Spies take scoundrel to be an insect (6)
I believe the answer is:
cicada
'insect' is the definition.
(cicada is a kind of insect)
'spies take scoundrel' is the wordplay.
'spies' becomes 'CIA' (Central Intelligence Agency).
'take' means one lot of letters goes inside another.
'scoundrel' becomes 'cad' (cad is a kind of scoundrel).
'cia' placed around 'cad' is 'CICADA'.
'to be an' is the link.
(Other definitions for cicada that I've seen before include "jumpy creature" , "Large bug" , "Flier" , "Droning insect" , "Chirpy little thing" .)