Headcrab

"Have you ever seen such a magnificent species? These "crabs" can completely control their host's nervous system."

- Black Mesa scientist

The Headcrab, also referred to colloquially as "head humper" by Barney Calhoun and "parasitic" by the Combine Overwatch, is the most numerous and arguably iconic alien in the series.

Overview
Headcrabs are fairly small creatures, consisting of a rounded body with four legs for movement and a often pair of larger frontal claws for attacking prey or as additional support when standing still. Headcrabs appear to have no external sensory organs, so it is assumed they move about by touch and vibration.

The Headcrab includes several subspecies. The first to be introduced is the Standard Headcrab and the Gonarch in Half-Life. Half-Life 2 updated the Standard Headcrab and introduced two new subspecies, the Fast Headcrab and the Poison Headcrab, along with new Zombies.

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 mortar shells containing several Headcrabs. After impact, their payload of Headcrabs is released into the open, free to infest or kill nearby victims. If used in large numbers, these shells are highly effective in neutralizing a large concentration of Resistance groups. The effects of large-scale Headcrab "shelling" are seen during a visit to the devastated town of Ravenholm.

Behind the scenes

 * Originally, a device attached to a Gonarch, nicknamed "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 radioactivity 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.

Trivia

 * During the Half-life 2 chapter 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. The other variants are presumably incapable of this skill.


 * In a video on Youtube, "Scientist Vs. Headcrab", the player walks up to a room with a window. Inside is a battle going on between a headcrab and a scientist, which the latter wins by pushing a cooler onto the headcrab. He then does a little dance to celebrate his victory, followed by another headcrab jumping onto his head and killing him. The room then dims to red and a glass object breaking.

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

Notes and references
Kopfkrabbe