Leaf-chewing creature (4)
I believe the answer is:
flea
'creature' is the definition.
(flea is a kind of creature)
'leaf-chewing' is the wordplay.
'chewing' indicates anagramming the letters.
'leaf' anagrammed gives 'FLEA'.
(Other definitions for flea that I've seen before include "Blood-sucking parasites" , "irritant type" , "Bug" , "Jumping bloodsucker" , "source of infestation" .)