Headcrab

Headcrabs are depicted as parasitic lifeforms roughly 2 feet (0.61 m) long.[1] The common headcrab variant has rounded bodies with four legs for movement, two of which are long clawed legs at the front and two stubby legs at the back. Their pair of large frontal claws are for attacking, and as additional support when standing still. Under the headcrab's body is a large rounded mouth surrounded by mangled, rigid flesh with a sharp claw-like beak.

Physically, headcrabs are frail: a few bullets or a single strike from the player's melee weapon being sufficient to dispatch them. They are also relatively slow-moving and their attacks inflict very little damage. However, they can leap long distances and heights. Headcrabs seek out larger human hosts, which are converted into zombie-like mutants that attack any living lifeform nearby. The converted humans are more resilient than an ordinary human would be and inherit the headcrab's resilience toward toxic and radioactive materials. Headcrabs and headcrab zombies die slowly when they catch fire. The games also establish that while headcrabs are parasites that prey on humans, they are also the prey of the creatures of their homeworld. Bullsquids, Vortigaunts, barnacles and antlions will all eat headcrabs and Vortigaunts can be seen cooking them in several locations in-game.

While the original Half-Life only contains one type of headcrab, Half-Life 2 introduced two major variations: fast headcrabs and poison headcrabs. Headcrab zombies also receive these variations in Half-Life 2.

The Gonarch is a massive, heavily armored version of a headcrab that appears only once as a boss fight towards the end of Half-Life in Xen. The Gonarch appears to act as a sort of hive queen, endlessly spawning infant headcrabs from a bulbous fleshy sack located on its underside. Unlike other types of headcrabs, the Gonarch lacks a mouth on its underside, suggesting it is unable to zombify a host.

The fast headcrab is a faster, more spider-like version of the ordinary headcrab. Its skin is slightly lighter, and it has long, spider-like legs that allow it to move much faster and climb on walls (first demonstrated in Half-Life 2 in Ravenholm). It does not have a beak like the other varieties, instead using the sharp talons at the ends of its legs to latch to hosts. The zombies it creates are stripped of most of their flesh and muscle. When a fast headcrab is shot off the zombie itself it will reveal a completely bare skull with no tissue, which suggests that the fast headcrab completely takes over control of the host's muscles and nervous system and furthermore becomes the potential brain for the host/zombie. The resulting zombies are, like the headcrab itself, much faster than ordinary zombies. It also makes the same shriek that their standard cousins make.

The poison headcrab (also known as the black headcrab or venomous headcrab) is slightly larger than its counterparts with dark sage-green-colored skin and thick hairs on the joints of its body and inward-bending legs. To distinguish it further, it has white bands that encircle its knee joints, wider legs, and a more flattened body, giving it a generally more crab-like appearance. It also makes a chirp at range and a hissing-rattling similar to that of a rattlesnake's tail when it detects a viable host. Immediately before pouncing, they emit a loud, distinctive shriek. There is also a whipping noise as they pounce. Unlike the other headcrabs, the poisonous headcrab has some survival instinct, as it will retreat when injured. Although it is the slowest-moving version of the headcrab when calm, it can outpace an ordinary headcrab when retreating. Another difference is that the poison headcrab takes a longer time to burn to death than the other types. Poison headcrabs get their name from the neurotoxin they carry, which reduces the player's health to one point instantly on contact, meaning that minimal additional damage can easily kill the player. Gordon's HEV suit provides an antidote that will restore the missing health over a short period, minus the damage caused by the attack itself. While this makes a single poisonous headcrab unable to fully kill Gordon, it can make survival much more problematic if other enemies are present. Half-Life 2: Raising The Bar notes that play-testers would prioritize poison headcrabs as targets, regardless of any other present dangers. They will group together on a single host once one is found: the attacking poison headcrab controls the host, while the others use the new host as transportation, having it throw them at new victims. (It is also possible that these additional headcrabs are produced by the host human as a method of reproduction on the part of the primary headcrab).

A headcrab's primary goal is to attach to the head of a suitable host using its mouth (typically covering the face and most of the head). The headcrab then burrows its claws and hind legs into the host and opens up portions of the skull with its mouth, incorporating parts of its biological workings with the motor cortex of the host's nervous system. The victim is thus taken over by the headcrab and mutated into a mindless zombie-like being known as a headcrab zombie, referred to as a "necrotic" by the Combine Overwatch.

Once the headcrab has converted a host into a headcrab zombie, the torso of the host is open and the organs can be seen. In the first Half-Life the player can see the texture of the host's skull on the headcrab. However, this was removed in future installments. They are slow-moving but powerful, using their claws to beat their victims to death. They moan almost constantly, and growl when they detect prey. In Half-Life 2, they can swat loose objects when they run into them, creating potentially lethal projectiles. Half-Life 2 also introduced still-moving zombies which are severed at the waist and crawl toward the player using their arms. Host bodies are in an unconscious state immediately after infestation, and after a while, rise to attack.

There are six main variants of the headcrab zombie, the "standard zombie", "fast headcrab zombie", "poison headcrab zombie", "armored zombie", the "Gonome", and "Zombine", or Combine Zombie. These have multiple differences from each other and the normal headcrab zombie. As their names would imply, the fast and poison headcrab zombies are created when a fast headcrab or poison headcrab respectively attach to a host. The Gonome is unique in that it is a more aggressive and armored mutation of a standard zombie. The Zombine is created when a headcrab zombie is created from "former" Combine Overwatch soldiers. Alyx Vance coins the term "zombine" for them as a portmanteau of "zombie" and "Combine". The introduction of the Zombine was meant to indicate that, in the wake of the devastation caused by the player in Half-Life 2, what was once a valuable weapon in the Combine arsenal is now just as dangerous to them as it is to regular humans. Along with being able to move faster than normal zombies, zombines also have the unique ability to pull out a live grenade and charge the player, killing themselves in the process.

It is as yet unclear as to what specific function in the Headcrab ecology or reproductive cycle the zombification process serves.

Half-Life: Alyx introduces a new variation whose back is covered by a bullet-proof shell with dark bulbs and some thick spikes on it. To fight one effectively, the player must target the creature's weak underbelly when the opportunity presents itself, such as when the crab balances on its hind legs in preparation for a jump, or when it lands on its back after jumping, after which it can take a few seconds for the headcrab to recover its posture. A single pistol hit to the exposed underbelly is commonly enough to kill the creature.

Headcrabs are one of the first enemies introduced in Half-Life. They are frequently encountered by players throughout Half-Life and its three expansions, Opposing Force, Blue Shift and Decay. They also see appearances in the official port of Half-Life, titled Half-Life: Source, as well as the third-party fan modification remake titled Black Mesa. Because the games are remakes or ports, headcrabs play essentially the same role as they do in the original Half-Life.

The design of the headcrab changes between Half-Life and Half-Life 2. Half-Life headcrabs have exposed teeth and intestines at their mouth, while the Half-Life 2 version does not. As such, it is initially apparent that the headcrab only walks with its large front claws and hind legs, while the stubby legs form part of the headcrab's mouth. The headcrabs found in Half-Life are also noticeably smaller than those in Half-Life 2, which have bodies approximately the size of a watermelon. Half-Life and Half-Life 2 also reverses the headcrab's tolerance to water and toxins: headcrabs in Half-Life can swim in water but die in toxic environments, while in Half-Life 2 they drown within seconds in deep water but easily survive in contaminated pools.

Half-Life 2 shows that rather than just wild parasites in Half-Life the Earth-occupying Combine have put them to use as an unstable but effective biological weapon against the human Resistance. A coffin-like missile is filled with headcrabs, and fired from a mortar (as seen in Half-Life 2: Lost Coast) The Combine will bombard distant areas with these missiles and the payload of each shell is released, free to infest or kill nearby victims without risk to the Combine forces. As is the unfortunate case of the devastated town Ravenholm, repeated bombings can neutralize entire towns and cities in a short span of time.

Half-Life 2 also featured the first appearance of Dr. Kleiner's "pet" headcrab. Referred to as "Lamarr" (after actress and scientist Hedy Lamarr[2]), it serves as an important plot device for a number of scenes in the game, most notably in the second chapter of the game, when, by damaging the teleporter that the player is in, causes it to teleport Freeman outside Kleiner's lab, forcing escape through City 17's canals, and also alerting the combine to the players presence.

• A headcrab is an unlockable character in the Windows, OS X, and Linux versions of Super Meat Boy as an exclusive character for those who purchase the game from Steam.[3]
• A headcrab helm was included in the April 1, 2011 event in Vindictus as an exclusive.[4]
• A headcrab pet was made available in a 2013 update to the action role-playing game Torchlight II.[5] The headcrab pet is available in versions of the game purchased both from Steam and non-Steam storefronts.
• A headcrab cosmetic item was added to Team Fortress 2 in the Summer 2020 Cosmetic Case update.
• A headcrab-like pet was added to the game Among Us around 2019 in the pet bundle.

Due to popular request, Valve released a plush headcrab for sale at the Valve Store.[6] It featured posable limbs, a number of teeth and claws and a gaping maw. For a 2006 Christmas special, along with the re-release of the plush headcrab, fans could buy a headcrab hat, specially designed to give the impression that the wearer is under attack from the parasitic alien.[7] As part of Valve's new marketing relations with the dedicated third-party merchandise selling group, For Fans by Fans, the official Valve website is no longer used as the main platform to sell the aforementioned merchandise. The official headcrab hat is available on the For Fans by Fans' Valve Store section, with its third revision for a new design.[8]

In 2008, the poisonous headcrab was ranked the second most terrifying video game enemy of all time by Cracked due to their venom's ability to drain the players' health to one.[9] In 2011, the poisonous headcrab was ranked at number one on the list of "enemies that scuttle and jump at your face" by GamesRadar.[10]