Opposed to predatory insect shedding skin (4)
I believe the answer is:
anti
'opposed to' is the definition.
(anti means opposing something)
'predatory insect shedding skin' is the wordplay.
'predatory insect' becomes 'mantis' (I've seen this in another clue).
'shedding skin' means to look at the middle letters (the word's 'skin' is removed).
The middle letters of 'mantis' are 'ANTI'.
(Other definitions for anti that I've seen before include "Prefix meaning against" , "Not favouring" , "on the other side" , "(Person who is) not in favour" , "Adversary" .)