Desert creature (3)
I believe the answer is:
rat
This clue is a double definition.
'desert' is the first definition.
(abandon treacherously)
'creature' is the second definition.
(rat is a kind of animal)
(Other definitions for rat that I've seen before include "Scumbag" , "Tell-tale" , "Betrayer" , "Strike-breaker" , "Grass" .)