I'm a spy ranting about bug (7,6)
I believe the answer is:
praying mantis
'bug' is the definition.
(I know that praying mantis is a type of mantid)
'i'm a spy ranting about' is the wordplay.
'about' is an anagram indicator.
'im'+'a'+'spy'+'ranting'='imaspyranting'
'imaspyranting' is an anagram of 'PRAYING MANTIS'.
(Other definitions for praying mantis that I've seen before include "Large carnivorous insect" , "Rags in my paint (anag) -insect" , "Small creature" , "Pagan ministry (anag.)" , "Carnivorous insect resembling a grasshopper" .)