Poison Headcrab

The Poison Headcrab (also commonly known as the black headcrab) is a Headcrab subspecies previously unknown before the Combine invasion. Like its relatives, the Poison Headcrab is able to infest and mutate humans into 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.

Overview
The Poison Headcrab can be identified by its dark colored skin (sometimes with a wet sheen) and thick hairs on the joints of its inward bending, spider-like legs. On the Poison Headcrab's legs are white bands that encircle the knee joints and the creature's dorsal markings are similar to those of a species of orb-weaving spider (Araneus diadematus).

Behavior and skills
At walking pace, the Poison Headcrab is the slowest moving Headcrab, but will panic and run away if attacked. Poison Headcrabs move slowly and cautiously when maneuvering but will 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 will leap at and poison a viable host in the 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 whistling noise.

Venom
The Poison Headcrab delivers its extremely powerful neurotoxin via the four fangs on its "beak". In gameplay, the neurotoxic Headcrab venom will reduce 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 that will restore the lost health, with 10% of it being lost from the Headcrab's physical damage.

Contrary to popular belief, it is possible for a Poison Headcrab to kill the player (however, only in Episode Two. They cannot kill in any way in previous episodes). Though in order for this to happen, the player must have 2-10 health remaining. However, if the player has exactly 1 health, they will not die from the Headcrab's attack, even if they're not under the effect of the poison. This means that, for example, if a player has 41 health, they will not die from the Headcrab if bitten enough times, as they will eventually be left with 1 health. But if the player had, say, 36 health, they will die if bitten enough times.

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 highly risky and very unrewarding. It's better to attack these vicious creatures directly.

The Gravity Gun can stun Poison Headcrabs with two jolts. A third jolt, delivered with sufficient speed, will reduce the Headcrab to a few bloody lumps on the floor. If you are not confident to use this method (it can be hard to aim the Gravity Gun precisely), 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.

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.
 * 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, like any other Headcrab, will die if blasted three times with the Gravity Gun.
 * 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, allowing them to be instantly killed the next time they receive damage. However, Alyx Vance, Barney Calhoun, and Father Grigori all have regenerating health, and thus the Poison Headcrab is less of a threat to them, provided they are not under heavy attack from other enemies.
 * In Half-Life 2, the Poison Headcrab has a minimum distance before it can attack. If the player crouches directly in-front of it, it will not attack but instead crawl backwards to get minimum range to jump.

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