Giant maggot

Biology
A massive Maggot that are similar to regular Maggots except it's skin is invunrable to bullets, but armour piercing bullets, flame-throwers and fire bombs can defeat them.

Life Cycle
Normal Maggots until infected by the waste from Global Chemicals, they then grow enormous, and recive chitin plates (Bulletproof) but they then evolve into a Larval Stage which evolves into the Giant Fly that UNIT had to shoot down with a Tank.

Technology
None, unless you count BOSS controlling them and Justin Stevens

History
Created by the chemical's dumped by BOSS's Global Chemical's, The Giant Maggot's kill any who comes near them but it's Professor Cliff Jones who discovers that his edible fungus that he and his group are creating is posionous to the Maggots and it wipes out the entire species before BOSS is able to mobilse and evolve the Maggots.