It's tricky to demean a worm (8)
I believe the answer is:
nematode
'a worm' is the definition.
(nematode is a kind of worm)
'it's tricky to demean' is the wordplay.
'it's tricky' indicates an anagram.
'to'+'demean'='todemean'
'todemean' is an anagram of 'NEMATODE'.
(Other definitions for nematode that I've seen before include "Long thin worm such as threadworm" , "Type of worm" , "sort of animal" .)