Bloodsucking parasitic insect (5)
I believe the answer is:
louse
'bloodsucking parasitic insect' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for louse that I've seen before include "Wingless bloodsucker" , "Human parasite" , "25 [PARASITE]" , "Rogue" , "Common parasite on animals" .)