Nymphs line a rave dancing? (6)
I believe the answer is:
larvae
'nymphs' is the definition.
(both are immature forms of insects)
'line a rave dancing?' is the wordplay.
'line' becomes 'l'.
'dancing?' is an anagram indicator.
'rave' is an anagram of 'rvae'.
'l'+'a'+'rvae'='LARVAE'
(Other definitions for larvae that I've seen before include "Insects just out of the eggs" , "Immature forms of insects" , "Insects in immature state" , "Insects in the first stage of life" , "Immature forms of invertebrates" .)