Little biter (4)
I believe the answer is:
gnat
'little biter' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for gnat that I've seen before include "Insect like small mosquito" , "Two-winged fly" , "Small bloodsucker" , "a little bit of a nuisance" , "Small (swarming) fly" .)