butterfly stage (11)
(Other definitions for caterpillar that I've seen before include "Moth/ butterfly larva" , "Heavy tracked earth-moving vehicle" , "sort of grub" , "Tiny creature" , "8 17" .)
'butterfly stage' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for pupa that I've seen before include "Developing butterfly" , "developing creature" , "So peacock may have appeared" , "middle stage" , "Immature insect" .)
(Other definitions for larva that I've seen before include "Immature stage of an insect" , "Early stage of creature" , "Animal in immature state" , "Grub; insect" , "Juvenile form of insect" .)