Peeress offers to protect last of tiger beetles (9)
I believe the answer is:
ladybirds
'beetles' is the definition.
(ladybird is a kind of beetle)
'peeress offers to protect last of tiger' is the wordplay.
'peeress' becomes 'lady' ('lady' can be a synonym of 'peeress').
'offers' becomes 'bids' (bid is a kind of offer).
'to protect' means one lot of letters goes inside another.
'last of' suggests the final letters.
The final letter of 'tiger' is 'r'.
'bids' placed around 'r' is 'birds'.
'lady'+'birds'='LADYBIRDS'
(Another definition for ladybirds that I've seen is " Spotted beetles that feed on aphids".)