Poison Headcrab

The Poison Headcrab (also commonly known as the black headcrab, named "Venom Crab" by Alyx Vance) 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 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). Gordon's first encounter with this beast is in a dead house in Ravenholm, just before he activates a switch to deactivate an electrical fence in the cobblestone street below.

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 whistling noise.

Venom
The Poison Headcrab delivers its extremely powerful neurotoxin via the four fangs on its "beak". 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.

Contrary to popular belief, it is possible for a Poison Headcrab to kill the player. In order for this to be possible, the player must have 2-10 health remaining; if the player has exactly 1 health, then they cannot die from the Headcrab's attack, even when not under the effect of the poison. Hence, if the player's amount of health ends with 1, then they cannot die from Poison Headcrabs alone.

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.

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.
 * 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, Barney Calhoun, and Father Grigori 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.
 * 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.
 * If one were to guide a Poison Headcrab into a Barnacle's tongue it will eat it, however after eating the headcrab, it will die probably due to its poison.
 * The poison headcrab appears to be the most intelligent headcrab. This is because it will 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. Other headcrabs will 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, and accompanied by other enemies such as Fast Headcrabs, can instantly kill the player. This being the player getting bitten by the Poison Headcrab and simultaneously getting attacked by the Fast Headcrab, this will also work with any other enemy. However, fortunately, they are the rarest headcrab and give plenty of time for the player to move away before attacking.

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