We hear innocent creature speak well of parasitic suckers (8)

'parasitic suckers' is the definition.

'we hear innocent creature speak well' is the wordplay.
'we hear' indicates a 'sounds like' (homophone) clue.
'innocent creature' becomes 'lamb'.
'speak well' becomes 'preys' (I can't explain this - if you can you should give a lot more credence to this answer).
'lamb' is a homophone of 'lam'.
'lam'+'preys'='LAMPREYS'

'of' acts as a link.