Board Thread:General Discussions/@comment-1030114-20131208093935/@comment-25285745-20140903192124

Shockirus are parasites. Hayashida even says "I think it was a parasite, feeding on Godzilla" in the Japanese version of the movie. Shockirus is a louse, lice are parasites, so logically Shockirus is a parasite that feeds on Godzilla. While M.U.T.O. is a life-threatening parasite that seems to lay eggs in its hosts, Shockirus probably didn't affect Godzilla very much due to its size.