Insect in living nature (4)
I believe the answer is:
gnat
'insect' is the definition.
(gnat is a kind of insect)
'in living nature' is the wordplay.
'in' indicates the answer is hidden within the clue.
'GNAT' is hidden within 'living nature'.
(Other definitions for gnat that I've seen before include "Two-winged fly" , "Small fly that bites" , "Tiny thing" , "mozzie" , "Woodland area" .)