Larva of the Papilio xuthus butterfly. A larva (/ ˈ l ɑːr v ə /; pl.: larvae / ˈ l ɑːr v iː /) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase of their life cycle.. A larva's appearance is generally very different ...