The giant maggot were similar to regular maggots except for their immense size, sharp fangs and thick skin. They were invulnerable to bullets but armour piercing bullets, flame-throwers and fire bombs could defeat them. They would eventually develop into giant flies.
The giant maggots were created by the chemicals dumped by BOSS' Global Chemicals. The giant maggots killed anyone who came near them, due to their aggressive nature and the deadly chemicals. It was eventually discovered by Professor Cliff Jones that his edible fungus was poisonous to the maggots and it was used to wipe out the entire species.