Fly back out of Katanga (4)
I believe the answer is:
gnat
'fly' is the definition.
(I've seen this before)
'back out of katanga' is the wordplay.
'back' says the letters should be written in reverse.
'out of' indicates the answer is hidden within the clue.
'tang' is hidden within 'katanga'.
'tang' written backwards gives 'GNAT'.
(Other definitions for gnat that I've seen before include "mozzie" , "Woodland area" , "a little bit of a nuisance" , "Any of various small biting flies" , "Two-winged fly" .)