Fly larva (6)
I believe the answer is:
maggot
'fly larva' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for maggot that I've seen before include "Larva feeding on decaying matter" , "one that may be in decay" , "Fly larva" , "Larva of housefly or bluebottle" , "Blowfly larva" .)