The Plaga is the only existing parasite able to cause mutagenic reactions upon the host, allowing the host to mutate horrifically. As the parasite is based in the chest and controls all, the removal of the host's head can do nothing but make things worse. In areas of low UV radiation-night time for instance-Las Plagas would be able to use parts of its body as a weapon.
If needed, some subspecies are able to escape and live for a short period of time without a host. Type 2 and Type 3 Plagas were genetically created through experiments by Tricell, include improvements over the original such as making parasite maturation occur in a matter of seconds, and improving strength and agility in the infected, respectively.
It is unclear what is the relation, if any, this parasite has to the NE-α Type, although both types of host show similar symptoms of infestation.
It seems that in Resident Evil: Damnation there is a new variation similar to Type 2 Plagas but the details are unknown about the genetics of the strain seen in the movie. This strain of Plaga is contagious but is affected by the dominant strain plaga like the original strain. The infected are referred as Ganados like in Resident Evil 4.
The NE-α Type was biologically engineered by Umbrella, and was the European answer to the perfection of the ultimate B.O.W., Tyrant. This parasite was used in the Nemesis Project to stabilize Tyrants, and created the Nemesis-T Type.
The parasite is dangerous however, and Human hosts will generally die within minutes. The only known successful hosts were Lisa Trevor and the Tyrant (T-103 Model)s that would become the basis of Nemesis-T Type.
When an adult "G" implants its embryo within a host whose DNA is incompatible with the carrier, the embryo would live as a parasite in the hosts body rather than bonding with it.
After a relatively short period of gestation, generally between a minute and ten minutes, the Embryo would erupt from the host's chest and begin its life without the need of another host.
After becoming an adult, it produces more G-creatures. However, these third-generation "G" no longer need a host and would be born already prepared for survival.
The NE-β Type was biologically engineered by Umbrella, presumably as an attempted improvement over the NE-α. The strain was discontinued and stored in the B.O.W. programming lab inside the Dead Factory.
Physically, these parasites resemble overgrown, yellow spiders, and they tend to move in fast jerking motions. Their method of bonding with a host is to clamp down with their jaws on the base of the target's neck, possibly utilizing the spinal cord as a conduit. Interestingly, these parasites seem to target only T-Virus infected zombies as their hosts. Upon bonding, the host immediately becomes faster and more resilient, shrugging off damage that would have proven fatal to a non-bonded individual.
The only known sightings of these parasites were the specimens in the B.O.W. programming lab, which bonded to zombies when first encountered by Wolfpack, and later bonded to a Tyrant when encountered by Echo Six.