Bite from climbing insect (4)
I believe the answer is:
tang
'bite' is the definition.
(thesaurus)
'climbing insect' is the wordplay.
'climbing' shows that the letters should be reversed in order (in a down clue, letters climb up).
'insect' becomes 'gnat' (gnat is a kind of insect).
'gnat' reversed gives 'TANG'.
'from' acts as a link.
(Other definitions for tang that I've seen before include "Thrash with good" , "Pungency" , "Sharp flavour" , "Gnat (anag.)" , "tastefulness" .)