{{Youmayd|the species|the most common subspecies|Classic 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 hosts' nervous system. Can you imagine what the next stage of mutation looks like?|Black Mesa scientist|Half-Life Opposing Force|FileOf1a1 sc05.ogg}}

'''Headcrabs''', often called "'''headhumpers'''" (or "head-humpers") by Barney Calhoun and "'''parasitics'''" by the Combine Overwatch, are the most numerous, and arguably the most iconic, aliens of the Half-Life and Portal universe|''Half-Life'' series.

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

*Headcrabs are fairly small creatures, roughly the size of a pumpkin, which crawl on four legs, and have enough jumping power to leap up to 10 feet (3 meters) in any direction. Their underbelly is almost completely covered by a large, lipless mouth with a hidden "beak" used for feeding and 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.

*Headcrabs were studied at Black Mesa Research Facility|Black Mesa, notably in the Alien Research Labs and the Gamma Labs.

*During the Combine occupation of Earth, Headcrabs appear to have no external sensory organs, including eyes or ears, while the Classic Headcrab had 3 eyes on each side of its body Black Mesa Incident|20 years prior.

*The Classic Headcrab can also be seen burrowing in and out of the ground, but not the other species.

*The Headcrab comes in several subspecies

*The '''Classic 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 Classic 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 Classic 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, apparently, be domesticated, as shown by Lamarr, Isaac Kleiner's pet Headcrab, who has been "de-beaked", and is said to be "completely harmless." Thus, removing the beak of Headcrabs renders them unable to perform their normal function of taking over humans, rendering them harmless and apparently less aggressive.

*It appears that the flesh of both Standard and Fast Headcrabs is edible, at least for 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.



*Headcrabs are a parasitic species, attaching to the host's head and clamping onto their skull using their sharp beak. After breaking through the skull, the Headcrab proceeds to take over its host's motor functions through some unknown biological process, keeping their host alive but helpless through the entire process. As seen in Station 6 in ''Half-Life 2'', it seems to take from several seconds to minutes for a Headcrab to turn humans into Zombies. As no humans live in Xen, the headcrab's homeworld, it would seam unlikely they they would evolve such abilities if there was no hosts. Therefore, it is very likely that they can host Xen creatures as well, such as Vortigaunts. 

*The host appears to retain partial consciousness once the Headcrab has taken control, as Classic Zombies and Zombines retain a certain ability to talk.

*Each Headcrab subspecies affects its host in its own way, producing a Zombie extremely distinct from the other types, in both appearance and behavior.

===Combine application===

{{Main|Headcrab Shell}}

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

In ''Half-Life 2'', the Earth-occupying 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 Development of Half-Life 2 game|''Half-Life 2'' leak files and to be encountered in the Ravenholm mine.Playable Development of Half-Life 2 game|''Half-Life 2'' leak 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.


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

FileHl headcrab.png|Classic Headcrab model, with six eyes (''Half-Life'' version).
FileHeadcrab eyes.jpg|Detail of the 6 eyes on the previous model.
FileHlpsx headcrab.png|Classic Headcrab model, with six eyes as well (PlayStation 2 version).
FileGonarch model.jpg|Gonarch model.
FileHl babycrab.png|Baby Headcrab model.

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

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


FileGordon_NECA.jpg|NECA figure.
FileItem H0301.png|NECA plush.
FileItem headcrab hat.jpg|The original plush hat.
FileItem H0303.png|The new version.

==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''

{{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