Stage in a butterfly's development (5)
I believe the answer is:
larva
'stage in a butterfly's development' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for larva that I've seen before include "Grub, caterpillar stage" , "Woodworm" , "a developmental stage" , "Worm-like insect before metamorphosis" , "Immature form of caterpillar" .)