Set out to catch regular fly (6)
I believe the answer is:
tsetse
'fly' is the definition.
(tsetse is a kind of fly)
'set out to catch regular' is the wordplay.
'out' indicates an anagram (out can mean wrong or inaccurate).
'to catch' is an insertion indicator.
'regular' becomes 'set' (set can mean regular or fixed).
'set' anagrammed gives 'tse'.
'tse' going around 'set' is 'TSETSE'.
(Other definitions for tsetse that I've seen before include "African transmitter" , "source of sleeping sickness" , "carrier of disease" , "bloodsucker" , "Bloodsucking African fly" .)