What is the purpose of the pupa stage in the butterfly life cycle?

Grasshoppers do not go through a pupal stage. Insects fall into two major groups, holometabolous (complete metamorphosis: pupal stage) and hemimetabolous (incomplete metamorphosis: no pupal stage). Grasshoppers are hemimetabolous, like crickets, mayflies, stinkbugs, etc., and insects that undergoe incomplete metamorphosis do not have a pupal stage. Holometabolous insects such as flies, butterflies, beetles, wasps, etc. do undergoe complete metamorphosis and they all have a pupal stage.