Burrowing creature ruins the marrow (9)
I believe the answer is:
'burrowing creature' is the definition.
(I've seen this before)
'ruins the marrow' is the wordplay.
'ruins' indicates anagramming the letters.
'themarrow' is an anagram of 'EARTHWORM'.
(Other definitions for earthworm that I've seen before include "Soil dweller" , "that's throwing up on the lawn" , "Tunneller" , "Garden burrower" , "One burrows" .)