Flies alone (5)
I believe the answer is:
solos
'flies alone' is the definition.
('solo' can be a synonym of 'fly alone')
This is all the clue.
(Other definitions for solos that I've seen before include "Passages for one player" , "Pieces of music for one voice or instrument" , "Numbers" , "Unaccompanied parts" , "Musical passages for one instrument" .)