Bug spies taking on bad guy (6)
I believe the answer is:
cicada
'bug' is the definition.
(cicada is a type of insect)
'spies taking on bad guy' is the wordplay.
'spies' becomes 'CIA' (Central Intelligence Agency).
'taking on' indicates putting letters inside.
'bad guy' becomes 'cad' (I've seen this in another clue).
'cia' enclosing 'cad' is 'CICADA'.
(Other definitions for cicada that I've seen before include "Droning insect" , "six-footer?" , "Flier" , "Large chirping insect" , "Chirpy type" .)