Its body greatly resembles the Groaner. It is hairless and has dull, rotting brown skin. Compared to the Groaner, the Wormhead has gained much more mass, lacking the visible bones and overall emaciated appearance. The most distinct difference between the Wormhead and its Fog World counterpart is that its head is completely covered with worms.
Wormheads are essentially upgraded versions of the Groaners. Due to Silent Hill's corruptible force, the Groaner transforms into a more grotesque and powerful creature. They have the same abilities and weaknesses as the Groaners: they are very fast and sensitive to sounds, such as Harry's footsteps or a gunshot, and they seem to be just as easy to avoid as the Groaner.
They share the same symbolism as the Groaner, being Alessa's fear of dogs, as well as the Night Flutter's symbolism of Alessa's aversion toward worms, snakes, and the like.
The Wormhead could also prove symbolic of Harry's belief that he may be losing grasp on his sanity, and could also stand for the overall deterioration of all things he had originally known as orthodox. Worms are common decomposers, and seeing a mass of the creatures completing shrouding sight of a dog's head could be a metaphor for one's sanity being eaten away.