Second line not going straight through medical service gives you butterflies (8)
I believe the answer is:
monarchs
'butterflies' is the definition.
(I've seen this in another clue)
'second line not going straight through medical service' is the wordplay.
I cannot quite understand how this works, but
'second' could be 'mo' (both are short periods of time) and 'mo' is found within the answer.
'line' could be 'arch' (arch is a kind of line) and 'arch' is located in the answer.
This explanation may well be incorrect...
'gives you' acts as a link.
Can you help me to learn more?
(Other definitions for monarchs that I've seen before include "Kings, queens etc." , "Hereditary heads of state" , "Hereditary rulers" , "Kings, queens and emperors" , "Kings and royal rulers" .)