Headcrab

"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

Headcrabs, often called "head humpers" by Barney Calhoun and "parasitics" by the Combine Overwatch, are the most numerous and arguably iconic aliens of the Half-Life series.

Overview
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 ten feet 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. They appear to have no external sensory organs, including eyes or ears.

The headcrab has several subspecies:
 * The Standard Headcrab - the first headcrab introduced in Half-Life, later seen in its infant form.
 * The Gonarch - a much larger, mature headcrab species which spawns baby headcrabs.
 * The Fast Headcrab - introduced in Half-Life 2, and much faster than standard headcrabs.
 * The Poison Headcrab - apparently toxic, causing more damage to the host. Also introduced in Half-Life 2.

Headcrabs can, apparently, be domesticated, as shown by Lamarr, Isaac Kleiner's pet headcrab, who has been de-beaked, and is "perfectly harmless." Obviously, removing the beak of headcrabs renders them unable to perform their normal function of taking over humans, rendering them harmless or even less aggressive.

"Zombification"
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. It is unknown how long "zombification" takes, although the host appears to retain consciousness for some period of time after the headcrab attaches. However, shortly after the bombardment of Station 6 through the use of Headcrab Shells by the Combine, Gordon Freeman encounters many zombies, showing that the zombification may take from several seconds to minutes.

Combine application


In Half-Life 2, the Earth-occupying Combine alien faction 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 Half-Life 2: Episode One it seems that the Combine have begun to lose control over their bio-weapon; headcrabs begin infecting Combine soldiers, showing the large-scale effects of shelling have caused even Combine-controlled areas to be affected.

Behind the scenes

 * Originally, a device attached to a Gonarch, nicknamed the "Big Momma Pod", was to be used by the Combine for obtaining large numbers of Headcrabs for use in Headcrab Shells.


 * 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 infest, as Zombies are frequently found in conditions that would otherwise be hazardous to their hosts.

Trivia

 * During the Half-Life 2 chapter "A Red Letter Day", Barney refers to Kleiner's "pet" Headcrab Lamarr as a "freakin' head humper", after she causes havoc during Gordon's teleportation.


 * Only the Standard Headcrab can be seen burrowing in and out of the ground.


 * In the Half Life 2 level "Black Mesa East", it's possible to clip into the vortigaunt kitchen by using console commands. In the kitchen you can see that the vortigaunt chefs are cooking headcrabs into a soup.


 * There is a rumor that headcrabs do not grow up to gonarchs. If you look closely at a gonarch's baby, it has sacks on its underbelly just like an adult gonarch. While headcrabs only has a hole on their underbelly.

List of appearances

 * Half-Life: Day One
 * Half-Life
 * Half-Life: Uplink
 * 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