Arikimedes - A queen ant monster. Able to release a red acid that could easily melt humans and metal and used used traps during battle. Its personal emblem, worn by the soldiers under his command, was an ant. Hayato Ichimonji and Kazuya Taki attacked the outpost commanded by Arikimedes and stole an egg from there. Trying to recover it, they fought again. Destroyed after getting hit by Kamen Rider #2's Rider Kick and falling into a pond of formic acid.
Arikimedes made a brief return appearance in the monster army of the Kamen Rider vs. Shocker movie, but did not actually have an active participation there.