the player vulnerable to other threats in the area so it is advised to get some distance from the Poison Headcrab and any other threat in the area when bitten. Preemptively, it's better to avoid the bite entirely which is relatively easy; poison headcrabs are slow to attack and will telegraph their movements so the player knows when it will jump. Avoid the attack by going sideways as moving backwards can still guarantee a hit from the headcrab. Poison headcrabs cannot attack consecutively as fast as the common or fast headcrabs, so the player has a good chance to kill it after it jumps.

Since poison headcrabs have higher health than most headcrabs and tend to run when shot, taking one out quickly requires a weapon that deals damage immediately instead of gradually. The SPAS-12 shotgun is a good weapon for this; one shot at close range will kill a poison headcrab instantly. Another good alternative is the .357 Magnum, which is a one-shot kill at any range, making it good for eliminating them before entering their range. Like all headcrabs, poison headcrabs can be stunned and killed with 3 blasts from the Gravity Gun, though this method is less effective than just picking up a heavy object then launching it at the headcrab, which kills it instantly. Poison headcrabs can also be killed with one hit from a crowbar. This can be risky due to getting close to the headcrab so hit it before it has a chance to jump or avoid the jump then hit it.

It's better to take out poison headcrabs first before focusing on other enemies due to their venomous bite. Poison headcrabs prefer to hide when they can as opposed to staying out in the open, which can make locating them difficult. Fortunately, they are vocal creatures and will make themselves known with their distinct vocalizations. When the player hears the sound, they can immediately know one is present and, provided there is no other threat, look for it and kill it.


Headcrab Poison beta

The Beta Poison Headcrab.

  • According to Half-Life 2: Raising The Bar, the development team noticed that, upon hearing the Poison Headcrab's sound, playtesters would frantically start looking around for the Poison Headcrab so they could destroy it, regardless of any other present dangers.[1]
  • Poison headcrabs will inflict bite damage as well as its venom damage, so the player will regenerate with 10 less health. However, if the player has less than 10 health, the bite will only reduce health to 1 and not inflict any extra damage. Therefore, poison headcrabs by themselves aren't actually able to kill the player.
  • Its model contains an unused animation called "Spitattack". This suggests the Poison Headcrab may have had a ranged attack at some point.
  • The Poison Headcrab's second scream, "ph_scream2.wav", appears to be a sped-up version of the Fast Zombie's first scream ("fz_scream1.wav", the "Howie Scream").[2]
  • Poison Headcrabs are extremely dangerous to NPCs, as they lack Gordon's HEV Suit and thus have no access to the antidote for the neurotoxin. As a result, a hit from a Poison Headcrab will permanently reduce an NPC's health to 1, causing them to be instantly killed the next time they receive damage. Essential NPCs like Alyx Vance and Barney Calhoun regenerate health, so the poison headcrab is less of a threat to them, provided they are not under attack by other enemies around the time of the bite. The Citizens, however, can be healed with Medkits to restore their health.
    • Grigori is the only NPC immune to this enemy.
    • Barnacles die instantly upon eating a poison headcrab.
  • In Half-Life 2, the Poison Headcrab has a minimum distance for an attack: if the player is touching it, then it will not attack but instead crawl away to reach the minimum distance (unless against a wall).
  • Though there are two Poison Headcrab NPCs, npc_headcrab_poison and npc_headcrab_black, they are linked to the same entity definition, as found in the Source SDK file npc_headcrab.cpp:
    • LINK_ENTITY_TO_CLASS( npc_headcrab_black, CBlackHeadcrab );
    • LINK_ENTITY_TO_CLASS( npc_headcrab_poison, CBlackHeadcrab );
      • The file npc_headcrab.cpp also indicates that the npc_headcrab_poison NPC has slightly more defined AI, probably because the npc_headcrab_black NPC rarely (if ever) appears anywhere but on a Poison Zombie's back, while the npc_headcrab_poison appears elsewhere (ex. on the ground).
    • The names "Black Headcrab" and "Poison Headcrab" are used interchangeably by the developers; the name was probably changed during early development for the NPC.
  • The Poison Headcrab appears to be more intelligent in Episode Two. When shot, they will almost always run unless they are in the process of leaping. This also applies in any games after the 2010 update. In older versions, the Poison Headcrab used to flee only when ambushed and rushed recklessly at enemies when spotted.
  • If the player is of low enough health, Thrown Poison Headcrabs can act as a last ditch effort to obtain health as the amount HEV recovers is always the same, but this strategy is risky and is best suited when no enemies are around.
  • Although Poison Headcrabs appear in Half-Life: Alyx in great numbers, Poison Zombies do not appear at all.
  • Poison Headcrabs are the toughest of their species in Half-Life 2. While both normal and fast headcrabs die in 2 shots from a pistol, poison headcrabs can take multiple shots and up to 10 on Hard difficulty.


Warning Hiss Scream


List of appearances[]