{{Youmayd|the species|the most common subspecies|Standard Headcrab}}
{{Headcrab Infobox
| image=FileHeadcrab models.jpg|250px
| name=Headcrab
| affiliation=Xen wildlife
| type=Parasite
| weapons=
| entity=*monster_headcrab (HL)
*monster_babycrab (HL)
*monster_bigmomma (HL)
*npc_headcrab (HL2)
*npc_headcrab_fast (HL2)
*npc_headcrab_poison (HL2)
*npc_headcrab_black (HL2)
| designer=Ted Backman''Half-Life 2 Raising the Bar''
| hidep=yes
{{Quote|Have you ever seen such a magnificent species? These 'crabs' can completely control their host's nervous system. Can you imagine what the next stage of mutation looks like?|Black Mesa scientist|Half-Life Opposing Force}}

'''Headcrabs''', derisively called "'''headhumpers'''" by Barney Calhoun and known as "'''parasitics'''" by the Combine Overwatch, are omnivorous, parasitic creatures. They are widely considered one of the most iconic aliens of the Half-Life universe|''Half-Life'' series.

FileHeadcrab underbelly.jpg|thumb|left|150px|The Standard Headcrab's underbelly.

Headcrabs are small creatures, roughly the size of a pumpkin. They are covered in smooth skin, which varies in color between subspecies, and crawl on four short legs. These legs provide enough jumping power to leap up to 3 metres (10 feet) in any direction. 

Their underbelly is almost completely covered by a large, lipless mouth, with a hidden "beak" used for feeding and for latching onto the skulls of victims. ( below) As seen on Xen in ''Half-Life'', Headcrabs appear to typically be born out of Gonarchs, therefore some Headcrabs may evolve into Gonarchs, and never use a host.

The Headcrab, or at least the Standard Headcrab's natural predator appears to be the Bullsquid. A couple of scenes in Half-Life feature Bullsquids using their ranged attack to kill Headcrabs, who in turn attempt to defend themselves but are killed first. The Bullsquid then comes crawling over to feed on them. Although this behaviour is not seen on Xen in the creatures' naturals habitats, it can still be safely assumed that Bullsquids naturally prey on Headcrabs.

Headcrabs were studied at Black Mesa Research Facility|Black Mesa, notably in the Advanced Biological Research Lab and the Gamma Labs.

During the Combine occupation of Earth, Headcrabs appear to have no external sensory organs, including eyes or ears, while the Standard Headcrab had 3 eyes on each side of its body Black Mesa Incident|20 years prior. The Standard Headcrab can also be seen burrowing in and out of the ground, but not the other species.

The Headcrab comes in several subspecies

*The '''Standard Headcrab''' - the first Headcrab introduced in ''Half-Life'', seen in its infant form near the end of the game. It turns its host into a Standard Zombie, and in some cases a Gonome.
*The '''Gonarch''' - a much larger, mature Headcrab species which spawns baby Headcrabs. Does not use hosts.
*The '''Fast Headcrab''' - introduced in ''Half-Life 2'', and much faster than Standard Headcrabs. Turns its host into a Fast Zombie.
*The '''Poison Headcrab''' - a toxic Headcrab, causing more damage to the host. Also introduced in ''Half-Life 2'', it turns its host into a Poison Zombie.

FileLamarr and Kleiner.jpg|thumb|right|200px|Lamarr and Kleiner.

Headcrabs can be domesticated, as seen with Lamarr, Isaac Kleiner's pet Headcrab. Lamarr has been "de-beaked", and is said to be completely harmless; removing the beak of Headcrabs renders them unable to cut into a host head, rendering them harmless and apparently less aggressive.

It appears that the flesh of both Standard and Fast Headcrabs is edible, at least by Vortigaunts. The former can be seen being prepared by Vortigaunts in Black Mesa East while the latter can be seen being roasted by the All-Knowing Vortigaunt. The poison headcrabs, however, are not edible; if a barnacle eats a poison headcrab, it dies after swallowing the headcrab.



Headcrabs are a parasitic species. Upon sighting a humanoid host, a headcrab will leap for the victim's face and affix itself to the cranium, whereupon they will use their beak to break into the victim's skull. The Headcrab then proceeds to take over its host's motor functions through some unknown biological process. The host will then undergo physical changes, presumably induced through chemical means; although the mutations vary between headcrab subspecies, common changes include the elongation of hands and fingers, reduction or removal of skin and muscle tissue across much of the body, and the exposure of the organs inside the chest cavity. Headcrabs keep their host alive throughout the entire process, helpless and unable to remove the headcrab or resist its control. As seen in Station 6 in ''Half-Life 2'', it apparently takes anywhere from several seconds to several minutes for a Headcrab to turn humans into Zombies.

The host appears to retain partial consciousness once the Headcrab has taken control. Standard Zombies retain a certain ability to talk, always heard as violent cries for help. "Zombines" seem to be able to speak with their vocoders (that is disputed, however). Each Headcrab subspecies affects its host in its own unique way, producing a Zombie extremely distinct from the other types, in both appearance and behavior.

Despite their non-Earth origin, headcrabs appear to be uniquely well-suited for parasitizing human hosts their mouths fit perfectly over a human cranium, and their internal chemistry is compatible with that of humans such that the headcrabs can alter their bodily makeup. It is possible that they were specifically engineered by the inhabitants of Xen as a form of biological warfare, to be used against humanity during the invasion of Earth. It is also possible that they are naturally-occurring creatures, and that they have evolved to parasitize any humanoid host regardless of origin; this would imply that they are capable of parasitizing Vortigaunts, Alien Grunts and other humanoid Xen residents, although no examples of zombies from any of these species are known to exist.

===Combine application===

{{Main|Headcrab Shell}}

FileHeadcrab shell station 6.jpg|left|200px|thumb|Standard Headcrabs emerging from a deployed Headcrab Shell.

In ''Half-Life 2'', the Combine is seen utilizing Headcrabs as a form of biological weaponry against the Resistance. "Headcrab Shells", as they are known, are large mortar shells containing a payload of Headcrabs, which are released on impact, free to infect or terrorize anyone nearby. If used in large numbers, these shells are highly effective in neutralizing a large Resistance base. The effects of large-scale Headcrab shelling are seen during Gordon's visit to the devastated town of Ravenholm, where most inhabitants have been turned into Zombies.

In ''Episode One'' it seems that the Combine have begun to lose control over their bio-weapon; Headcrabs begin Zombine|infecting Overwatch Soldiers, showing that the large-scale effects of shelling have caused even Combine-controlled areas to be affected.

==Behind the scenes==
FileCombine BM Pod.jpg|right|200px|thumb|The Combine Big Momma Pod.

*Originally, a device holding a Gonarch's sack, nicknamed the "Combine Big Momma Pod" a reference to the Gonarch's nickname, was to be used by the Combine for obtaining large numbers of Headcrabs for use in Headcrab Shells,Playable Half-Life 2 Beta|''Half-Life 2'' Beta files and to be encountered in the Ravenholm mine.Playable Half-Life 2 Beta|''Half-Life 2'' Beta Since the device does not appear in the final games, it is unknown so far how the Combine breeds their Headcrabs.

*While the Headcrabs found in ''Half-Life'' and its expansions are able to swim and survive in water but not in areas contaminated by toxic waste and radioactivity, this is reversed in ''Half-Life 2'' and its Episodes, where Headcrabs can be found surviving in toxic areas, and drowning when going into water. The Headcrab's new resilience towards toxic and radioactive materials even appears to be passed on to the hosts they infest, as Zombies are frequently found in conditions that would otherwise be hazardous to their hosts. This may be the results of their adaption to Earth's features, or modifications applied to them by the Combine.

*The Headcrabs in ''Half-Life 2'' cannot attack the player if he is inside a vehicle. They will only rush at the vehicle and attempt to push it, but they end up getting crushed by the vehicle. However, this can be advantageous to Poison Headcrabs since their attack can be very dangerous.


===''Half-Life'' and its expansions===

FileHeadcrab model.jpg|Standard Headcrab model, with six eyes (''Half-Life'' version).
FileHeadcrab eyes.jpg|Detail of the 6 eyes on the previous model.
FileHeadcrab decay model.jpg|Standard Headcrab model, with six eyes as well (''HD'' and ''Decay'' version).
FileGonarch model.jpg|Gonarch model.
FileHeadcrab baby.jpg|Baby Headcrab model.

===''Half-Life 2'' and its Episodes===

FileHeadcrab Standard.jpg|Standard Headcrab model, without eyes.
FileHeadcrab Fast.jpg|Fast Headcrab model.
FileHeadcrab poison.jpg|Poison Headcrab model.

==List of appearances==

*''Half-Life Day One'' {{1st}}
*''Half-Life Uplink'' {{Nc}}
*''Half-Life Opposing Force''
*''Half-Life Blue Shift''
*''Half-Life Decay''
*''Half-Life 2''
*''Half-Life 2 Raising the Bar''
*''Half-Life 2 Episode One''
*''Half-Life 2 Episode Two''

==External links==

*http//www.thinkgeek.com/geektoys/plush/e7f8/?cpg=froogle Headcrab hat

{{Imagecat|Headcrab images}}

CategoryHalf-Life Opposing Force
CategoryHalf-Life Blue Shift
CategoryHalf-Life Decay
CategoryHalf-Life Uplink
CategoryHalf-Life 2
CategoryHalf-Life 2 Lost Coast
CategoryHalf-Life 2 Episode One
CategoryHalf-Life 2 Episode Two
CategoryRecurring themes
CategoryTed Backman designs
CategoryHalf-Life 2 Raising the Bar
CategoryXen creatures

|description=The Leech.
|source=''Half-Life 2'' / ''Half-Life 2 Prima Guide''
|other versions=
|cat artist=
|cat subject=CategorySource model imagesCategoryLeech images
|cat type=CategoryHalf-Life 2 screenshots