A headcrab is a fiction

Fiction

Fiction is the form of any narrative or informative work that deals, in part or in whole, with information or events that are not factual, but rather, imaginary—that is, invented by the author. Although fiction describes a major branch of literary work, it may also refer to theatrical,...

al alien

Extraterrestrial life

Extraterrestrial life is defined as life that does not originate from Earth...

 parasitoid

Parasitoid

A parasitoid is an organism that spends a significant portion of its life history attached to or within a single host organism in a relationship that is in essence parasitic; unlike a true parasite, however, it ultimately sterilises or kills, and sometimes consumes, the host...

 found in the Half-Life

Half-Life (series)

The Half-Life series of video games share a science fiction alternate history. Nearly all of the games are first-person shooters on the GoldSource or Source engines, and most are linear, narrative, single-player titles....

video game series created by Valve Software. They are the most numerous and arguably most iconic aliens in the series.

Overview

Headcrabs are parasitic lifeforms roughly 2 foot (0.6096 m) long. Headcrabs have rounded bodies with four legs for movement; two long clawed legs at the front, and two stubby legs at the back. Their pair of large frontal claws are for attacking prey, and as additional support when standing still. Under the headcrab's body is a large rounded mouth surrounded by pointed rigid flesh with sharp claw-like beaks.

The design of the headcrab changes between Half-Life

Half-Life

Half-Life is a science fiction first-person shooter video game developed by Valve Corporation, the company's debut product and the first in the Half-Life series. First released by Sierra Studios, the game was also released for the PlayStation 2. In Half-Life, players assume the role of Dr...

 and Half-Life 2

Half-Life 2

Half-Life 2 , the sequel to Half-Life, is a first-person shooter video game and a signature title in the Half-Life series. It is singleplayer, story-driven, science fiction, and linear...

. 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

Watermelon

Watermelon is a vine-like flowering plant originally from southern Africa. Its fruit, which is also called watermelon, is a special kind referred to by botanists as a pepo, a berry which has a thick rind and fleshy center...

. Half-Life and Half-Life 2 also oppositely depict the headcrab's tolerance to water and toxins: headcrabs in Half-Life can swim in water but die in toxic environments, while headcrabs in Half-Life 2 drown within seconds in deep water but easily survive in contaminated pools.

Physically, headcrabs are fairly 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 surprising distances and heights to catch their prey. Headcrabs seek out larger human hosts, which are converted into zombie

Zombie

Zombie is a term used to denote an animated corpse brought back to life by mystical means such as witchcraft. The term is often figuratively applied to describe a hypnotized person bereft of consciousness and self-awareness, yet ambulant and able to respond to surrounding stimuli...

-like mutants that attack any living thing they can find. The converted humans are far more resilient than an ordinary human would be and inherit the headcrab's resilience toward toxic and radioactive materials. Headcrabs and/or 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, vortigaunt

Vortigaunt

Vortigaunts are a fictional extra-dimensional species in the Half-Life series by Valve Corporation. In Half-Life and its three expansions, Vortigaunts are frequently encountered by the player as hostile non-player characters...

s, barnacles and antlions will all eat headcrabs and vortigaunts can be seen cooking them on several occasions.

Behavior

Headcrabs are often found in dark areas, usually lying in wait in dark corners and ventilation shafts

Ventilation (architecture)

Ventilating is the process of "changing" or replacing air in any space to provide high indoor air quality...

. In more open environments, headcrabs bury themselves in the ground to hide, then climb out to the surface and attack when a victim draws near. Headcrabs are often seen clustered in groups to make up for their individual weakness. They pursue their prey with single-minded determination, never fleeing despite the death of fellow headcrabs or any other dangers. Conversely, however, headcrabs attached to a human may abandon their host should it be severely wounded.

Headcrabs can produce a variety of vocalizations. When they are not hunting, headcrabs usually emit squeaks and fairly quiet, repetitive calls while gently swaying their bodies back and forth until they have sight of a host. When attacking, headcrabs emit a sharp, shrill shriek as they leap toward their victims.

Variants

While the original Half-Life has only one type of headcrab (not counting the Baby Headcrab), identified by its mottled tan-colored skin and reddish legs, Half-Life 2 introduces two more versions, the fast headcrab and the poison headcrab. These versions are more dangerous than their ordinary counterparts.

Fast Headcrab

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 and, like the headcrab itself, are much faster than ordinary zombies. It also makes the same shriek that their standard cousins make.

Poison Headcrab

The poison headcrab (also known as the black headcrab or venomous headcrab) is slightly larger than its counterparts with dark sage-green-colored skin (sometimes with a wet shine, attributable to a lighting problem with Valve Corporation

Valve Corporation

Valve Corporation is an American video game development and digital distribution company based in Bellevue, Washington, United States...

's Source engine) and thick hairs on the joints of its 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

Rattlesnake

Rattlesnakes are a group of venomous snakes of the genera Crotalus and Sistrurus of the subfamily Crotalinae . There are 32 known species of rattlesnake, with between 65-70 subspecies, all native to the Americas, ranging from southern Alberta and southern British Columbia in Canada to Central...

'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 incinerate than the other types.

Poison headcrabs get their name from the neurotoxin

Neurotoxin

A neurotoxin is a toxin that acts specifically on nerve cells , usually by interacting with membrane proteins such as ion channels. Some sources are more general, and define the effect of neurotoxins as occurring at nerve tissue...

 they carry, which reduces the player's health

Health (gaming)

Health is a game mechanic used in role-playing, computer and video games to give value to characters, enemies, NPCs, and related objects. This value can either be numerical, semi-numerical as in hit/health points, or arbitrary as in a life bar....

 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 the 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.

Headcrab zombie

A headcrab's primary goal is to attach to the head of a suitable host

Host (biology)

In biology, a host is an organism that harbors a parasite, or a mutual or commensal symbiont, typically providing nourishment and shelter. In botany, a host plant is one that supplies food resources and substrate for certain insects or other fauna...

 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

Zombie

Zombie is a term used to denote an animated corpse brought back to life by mystical means such as witchcraft. The term is often figuratively applied to describe a hypnotized person bereft of consciousness and self-awareness, yet ambulant and able to respond to surrounding stimuli...

-like being known as a headcrab zombie, referred to as a "necrotic" by the Combine Overwatch. The host lies dead for a while then rises and attacks any living species.

The headcrab's alien physiology

Physiology

Physiology is the science of the function of living systems. This includes how organisms, organ systems, organs, cells, and bio-molecules carry out the chemical or physical functions that exist in a living system. The highest honor awarded in physiology is the Nobel Prize in Physiology or...

 causes various mutation

Mutation

In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...

s in its host, giving it massively oversized claws, increased strength, and what appears to be a sharp-toothed "mouth" that bisects the victim's chest cavity from neck to groin. In Half-Life 2, their appearance is slightly different; the "teeth" of the mouth are clearly revealed as protruding ribs: a ripped open chest cavity and no sternum

Sternum

The sternum or breastbone is a long flat bony plate shaped like a capital "T" located anteriorly to the heart in the center of the thorax...

. In Half-Life, zombies can be seen tearing flesh from corpses and feeding it into their "mouth". The Headcrab stays attached to the zombie even when the zombie dies. In Half-Life 2, headcrab zombies are capable of surviving even if they are severed at the torso, simply dragging themselves along the ground with their arms. Headcrab zombies signal their presence through various muffled groans and grunts, sometimes mixed with agonized screams. The Headcrab dies with the zombie if the player aims for the head.

Like standard headcrabs, both fast headcrabs and poison headcrabs are capable of attaching to a host's head, although these headcrabs 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.

Blasting the Headcrab off any zombie type will reveal that the person's head has been bent back abnormally, and regardless of type, the zombie's mouth is open in a frozen scream. This, coupled with the muffled pleas and screams emitted by the zombie, indicates that the zombie is (at least partially, but most likely fully) aware of their state, but powerless to fight the impulses from the Headcrab, and presumably in constant and unimaginable pain.

Standard headcrab zombie

When a standard headcrab successfully attaches to a host, the host becomes a standard headcrab zombie. The torso of the host is open and the organs can be seen. In Half-Life 1 the player can see the texture of the host's skull on the headcrab. However, this is removed in other 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. The hosts are left alive during the mutation, being left entirely aware of their horrific situation. The host body is in an unconscious state immediately after infestation, and after a while, rise to attack.

Gonome

The gonome is apparently the next step of a standard headcrab zombie's mutation. It is larger, stronger, much faster and more intelligent than "ordinary" zombies; it also produces a stomach acid that the creature can retrieve from its chest "maw" and throw as a weapon. Gonomes appear only in the expansion pack

Expansion pack

An expansion pack, expansion set, or supplement is an addition to an existing role-playing game, tabletop game or video game. These add-ons usually add new game areas, weapons, objects, and/or an extended storyline to a complete and already released game...

 Half-Life: Opposing Force

Half-Life: Opposing Force

Half-Life: Opposing Force is an expansion pack for Valve Software's science fiction first-person shooter video game Half-Life. The game was developed by Gearbox Software and Valve Corporation and published by Sierra Entertainment on November 1, 1999. Opposing Force is the first expansion for...

, which was created by Gearbox rather than Valve.

Fast headcrab zombie

When a fast headcrab attaches to a host, it produces a fast headcrab zombie. These zombies are stripped of their outer skin, some body tissue

Biological tissue

Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. These are called tissues because of their identical functioning...

, and most or all organs

Organ (anatomy)

In biology, an organ is a collection of tissues joined in structural unit to serve a common function. Usually there is a main tissue and sporadic tissues . The main tissue is the one that is unique for the specific organ. For example, main tissue in the heart is the myocardium, while sporadic are...

, leaving large parts of the victim's skeleton

Human skeleton

The human skeleton consists of both fused and individual bones supported and supplemented by ligaments, tendons, muscles and cartilage. It serves as a scaffold which supports organs, anchors muscles, and protects organs such as the brain, lungs and heart....

 exposed. Fast headcrab zombies can run at great speeds and have the unique ability to jump and rapidly climb rain gutters. They also move on all four limbs, but stand on two legs when attacking a victim. Fast zombies betray their presence with several vocalizations. In Half-Life 2: Episode Two, a fast zombie can be seen jumping on the front of the players vehicle, and melee attacking until Alyx Vance kicks it off. Despite their speed and physique, fast zombies are much weaker than ordinary zombies in terms of damage they inflict, though they have the same health as standard zombies. In Episode Two, fast zombies also come in a torso-only variant.

Poison headcrab zombie

Poison headcrabs produce the poison headcrab zombie - a bloated, reddish/purplish, slow-moving and hunched-over "carrier" for several more poison headcrabs. A fully loaded zombie of this type carries four headcrabs, including the host's controller. It is the strongest and most resilient form of headcrab zombie in terms of damage capability and overall health (it takes three crossbow shots just to kill one poison headcrab zombie, but only one to kill an Overwatch soldier) - but also the slowest. A poison zombie reveals its presence with its distinctive, strangled, heavy breathing and muffled moans. Like other zombies, it tries to beat its prey to death, but its most dangerous weapon is the extra poison headcrabs it carries, which it can throw at the player with an elephant-like bellow.

Zombine

Half-Life 2: Episode One

Half-Life 2: Episode One

Half-Life 2: Episode One is the first in a series of episodes that serve as the sequel for the 2004 first-person shooter video game Half-Life 2. It was developed by Valve Corporation and released on June 1, 2006. Originally called Half-Life 2: Aftermath, the game was later renamed to Episode One...

introduces the Zombine, a variation on the regular headcrab zombie created from "former" Combine Overwatch soldiers. Alyx Vance

Alyx Vance

Alyx Vance is a non-player character in Valve's 2004 first-person shooter computer game Half-Life 2, and its following episodes: Half-Life 2: Episode One and Half-Life 2: Episode Two...

 coins the term "Zombine" for them as a portmanteau of "zombie" and "Combine". The introduction of the Zombine enemy 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.

A Zombine can be identified by the distinct Combine armor it wears, as well as its electronically-filtered moans occasionally mixed with Combine soldier reports, such as "Necrotics inbound" or "Sector is. . . not secure". The body armor of the former officer hides the chest and mouth. Removal of a Zombine's headcrab reveals that most of its head has been removed, leaving only the lower jaw and a small lower portion of the skull. Zombines also lack the elongated claws of their counterparts; though, unlike their standard cousins, have the ability to wield grenades which they run at the player with. Before they throw their grenades, the Zombines (ignorantly) allow the grenades to go off on them.

Lamarr

Introduced in Half-Life 2, Lamarr is a headcrab belonging to Doctor Isaac Kleiner. Having been debeaked, thereby eliminating her ability to attach to and control a host, Lamarr has been rendered into a semi-tame pet for Kleiner and a nuisance to anyone else with whom she comes into contact. Lamarr is named after the late 1930s actress and inventor Hedy Lamarr

Hedy Lamarr

Hedy Lamarr was an Austrian-American actress celebrated for her great beauty who was a major contract star of MGM's "Golden Age".Lamarr also co-invented – with composer George Antheil – an early technique for spread spectrum communications and frequency hopping, necessary to wireless...

, as evidenced when Dr. Kleiner alternatively calls her Hedy in the conclusion of the chapters A Red Letter Day and Entanglement.

Lamarr serves as the catalyst for the first few chapters of the single-player campaign in Half-Life 2. When Gordon Freeman

Gordon Freeman

Gordon Freeman is a fictional character and the main protagonist of the Half-Life video game series. He is a theoretical physicist who finds himself thrust into a battle for survival against both alien and human forces. Throughout the series, Gordon must prevail in hostile situations despite...

 attempts to use Dr. Kleiner's teleporter, Lamarr jumps from a vent and damages it while Gordon's teleport is in progress, teleporting him all over the city, including Dr. Breen's office in the Citadel. In the end, Gordon winds up just outside of the lab, with no way back in. This forces Gordon to proceed on foot once the malfunction subsides. When Alyx and Gordon return to the lab some time later, Lamarr escapes her cage, and Alyx has to stay behind to help Kleiner catch her, as Kleiner refuses to leave without her. Lamarr makes her final appearance in Half-Life 2 after the credits, dropping down into a black background and then leaping toward the screen as part of a stinger sequence

Post-credits scene

A post-credits scene is a short clip that appears after some or all of the closing credits of a film have run...

. Lamarr is safe and sound in Episode One, where she makes a brief cameo appearance, causing further mischief to Dr. Kleiner during his unedited evacuation broadcast in City 17. She makes yet another appearance in Episode Two, where the player can see her climb into Dr. Magnusson's rocket, which is launched shortly before the end of the game. Seconds before the launch, Dr. Kleiner notes a payload anomaly of approximately 8.5 pounds, suggesting that Lamarr has been launched into the portal.

Use as biological weapons

While headcrabs are merely wild parasites in Half-Life, Half-Life 2 shows that 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

Half-Life 2: Lost Coast

Half-Life 2: Lost Coast is a small additional level for the 2004 first-person shooter video game Half-Life 2. Developed by Valve Software, it was released on October 27, 2005, through the Steam content delivery service as a free download to owners of the Microsoft Windows version of Half-Life 2...

) 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.
Headcrab shells commonly carry standard headcrabs and fast headcrabs, as can be seen throughout Half-Life 2; poison headcrabs are only seen emerging from headcrab shells during the church battle in Half-Life 2: Lost Coast and in the Exit 17 chapter of Half-Life 2: Episode One

Half-Life 2: Episode One

Half-Life 2: Episode One is the first in a series of episodes that serve as the sequel for the 2004 first-person shooter video game Half-Life 2. It was developed by Valve Corporation and released on June 1, 2006. Originally called Half-Life 2: Aftermath, the game was later renamed to Episode One...

. The only two examples in Half-Life 2 are where the player can enter a house which has been bombed by a headcrab shell during the chapter Highway 17 (searching the house will reveal several poisonous headcrabs and a poisonous headcrab zombie, but no other types, indicating that the shell contained poison headcrabs) and in the Route Kanal level, where the player can find multiple pods lying in a fenced area. Nearby, there are headcrab zombies and dead rebels, suggesting that the headcrabs are dangerous and giving the player an idea of what they do. The number of headcrabs in a missile varies between species of headcrab.

Reception

The poisonous head crab 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.

Merchandise

Due to popular request, Valve released a plush

Plush

Plush is a textile having a cut nap or pile the same as fustian or velvet.Originally the pile of plush consisted of mohair or worsted yarn, but now silk by itself or with a cotton backing is used for plush, the distinction from velvet being found in the longer and less dense pile of 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, though has been brought back on several occasions. 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.

Appearances in other titles

A Headcrab is an unlockable character in the PC and Mac version of Super Meat Boy

Super Meat Boy

Super Meat Boy is an independent video game designed by Edmund McMillen and Tommy Refenes and developed by Team Meat. It is the successor to McMillen and Jonathan McEntee's October 2008 flash game Meat Boy. Super Meat Boy was released on the Xbox 360 through Xbox Live Arcade in October 2010, on...

as an exclusive character for those who purchase the game from Steam

Steam (content delivery)

Steam is a digital distribution, digital rights management, multiplayer and communications platform developed by Valve Corporation. It is used to distribute games and related media online, from small independent developers to larger software houses...

.

A Headcrab helm was included in the April 1, 2011 event in Vindictus as an exclusive.