The Poison Headcrab can be identified by its dark skin, bristly hair and red-and-white patterned legs. The creature's dorsal markings are similar to those of a species of orb-weaving spider (Araneus diadematus).
Behavior and skills
At a walking pace, the Poison Headcrab is the slowest of Headcrabs, but panics and runs away if attacked or set on fire. Poison Headcrabs move slowly and cautiously when maneuvering, but leap with incredible speed while releasing an angry squeal when a suitable host is in a clear line of sight. As an ambush tactic, it leaps at and poisons a viable host in an attempt to create a Poison Zombie.
It makes a sound similar to that of a Rattlesnake before attacking. When idle, it can be heard making mouse-like chirping sounds, possibly in an attempt to lure a prey to its location.
It is also one of the only Headcrabs that actively "hunt," whereas other headcrabs will simply wait for their prey.
The Poison Headcrab appears to be the most intelligent Headcrab, possessing enough self-preservation to run away if attacked and attempting to hide if close to death.
The Poison Headcrab delivers its extremely powerful neurotoxin via the four fangs on its chelicerae. In-game, the neurotoxic venom reduces the player's health to 1 immediately regardless of the current health amount. After a short period of time, the HEV Suit will administer an antidote to restore the lost health, with 10 of it being lost from the Headcrab's physical damage.
As of the 2010 update, poison headcrabs are unable to kill the player alone.
Like all other Headcrabs, Poison Headcrabs can latch onto a Human's head and take control of their nervous system, creating a mindless 'Zombie' that submits to the will of the Headcrab. Poison Zombies have a number of key differences from Standard Zombies, including increased health and the ability to carry 3 other Poison Headcrabs on their back.
Poison Headcrabs can be difficult to deal with, as their bite can leave the player vulnerable to other enemies. They also have higher health. Therefore, it is best to focus on these Headcrabs first, before attacking other foes. If there are Barnacles around, the player can lure Poison Headcrabs into their tongues to get a quick kill and conserve ammo. However, Freeman can hit them with the crowbar while it is lunging, and hide while his health regenerates.
The Shotgun is nearly always a one-hit kill at close range. Conversely, the .357 Magnum is a one-shot kill at any range, making it good for eliminating them before entering their range. Poison Headcrabs can be stunned and then killed with 3 blasts from the Gravity Gun. If the player is not interested in using this method, they must keep away from the Headcrab while firing into its body. If they are bitten, they should run away from the Headcrab(s) and let their health recover.
- 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.
- 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").
- 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. However, Alyx Vance and Barney Calhoun regenerate health, and thus 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 the bite of a Poison Headcrab, which does not cause his health to drop to 1. Furthermore, he will not take any damage from this type of 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).
- A Barnacle will instantly die upon eating a Poison Headcrab.
- 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 for post-combat.
- Although Poison Headcrabs appear in Half Life: Alyx in great numbers Poison Zombies do not appear.
List of appearances
- Half-Life 2 (First appearance)
- Half-Life 2: Raising the Bar (Non-canonical appearance)
- Half-Life 2: Lost Coast (Non-canonical appearance)
- Half-Life 2: Episode One
- Half-Life 2: Episode Two
- Half-Life: Alyx