Fish coming back for fly (4)
I believe the answer is:
gnat
This clue might be a double definition.
'fish coming back' is the first definition.
The definition and answer can be both animals as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'for fly' is the second definition.
(type of insect)
Can you help me to learn more?
(Other definitions for gnat that I've seen before include "Stinging insect" , "Small (swarming) fly" , "Small biter" , "Tang (anag.)" , "Something that bites" .)