Headcrabs are small creatures, roughly the size of a pumpkin.
They are covered in smooth skin, which varies in color between subspecies, and crawl on four short legs. These legs provide enough jumping power to leap up to 3 meters (10 feet) in any direction.
Their underbelly is almost completely covered by a large, jawless mouth, with a hidden "beak" used for feeding and for latching onto the skulls of victims.
Normal Headcrab Edit
The Headcrab can appear harmless at a glance: it is small and slow-moving with its tiptoe-like gait. Although it can quickly leap long distances using its hind legs, tilting its body upwards to turn its mouth towards its target, such an assault can only inflict minor injuries with the claws, legs and teeth.
However, the Headcrab's main goal is not to kill, but to attach itself onto an appropriate host's head.
Using its leaping ability, it can reach a host's head and attempt to burrow its beak through the skull. Once successful, the Headcrab takes control of the host's nervous system and causes physical alterations to the host's body, such as causing its fingers to grow into claws, via an unknown biological process.
The host then rips open its own torso, revealing the stomach and other organs, for feeding purposes. Such a Headcrab-controlled host is called a Standard Zombie (distinct from Zombies created by other Headcrab subspecies, which have different characteristics).
Fast Headcrab Edit
The Fast Headcrab looks much slimmer and more agile than a normal Headcrab, having thinner, spindly legs, smoother, lighter bodies and no visible mouth-parts. Fast Headcrabs share many of the vocalisations of the standard Headcrab.
Examined up close, Fast Headcrabs have wart-like bumps on their skin. The legs of a Fast Headcrab also have elongated claws, which serve as weapons as well as a means to latch on to surfaces, where they then wait to attack unsuspecting prey. The victims will turn into fast zombies.
The Fast Headcrab attacks in much the same way as a normal Headcrab, and does about the same amount of damage. The main difference is that Fast Headcrabs close distance between themselves and their target very quickly before proceeding to leap at the target frantically. Their speed and unpredictable movement patterns make them difficult targets, and they can be very dangerous in groups of three or more.
Poison Headcrab Edit
At a walking pace, the Poison Headcrab is the slowest of Headcrabs, but panics and runs away if attacked or set on fire. Poison Headcrabs move slowly and cautiously when maneuvering, but leap with incredible speed while releasing an angry squeal when a suitable host is in a clear line of sight. As an ambush tactic, it leaps at and poisons a viable host in an attempt to create a Poison Zombie. Poison Headcrabs make a sound similar toRattlesnake before launching an attack. Also, when idle, the Poison Headcrab can be heard making mouse-like chirping sounds, possibly in an attempt to lure prey to its location.
Poison Headcrabs are arguably the most intelligent of their species as they can dodge/react to enemy fire and do not always aggressively attack enemies head-on in a reckless manner.
Headcrab Canister Edit
Headcrab Shells are a form of biological weaponry used by theCombine. These shells are launched over long distances and land in enemy-controlled territory, releasing a payload of Headcrabs. Used primarily to flush out and destroy Resistance bases, they are responsible for the destruction of many communities. The shells themselves seem to be a type of mortar or artillery, packing an explosive charge as they land. As such, empty shells are also seen being used as conventional artillery by the Combine to destroy entrenched positions or buildings. They are very deadly and should be avoided!