Headcrab

Headcrab
Half-Life character
A headcrab, as seen in Half-Life on the left and its depiction in Half-Life 2 on the right.
First game	Half-Life (1998)

A headcrab is a fictional alien parasitoid found in the Half-Life video game series created by Valve Software. They are the most common and arguably the most iconic aliens in the series.

Headcrabs are depicted as parasitic lifeforms roughly 2 feet (0.61 m) long. 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. Their pair of large frontal claws are for attacking, and as additional support when standing still. Under the headcrab's body is a large rounded mouth surrounded by mangled, rigid flesh with a sharp claw-like beak.

Physically, headcrabs are frail, a few bullets or a single strike from the player's melee weapon being sufficient to dispatch them. They are also relatively slow-moving and their attacks inflict very little damage. However, they can leap surprising distances and heights. Headcrabs seek out larger human hosts, which are converted into zombie-like mutants that attack any living thing they can find. The converted humans are far more resilient than an ordinary human would be and inherit the headcrab's resilience toward toxic and radioactive materials. Headcrabs and headcrab zombies die slowly when they catch fire. The games also establish that while headcrabs are parasites that prey on humans, they are also the prey of the creatures of their homeworld. Bullsquids, Vortigaunts, barnacles and antlions will all eat headcrabs and Vortigaunts can be seen cooking them on several occasions.

While the original Half-Life only has one type of headcrab, Half-Life 2 introduces two major variations, the fast headcrabs and poison headcrabs. Headcrab zombies also receive these variations in Half-Life 2.

The fast headcrab is a faster, more spider-like version of the ordinary headcrab. Its skin is slightly lighter, and it has long, spider-like legs that allow it to move much faster and climb on walls (first demonstrated in Half-Life 2 in Ravenholm). It does not have a beak like the other varieties, instead using the sharp talons at the ends of its legs to latch to hosts. The zombies it creates are stripped of most of their flesh and muscle. When a fast headcrab is shot off the zombie itself it will reveal a completely bare skull with no tissue, which suggests that the fast headcrab completely takes over control of the host's muscles and nervous system and furthermore becomes the potential brain for the host/zombie. The resulting zombies are, like the headcrab itself, much faster than ordinary zombies. It also makes the same shriek that their standard cousins make.