The Larva, also known as the Insectus, is an enemy from Final Fantasy IV. It is not that difficult to defeat, despite usually appearing with other Larvae and Eyewing Moths. Cecil and Kain will have no problem dealing with these beasts early on in the game, but things might get a bit more difficult as soon as Cecil has to start looking out for Rydia. Still, the best way to finish the Larvae off is with a couple physical attacks.
In the DS version, Larvae can cast Slow. In the PSP version, it counters Osmose when attacked (but not killed) with magic.