But they don't hurt the angler (5)
I believe the answer is:
bites
'but they don't' is the definition.
The definition suggests an adverb but the answer is not.
'hurt the angler' is the wordplay.
'hurt' becomes 'bite' (bite is a kind of hurt).
'the angler' becomes 's' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'bite'+'s'='BITES'
Can you help me to learn more?
(Other definitions for bites that I've seen before include "Morsels" , "Tears with the teeth" , "Mouthfuls" , "Breaks with the teeth" , "Stings" .)