Mutation and BehaviourEdit
Once a Headcrab successfully attaches to a host, the Headcrab's alien physiology causes various "mutations" to manifest in its host, such as increased strength and a "maw" that appears to be a ripped open chest cavity with no visible sternum, as well as elongated fingers/claws. Occasionally, Headcrab zombies may survive losing both legs and their lower torso, and continue to crawl along using their arms. In most cases, a Headcrab remains attached to its host until the zombie is destroyed, although they will occasionally detach from the host if it is rendered immobile by its injuries, some horrified sounds emanating from zombies imply that, while severely injured, the host is at least partially aware of its horrific situation.Certain Zombies can be found "sleeping" and stand up to attack enemies if they get too close or are attacked.
Due to the large amount of humanoid species there are many variants of Headcrab Zombies seen throughout the universe however here are a few variants:
Standard Zombies: The main variant of Headcrab Zombies, these creatures are the most common due to the large amount of human civilian areas. These creatures are fairly weak and slow, plus they are easy to kill. They use a standard zombie claw attack but it is harmless to those who know self-defence techniques or are wearing armor. Their appearence varies depending on the clothing they are wearing but they have the standerd features most zombies have.
Spartan Zombies: Spartan Zombies are the result of a headcrab latching onto the head of a UNSC soldier in spartan armor. The spartan zombie variation is slow like the standard zombie, however they may pull out a sticky bomb and attempt to do a kamikazi attack. Their appearence is that of a spartan however their appearence varies from the armor color and modifications plus the 'maw' is not visible, however they have the red claws like most standard zombies.
Borg Zombies: Also known as 'zomborgs' by some members of hellcat squadron, borg zombies run rather then march slowly then other zombies. Borg Zombies have been proven difficult to kill due to the fact they still use the adaptive shielding and they may occasionally use the plasma weapon on their prosthetic arm. Upon death, borg zombies may 'fall apart' in which the cybernetic limbs of the host body will spotaniosly dismember automaticaly. Their appearence is that of a normal borg drone however the headcrab is attached to its head, and in the claws of the zombie are grey instead of red, and they do not have the 'maw' on their stomach due to the exoplating.
8472 Zombies: A rarely seen variant of headcrab zombies, the species 8472 zombies are the result of a headcrab merging with a severely injured member of species 8472. These creatures run faster then the previous variants however they are extremely fragile and upon death they explode and release an acidic compound. The appearence of the 8472 zombie is much more hellish looking and they look extremely malnourished with dark green skin.
Tiberium Zombies: Headcrabs have been proven to be immune to the effects of Tiberium, however that doesn't mean that their host is immune. Tiberium Zombies are the result of a Headcrabs host being exposed to liquid, crystal, or vapor tiberium. These zombies are dangerous due to the high amount of tiberium in their body, it is recommeneded that they be killed from a distance due to the fact upon death their body does the equivilant of a nano nuclear bomb, that can irradiate a small area around them. Tiberium Zombies vary from looks however their claws are black with a small amount of a green color, and their maw is said to expose organs that have been faced the malicious side affects of tiberiums due to this fact their organs are black. Another unconfirmed report about Tiberium Zombies is that they are bioluminescent in dark ares, however this has yet to have been determined.
Although very robust paracites, they have a few weaknesses: the Flood, a similar parasitic species, is very much immune to the Headcrabs, as are 'partners' of Flood Separatist Augmentation Forms. One very potent weakness, however, is supernatural power. The Headcrabs cannot infect anyone with any form of supernatural ability, no matter how inert.