Insect lost without a copper (6)
I believe the answer is:
locust
'insect' is the definition.
(locust is a kind of insect)
'lost without a copper' is the wordplay.
'without' indicates putting letters inside ('without' can be similar in meaning to 'outside').
'a copper' becomes 'cu' (chemical symbol).
'lost' going around 'cu' is 'LOCUST'.
(Other definitions for locust that I've seen before include "A deadly grasshopper seen in plagues" , "beast resulting in destruction" , "Voracious insect, travels in swarms" , "Clouts (anag)" , "Swarming, destructive insect" .)