Pest in a nest (6)
I believe the answer is:
hornet
'pest in a nest' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for hornet that I've seen before include "Run through" , "Large social wasp with fierce sting" , "Small flier" , "A large wasp with serious sting" , "Vespa" .)