I'd suggest checking out the C-Virus page on the RE Wikia, as the virus articles are pretty detailed. Here's an excerpt that more directly references what you're asking about, though:
Overall, the C-Virus combines the traits and abilities of the two viruses it was derived from, possessing the adaptive mutations of the G-virus and the combustible properties of the T-Veronica virus. The T-Veronica virus is visible in some of the mutations where the mutations usually result in the development of insect-like appendages.
The t-Virus can only properly function by consuming the cell in order to produce its energy. This slow breakdown of cells leads to the gradual breakdown of the host, causing necrosis. The virus incorporates itself into the host's DNA, which substantially alters it. This is why creatures, such as bees and spiders, only have very minor mutation, such as increased size, when compared to the human mutation caused by the virus.
Within the time frame of an hour, the decayed skeletal and muscular system is reconstructed into a stronger and more durable form. Development can be seen of sharp canine teeth and razor claws, fresh blood seeps into remaining skin giving it a reddish hue, advances in decomposition, and intact eyes become a bright white. Umbrella researchers at the Arklay Laboratory have dubbed this stage "V-ACT", referring to the resulting creature also known as a "Crimson Head". To awaken, the brain must be jolted back to consciousness with a slight but important increase in intelligence, and large increase in agility and aggressiveness.
The form the T-Virus takes on depends on the physical state of the host, whether they be living, near dying or dead, and whether they're a human or an animal/insect. The C-Virus uses the T-Veronica virus as a base, so the insect and animal related atributes present in the T-Virus are also found in the C-Virus.