Headcrab
A headcrab is a fictional alien parasitoid found in the Half-Life and Half-Life 2 computer game series created by Valve Software. Headcrabs are also referred to as head-humpers by Barney Calhoun and parasitics by the Combine Overwatch. They are the most numerous and arguably most iconic aliens in the series.
At present, there are three different headcrab variations (two of which were introduced in Half-Life 2), all possessing the ability to attach to humans and transhumans to form zombies.
Headcrab
Standard headcrab
Physical description
Often referred to as a normal, original or classic headcrab to distinguish from the other two headcrab species, it is a small creature consisting of a small rounded body with four legs for movement (two stubby legs at the front, obscured by its claws, and two hind legs at the back; see pictured example to the left) and a pair of larger frontal claws for attacking prey or as additional support when standing still. Under the headcrab's body is a large rounded mouth surrounded by pointed flesh (which also includes the headcrab's stubby front legs) with sharp claw-like "beaks." As such, it is initially apparent that the headcrab only walks with its large front claws and hind legs, while the stubby legs only form part of the headcrab's mouth.
Headcrabs also have a mottled tan-coloured skin and reddish legs (although this may simply be blood coloration). The headcrabs found in Half-Life are noticeably smaller than those in Half-Life 2 which have bodies approximately the size of a watermelon. A Valve site selling plush headcrabs [1] describe 6 inches as being quarter-scale, implying that headcrabs are typically 2 feet in length.
Although small, slow-moving, relatively weak on its own, and even seemingly harmless with its tip-toe like gait, the headcrab has the ability to quickly leap long distances using its hind legs, while tilting upwards to face its mouth towards its target, inflicting minor injury with its claws, legs, and teeth. Its main goal, however, is to attach itself onto an appropriate host body.
Curiously, although Half-Life 2's headcrabs are capable of tolerating areas contaminated by toxic waste and radioactivity, they are unable to swim and survive in liquid substances (including water); these traits are reversed in Half-Life. The headcrab's resilience towards toxic and radioactive materials appears to be passed on to the hosts they parasitize, as zombies are frequently found in conditions that would otherwise be hazardous to their hosts.
Headcrabs have been observed to be prey by bullsquids, Vortigaunts, and barnacles. Headcrabs are also hinted in Half-Life 2: Episode One to be consumed by humans, who comment that "they don't taste like crab".
Behavior
Headcrabs have a penchant for lying in wait in dark corners and ventilation shafts. In more open environments, headcrabs are known to bury themselves in the ground to hide, undetected, then climb out to the surface and attack when a victim draws near. Headcrabs are often seen clustered in groups. They will pursue their prey under the most dangerous conditions, moving through dangerous areas or towards hostile prey with little concern for the consequences, even as their fellow headcrabs die in front of them.
Headcrabs can produce a variety of vocalisations. When they are not hunting, headcrabs usually emit squeaks and fairly quiet, repetitive calls while gently swaying their bodies back and forth. When attacking, headcrabs emit a sharp, shrill shriek as they leap towards their victims.
In Half-Life, headcrabs were found to have originated from a giant creature named Gonarch (also known as "Big Mama"), which shares similar physical qualities with headcrabs. Underdeveloped "baby" headcrabs spawn at a rapid rate from a sac that dangles beneath the creature.
Fast headcrab and poison headcrab
New to Half-Life 2 are two previously unseen varieties of headcrabs. It remains to be seen if they come from Xen (as they never appeared in Half-Life) or are result of genetic manipulation of the original form by the Combine.
The first variation is known as a fast headcrab, having longer, thinner, almost spider-like legs, and moves much faster. It is similar to a normal headcrab, but more insect-like. It does not have a "beak" like the other varieties, instead using its sharp talons at the ends of its legs to latch to hosts. It is also capable of clinging to walls and ceilings using its talons, an ability first seen in Half-Life 2: Episode One. Fast headcrabs have been seen being prepared by Vortigaunts as food on more than one occasion.
The second variation, a poison headcrab (also known as black headcrab and venom headcrab), is identifiable by its dark sage green color skin (sometimes with a wet shine) and thick hairs on the joints of its inward bending legs. To distinguish it further it has white bands that encircle its knee joints. Unlike the fast headcrabs, poison headcrab have beaks on their underside like normal headcrabs. 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. 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. A poison headcrab will move slowly and cautiously when maneuvering but will quickly leap with an angry squeal when it has a clear line of sight to the player, and run around frantically when shot at. At walking pace, the poison headcrab is the slowest of the headcrabs, but will run much faster than a normal headcrab if injured. Unlike a normal or fast headcrab, multiple poison headcrab latch onto a single host on multiple parts of its body. Since multiple poison headcrabs infest a single host and are the slowest of the headcrabs, they have adapted by having the host throw several of the headcrabs off itself at a new host.
A poison headcrab's neurotoxin is extremely powerful and hazardous to non-hosts delivered from four fangs on its "mouth." In gameplay it reduces the player's health to 1 hitpoint immediately upon contact, regardless of the current health amount (but health slowly recovers if they remain away from harm for a period of time, due to the HEV suit quickly providing an antidote). Though this neurotoxin is the poison headcrab's primary form of dealing damage; a small amount of health similar to a classic headcrab's attack will be taken off of the player's previous health amount from before the toxin took effect, while also reducing the HEV suit's charge [if any]. Due to this, it is extremely difficult for even a large group of poison headcrabs to kill the player, but this does make the player extremely vulnerable to other forms of damage, such as ballistics, explosives, or other types of headcrabs. If a player is playing on either easy or normal difficulty, poison headcrabs can actually be a very effective tool for the player if he is low on life since, no matter how low the player's life is, it will be fully restored after the antidote has been fully administered.
While appearing similar to the original headcrab, both headcrab variations differ in a sense that they strictly use their four longer limbs for movement, attacking and standing, as opposed to the generally shorter limbs from the original headcrab.
Headcrab zombie
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 or the whole of the head), and burrow its claws and hind legs into the host, whereupon it takes control over its victim's body, rendering the unfortunate individual a mindless zombie-like being.
The headcrab attaches itself on top of the head, where it opens up portions of the skull with its mouth (there is no animation showing a headcrab zombie with the entire skullcap missing, so it is assumed that the headcrab does not actually take off the skull covering). By incorporating parts of its biological workings with the motor cortex of the host's brain, it is able to utilize all of the motor functions of the host. However, the host's thought processes are seemingly undisturbed, and therefore it is assumed that the host is actually alive while being possessed by a headcrab, and worse yet, fully aware of its horrific fate. One could assume this due to the amount of screaming that is done by the infected host, which is muffled at all times by the presence of the headcrab (a good example is when one is on fire).
Interestingly, no Xen species are seen infested with headcrabs. Indeed, the physical makeup of the headcrab, and its apparent need to clamp on the "head" of a humanoid makes it unlikely that it is capable of "zombifying" other creatures of Xen. As such, it is unclear how headcrabs subsist in their native environment, and even more unclear how this ability evolved. Lamarr, Dr. Kleiner's pet headcrab, is fed watermelons, although another one is seen to attack a crow later on in the scene, which suggests that headcrabs are omnivores.
Like standard headcrabs, both fast headcrabs and poison headcrabs are also capable of attaching to a host's head, although these headcrabs each induce different forms of mutations on their hosts and the resulting zombies employ different strategies of attack. An unusual characteristic of both zombie variations is that only three middle fingers of the five on each zombie's hands develop into claws, compared to all the fingers on a standard headcrab zombie. In addition, neither two variants have a describable "maw" nor the chest cavity that normal headcrab zombies possess, although fast zombies do have cracked rib cages and seemingly no internal organs, creating a hollow space.
Standard headcrab zombie
When a headcrab successfully attaches to a host, the host becomes a "headcrab zombie", or "necrotic", as it is referred to by the Combine Overwatch. The headcrab's alien physiology causes various "mutations" to rapidly manifest in its host, such as elongated claws, increased strength, and a sharp-toothed, sideways mouth that bisects the victim's chest cavity from neck to groin. This giant mouth has inspired the nickname "Mawmen". It should be noted that in Half-Life 2, their appearance is different; instead of this chest "maw", they appear to be protruding ribs: a ripped open chest cavity and no sternum. The official Prima game guide for Half-Life 2 still mentions the "Mawmen" nickname, however. The zombies do not appear to retain any of their former intelligence, blindly pursuing their prey, oblivious to danger. In Half-Life 2 they gain the ability to throw objects, even health pickups and ammo, when they run into them. Some of the zombies encountered in the game have no body below their waists; they crawl around with their arms and swat at the player. An overlooked effect that signals a zombie's presence in the run-down areas of City 17 is the buzz of flies, showing that the corrupted body of the victim is rotting.
In most cases, a headcrab remains attached to its host until destroyed, although in Half-Life 2, they have the ability to detach from the host if it is wounded significantly. Removal of the headcrab reveals that the host's face and head has been eaten away by the creature; the degree of such damage on these areas depends on the type of headcrab in control. In Half-Life 2, horrified sounds emanating from headcrab zombies imply that, while wounded to a point which would make loss of headcrab control fatal, the host creature is at least partially aware of its horrific situation. Playing parts of a victim's sound file backwards produces extremely disturbing yells of pain. The reversed cries have been interpreted as "God help!", "Kill me!", "Why! Why! Why!" and "Help me!".
The artistic inspiration for headcrabs appears to be the human form of John Carpenter's The Thing.
Gonome
The gonome is apparently the next step of a standard headcrab zombie's "mutation". It is larger, stronger, and more intelligent than "ordinary" zombies; it also produces a volatile saliva (similar to that of a bullsquid) that the creature can retrieve from its chest "maw" and throw as a weapon. Gonomes can create lairs, or "nests", for themselves with enough time. Officially, gonomes appear only in the expansion pack Half-Life: Opposing Force.
Fast headcrab zombie
Fast headcrabs produce fast zombies, stripped of their outer skin, some body tissue and most or all organs (revealing large parts of the victim's skeleton), along with the standard elongated claws. These zombies are fast, agile, and have the ability to leap long distances and climb quickly despite the absence of most of their muscle tissue. Fast zombies also move on all four limbs, but stand on two legs, as do the other types of headcrab zombies. Unused animations in Episode One and trailers for Episode Two show that these fast zombies will have the ability to jump and latch onto moving vehicles, allowing them to attack the passengers inside. This is shown during a sequence in Half Life 2: Episode Two, where the player is attacked by a fast zombie during the drive to White Forest. Another unused model in Episode One shows the crawling upper torso of a fast zombie, similar to regular zombie torso enemies, implying that fast zombies can also survive being cut in two and will still continue to attack. Their torsos are, in fact, used in Episode Two, and crawl along the ground at about the same speed as a Zombine's run. A fast headcrab zombie's usual method of attacking, when given a clear distance between it and its prey, is to leap forward several yards while releasing a horrific shriek and clawing/ramming its victim into the dirt.
Poison headcrab zombie
Poison headcrabs produce a bloated, reddish/purplish, slow-moving, and hunched-over "carrier" zombie, referred to as a poison zombie, that seems to have even more endurance and resilience to damage than its brethren. Usually seen encumbered with several other poison headcrabs hitching a ride atop it, when this zombie senses an enemy, it hurls these hitch-hiking headcrabs with great distance and accuracy, although the headcrabs may jump off by themselves. Carrier zombies are not, themselves, poisonous; if one has no more headcrabs to hurl, it will attack only with its claws like a traditional zombie. Their presence can be detected by their distinctive strangulated heavy breathing or muffled moans.
Zombine
Half-Life 2: Episode One depicts a new type of headcrab zombie – a Combine Zombie, or Zombine – created as a result of headcrab infestation on a transhuman Combine soldier. Only Zombines controlled by normal headcrabs appear in Episode One and Episode Two. Alyx coins the term "Zombine" as a portmanteau of "Zombie" and "Combine".
Zombines move faster than normal headcrab zombies (capable of short sprints), but slower than the fast variety. They are stronger than their normal counterparts (they take three normal shotgun shots to kill) likely due to their intact battle armor. Zombines will pull out grenades using them as a club, though unlike uninfected soldiers, they will continue holding onto them until it explodes. This can be easily stopped by using the gravity gun to pull the grenade out of its hands and punt it away. Zombine groans are filtered through the soldier's vocoder (how this occours despite the fact that the Zombine has a total lack of skull and mask is a mystery). The Zombines also manifest at least partial awareness of their state, much like regular Zombies. This is evidenced by its "speech", which is composed of Zombie growls and Combine soldier reports, such as "Necrotics inbound" or "Sector's not secure".
Removal of a Zombine's headcrab reveals that, aside from the lower jaw and small lower portion of skull, no head or helmet remains on the soldier's corpse. The official Prima strategy guide for Episode One indicates that the lack of a head is meant to be an intentional mystery.
Lamarr
In Half-Life 2, the catalyst for the first few chapters of the single player campaign is the pet headcrab belonging to Doctor Isaac Kleiner, Lamarr, who damages Kleiner's teleporter and forces Gordon Freeman to travel on foot. Lamarr is named after the late 1930s actress and inventor Hedy Lamarr, as evidenced by a line issued by Dr. Kleiner just after Lamarr jumps onto the working teleporter during "A Red Letter Day" chapter, and at the end of the chapter "Entanglement". In the latter, as Gordon Freeman, Alyx Vance, and Dr. Kleiner are attempting to evacuate Dr. Kleiner's lab after it is discovered that the Combine are making an offensive sweep of the area, Dr. Kleiner states that he wishes to find and save his pet headcrab (which he is unable to find, after Lamarr peeks alongside Dr. Kleiner at Alyx and Gordon when the latter arrive at Kleiner's lab, backs off and disappears) before they leave. Alyx attempts to rebut him by telling him that there are many other headcrabs to use as a pet, and he replies by saying "There's only one Hedy". Lamarr makes her final appearance in Half-Life 2 after the credits, dropping down into a black background and then leaping towards the screen as part of a stinger sequence. Lamarr is safe and sound in Episode One, where she makes a brief cameo appearance, causing further mischief to Dr. Kleiner during his live and unedited evacuation broadcast in City 17 (though the question of how she found her way back to Dr. Kleiner is left unanswered). She makes yet another appearance in Episode Two, climbing into a rocket and shaking in fear upon seeing Freeman. It is not made clear if Lamarr was in the rocket when it was launched; However it is likely due to the fact that Freeman can close and seal the hatch to the rocket, and that in the control room there is a reference to a "payload anomaly of 8.5lbs" just prior to launch which may be explained by her presence.
Lamarr demonstrates that it is possible to disable a headcrab's capability to couple and infest a host. Lamarr is said to be "debeaked" by removing the sharp "beaks" surrounding her mouth, removing her ability to cut into a victim's head and assume control. Lamarr's behavior may also be proof of the ability to "tame" a headcrab. Simply being debeaked does not suppress the aggressive, parasitic nature found in all headcrabs. Lamarr does still run around as shown when she is first met: lunging at Barney, then escaping into the vent shaft. Kleiner also states that "The worst she might do is attempt to couple with your head... fruitlessly," behaviour that leads Barney to dub her "freakin' head-humper." Lamarr is seen walking beside Dr. Kleiner and peeking curiously around a corner, showing she is tame to an extent. Although Kleiner refers to Lamarr as a female, whether headcrabs actually have a gender remains unknown.
Combine application
In Half-Life 2, the Earth-occupying Combine alien race is seen utilizing headcrabs as a form of biological weaponry against the Resistance. "Headcrab shells", as they are known, are shells containing several headcrabs, fired from launchers (only one is featured, in Half-Life 2: Lost Coast, but there are likely to be more such launchers), and its payload released into the open shortly after impact, free to infest or kill nearby victims. If released in large numbers, the shells are highly effective in neutralizing a large concentration of Resistance groups, as proven during a visit to the devastated town of Ravenholm. Standard headcrabs and fast headcrabs have been observed emerging from headcrab shells that have been launched, however poison headcrabs have only been seen emerging from unlaunched headcrab shells during Lost Coast and in the chapter Exit 17 of Half-Life 2: Episode One.
The Combine's mechanism for obtaining large numbers of headcrabs for use in these shells was revealed in Half-Life 2's 2003 code leak, in which a model of an amputated Gonarch sac could be found suspended in a Combine-built frame [2]. Officially however, no reason has been given.
Merchandise
In order to fulfill their fans' demand for headcrabs, Valve released a plush headcrab for sale at the Valve Store. It featured posable limbs, a number of teeth and claws and a gaping maw. The headcrab went out of sale within a few months. For a 2006 Christmas special, along with the re-release of the plush headcrab, fans can buy a headcrab hat, specially designed to give the impression that the wearer is under attack from the parasitic alien.
Headcrab-like creatures
The headcrab is vaguely similar to the facehugger in the Alien movies, although their purposes for their hosts are different. The Flood creatures from the Halo video game series are also similar to headcrabs. Remotely similar to the headcrabs, the Flood parasites send needle-like tentacles into the victim's neck to control the victim via the spinal column, though they are filled with flammable gas and explode violently when killed. The headcrab's parasitic ability is also speculated to be inspired by the capability of the Emerald Cockroach Wasp to paralyze and control "zombie" cockroaches, in a manner that could be similar to how a headcrab controls its host [3].
Similar plot devices are used though fiction such as in Ian Livingstone's fighting fantasy book Island of the Lizard King, involving a creature called a "Gonchong" whose proboscis would burrow into the head of a host to control it, Clark Ashton Smith's short story The Vaults of Yoh-Vombis features slug-like creatures that eat away human skulls, then control their victims through neural stimulus; unlike the Gonchong, the headcrab does not actually bury into the skull of the host. In the Star Trek film The Wrath of Khan, Ceti eels are used. In all these examples an animal is used to control the thought and or actions of a human host. Template:Half-Life characters Template:Half-Life enemies