Fly larva (6)
I believe the answer is:
maggot
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">fly larva</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(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" .)