Little is known about the Ants, being most likely a creation of the Book of Eibon similar to the Worms seen within the series. These ants appears far larger and monstrous in appearance then their other counterparts, towering both Noah and even the Kishin in size. Comments from the Table of Contents hints these creations can be created infinitely.
Not much was shown from the ants offensively, though from what is witnessed from Noah fusing with the ants, they're capable of moving at incredible speeds with enough physical power to push their enemies as powerful as Asura as well as withstand even attacks from Asura's Scarves with their thick sin. It's possible, however, that the feats displayed could be due to the effect of "BREW".