Files about insects (5)
I believe the answer is:
flies
'insects' is the definition.
(fly is a kind of insect)
'files about' is the wordplay.
'about' indicates an anagram.
'files' is an anagram of 'FLIES'.
(Other definitions for flies that I've seen before include "Trouser zip area -- travels through the air" , "Insects; goes quickly" , "Insects; passes swiftly" .)