Like Garameddon, Antguirus is a bug and has a lot of characteristics of a beetle. He has a brown head with large antlers of the same color protruding from it. He also has a large brown body and abdomen covered with orange patterning. Another characteristic is his large strong arms ending with strange claw-like hands. Finally, all of that is held up by his short, thin, back legs.
Antguirus was the second monster to battle Greenman. Antguirus was originally a Minion of Maoh which was placed inside a large ant, that latched on to a child's leg. The other children called for Greenman with the Green Calls and Greenman arrived to pry the ant off. After throwing the ant, it further mutated into Antguirus's main form. From there, Antguirus was quickly beaten to the ground, but was turned giant by Tonchiki. Greenman also grew and the two fought. Greenman was badly injured by Antguirus's scalding liquid, but the monster was eventually defeated.
In Go! Greenman, Antguirus is able to expel a black liquid from his mouth.