Insect occupying dung naturally (4)
I believe the answer is:
gnat
'insect' is the definition.
(gnat is a kind of insect)
'occupying dung naturally' is the wordplay.
'occupying' says the answer is hidden in the clue (letters for the answer occupy part of the clue).
'GNAT' is hidden in the letters of 'dung naturally'.
(Other definitions for gnat that I've seen before include "Biting pest" , "Tiny biter" , "little irritation" , "Something with bite" , "Small biter" .)