The Gulp Worm was produced by exposing a common earthworm to the T-virus. Its size and strength increased exponentially and its skin became extra-sensitive. It can detect vibrations in the ground and tracks them in order to attack prey on the surface. As its name suggests, it can swallow a human being whole. Research on the Gulp Worm was still in the prototype stage when Rockfort Island was destroyed in an attack led by former Umbrella operative Albert Wesker. Before the attack, the creature was used in training exercises for Umbrella's Anti-B.O.W. militia teams.
Claire Redfield encountered the Gulp Worm while trapped on the besieged Rockfort Island as it dwelled beneath the ground outside the main research area. At this point, the player can choose to confront the beast or avoid it altogether, since killing it offers no special reward. Chris Redfield also encounters the monster when he arrives at Rockfort after the base's destruction. As with Claire, fighting the Worm is optional, but if Chris kills the creature he will obtain a lighter from Rodrigo Paval - who obtained it from Claire and got swallowed by the Worm upon meeting Chris - which in turn will allow him to acquire a pair of Uzi machine pistols. The Gulp Worm has no distinct target areas and can be damaged with any weapon, though shotguns and explosives are the better choices for killing it quickly.