Character from Half-Life 2 by Valve
Xen's most successful parasite — small, tenacious, and responsible for more nightmares than the entire Combine army.
Headcrabs are simple creatures with a simple lifecycle: find a head, attach to it, take control. The host doesn't die — it's rearranged. The torso splits open, the arms elongate, and the resulting zombie shambles forward making sounds that might be screaming. If you listen to zombie vocalizations played in reverse, you can hear the host begging for help. The Combine recognized their military potential and industrialized them. Headcrab shells — artillery canisters packed with live headcrabs — are launched into populated areas to create zombie infestations. Ravenholm was destroyed this way. It's biological warfare using alien fauna, and it's the Combine's most cost-effective terror weapon. For the player, headcrabs are Half-Life's signature horror element. The skittering in dark vents. The distant shriek of a fast zombie. The wet thud of something landing on a surface just behind you.
Roughly the size of a large cat, with a bulbous, skin-colored body and four hooked legs. A sharp beak on the underside latches onto a host's head. They move in scuttling bursts, leaping impressive distances to attack. Variants include fast headcrabs (long-legged, skeletal, and terrifyingly quick), poison headcrabs (dark-bodied, glossy, with neurotoxic venom), and standard headcrabs. The Combine weaponizes them — headcrab shells (canisters) are lobbed into resistance positions to create instant zombie outbreaks.
Also known as: Headcrabs, Crabs, Headhumpers