

The Gonarch is a massive, heavily armored version of a headcrab that appears only once as a boss fight towards the end of Half-Life in Xen. Headcrab zombies also receive these variations in Half-Life 2. While the original Half-Life only contains one type of headcrab, Half-Life 2 introduced two major variations: fast headcrabs and poison headcrabs. Bullsquids, Vortigaunts, barnacles and antlions will all eat headcrabs and Vortigaunts can be seen cooking them in several locations in-game. The games also establish that while headcrabs are parasites that prey on humans, they are also the prey of the creatures of their homeworld. Headcrabs and headcrab zombies die slowly when they catch fire.

The converted humans are more resilient than an ordinary human would be and inherit the headcrab's resilience toward toxic and radioactive materials. Headcrabs seek out larger human hosts, which are converted into zombie-like mutants that attack any living lifeform nearby. However, they can leap long distances and heights. They are also relatively slow-moving and their attacks inflict very little damage. Physically, headcrabs are frail: a few bullets or a single strike from the player's melee weapon being sufficient to dispatch them. Under the headcrab's body is a large rounded mouth surrounded by mangled, rigid flesh with a sharp claw-like beak. Their pair of large frontal claws are for attacking, and as additional support when standing still. The common headcrab variant has rounded bodies with four legs for movement, two of which are long clawed legs at the front and two stubby legs at the back. The game is set during May 200- in a remote area of New Mexico, USA at the Black Mesa Research Facility a fictional complex that bears many similarities to both the Los Alamos National Laboratory and Area 51.Headcrabs are depicted as parasitic lifeforms roughly 2 feet (0.61 m) long. After an experiment that goes horribly awry when an unexpected Resonance Cascade (an apparently completely fictitious occurrence) rips dimensional seams that devastate the facility, Gordon must fight to escape the now alien-infested facility as creatures from another world - known as Xen - subsequently enter in ever-increasing numbers through these dimensional seams. Gordon Freeman, a recent MIT graduate in theoretical physics, and also a recent employee at Black Mesa. N Half-Life, players assume the role of the protagonist, Dr. Designed for Microsoft Windows, the game uses a heavily modified version of the Quake engine, called GoldSrc.

The player takes the perspective of scientist Gordon Freeman. Half-Life, stylized as HλLF-LIFE, is a science fiction first-person shooter developed and published by Valve.
