Poison Headcrab

"Watch the headhumpers, Gordon."

- Barney Calhoun

The Poison Headcrab is a venomous Headcrab variant, and one of the three known varieties of Headcrab. Like its relatives, the Poison Headcrab is able to parasitize humans and convert them into Zombies.

Overview
The Poison Headcrab can be identified by its dark green-black 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). Gordon's first encounter with this beast is in a house in ivy bridge.After possessing a host turning it into a poison zombie it will latch on to be carried to another host causing a never ending chain of poison zombies

It is unknown whether Poison Headcrabs are a natural subspecies never encountered on Xen or a result of Combine genetic manipulation of the Standard Headcrab for use in Headcrab Shells.

Behavior and skills
At walking pace, the Poison Headcrab is the slowest Headcrab, but panics and runs away if attacked. Poison Headcrabs move slowly and cautiously when maneuvering but leaps 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. Poison Headcrabs make a sound similar to Rattlesnakes when searching for prey. Also, as another lure, the Poison Headcrab will make a mouse-like chirp.

Venom
The Poison Headcrab delivers its extremely powerful neurotoxin via the four fangs on its chelicerae. In gameplay, the neurotoxic Headcrab venom reduces the player's health to 1% immediately regardless of the current health amount. After a period of time, the HEV Suit will provide an antidote to restore the lost health, with 10% of it being lost from the Headcrab's physical damage.

As of the 2010 update, it appears that Poison Headcrabs alone are indeed incapable of killing the player.

Poison Zombie
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.

Tactics
Poison Headcrabs can be difficult to deal with, as their bite can leave you vulnerable to other enemies. Therefore, it's best to focus on the Headcrabs first, before attacking other foes. If there are Barnacles around, you can lure Poison Headcrabs into their tongues to get a quick kill and conserve ammo. However, this should not be considered a tactic in itself as it can be risky. It's better to attack these vicious creatures directly.

Poison headcrabs can be stunned and then killed with 3 blasts from the Gravity Gun. If you are not confident enough to use this method, you must keep away from the Headcrab while firing into its main body. If you are bitten, run away from the crab(s) and let your health recover.

If you are careful and in a situation which involves small rooms and large amounts of enemies (such as in Ravenholm), you can use your Crowbar to quickly dispatch of headcrabs, and any weapon of choice to kill any zombies in the area.

Trivia



 * 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.


 * In the Half-Life 2 Beta, there was an unused animation "spitattack". This suggests the Poison Headcrab used to have 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").
 * If severely hurt, the Poison Headcrab will attempt to hide or run away from the player, in hopes that it will not be killed. It is also interesting to note that on rare occasions, the Poison Headcrab will ignore the player and try to seek refuge in a corner or secluded area.
 * 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.
 * Father Gregori is the only NPC who are immune to poison headcrab's bite, which doesn't cause his health to drop to 1, however, he will still be hurt if attacked.
 * 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.
 * A Barnacle will instantly die upon eating a Poison Headcrab. However this may not always happen in Half-Life 2
 * The poison headcrab appears to be the most intelligent headcrab, possessing enough self-preservation to run away if attacked and attempt to hide if close to death. It is also one of the only headcrabs that actually "hunt" their prey, whereas other headcrabs will simply wait for their prey.
 * Poison Headcrabs are the strongest headcrab and in some cases the strongest enemy in the game. It is the only enemy able to drop the players health down to critical levels in one shot, which other nearby enemies such as Fast Headcrabs can take advantage of to instantly kill the player. Fortunately, they are the rarest headcrab and give plenty of time for the player to move away before attacking.
 * There is only one sighting of Poison Headcrabs emerging from Headcrab Shells. Although it is implied in areas such as an abandoned building along the coast road, the first and only instance of a Poison Headcrab emerging from a pod is inside a container during the strider battle in the end of Episode One.
 * 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:
 * 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 less aggressive in Episode Two, with when shot, he will almost always run. In older versions, the Poison Headcrab will only run when attacked unaware.

Audio
idle enraged

List of appearances

 * Half-Life 2
 * Half-Life 2: Raising the Bar
 * Half-Life 2: Lost Coast
 * Half-Life 2: Episode One
 * Half-Life 2: Episode Two