Scoundrel entering spies insect (6)
I believe the answer is:
cicada
'insect' is the definition.
(cicada is a kind of insect)
'scoundrel entering spies' is the wordplay.
'scoundrel' becomes 'cad' (cad is a kind of scoundrel).
'entering' means one lot of letters goes inside another.
'spies' becomes 'CIA' (Central Intelligence Agency).
'cad' inserted inside 'cia' is 'CICADA'.
(Other definitions for cicada that I've seen before include "Droning insect" , "Noisy winged insect" , "Bug sounding at night" , "Stridulating insect" , "The insect produces a high-pitched sound" .)