During the Raccoon City Destruction Incident, many creatures were heavily mutated by the spreading T-Virus. The Giga Bite was an ordinary flea that grew to tremendous size upon infection. The virus also triggered a substantial change in behaviour: the creature's offspring - mutated fleas referred to as "Mega Bites" - would exhibit behaviour more similar to ants, acting as a social hierarchy with the Giga Bite as the queen.
A group of Raccoon City survivors attempted to pass through the ruined South Raccoon Street subway station where the Giga Bite and its offspring had made their home. The Giga Bite would remain in place, protected by several Mega Bites, and would attack from a distance by rolling its offspring like bowling balls across the tracks towards the survivors. Due to its considerable bulk, the Giga Bite could not move and proved to be an easy target for the survivors who destroyed it with assault weaponry and Molotov cocktails.