Mosquito, by nature (5)
I believe the answer is:
biter
'mosquito by nature' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for biter that I've seen before include "Vicious dog perhaps" , "Someone eating" , "One may snap" , "He who may be bit in tribe" , "Tribe (anag.)" .)