Wurms can reach up to three metres long, and thirty to forty centimetres in diameter. Their skin is thick and tough, with a brown, black and dark yellow mottled colouration, which acts as camouflage in the dark tunnels.
They have short, sharp spines sticking up from their backs, which have no apparent purpose, as they cannot be used for attack, defence or display.
They have a strange, fleshy head that consists of three 'petals' which close together as a mouth. At the centre of these three petals is a fleshy circle, armed with rows of sharp teeth. The circle can close around itself to push food down the oesophagus.
Wurms are burrowers, and ambush predators. They live solitary lives, and can produce eggs alone, which they lay and then abandon. They are often laid in other creatures' nests.
Their traditional hunting method is to burrow through soil until they are just by a wall of one of the tunnels in the catacombs. When something comes past, they launch themselves forward, breaking through the thin layer of soil and smashing straight into their prey.
Wurms have a varied diet. They prefer meat, but can also feed on soil itself when they need to.