Colonial soldier's surprised reaction interrupting a tirade? (4,3)
I believe the answer is:
army ant
'colonial soldier's' is the definition.
(soldier is a type of ant)
'surprised reaction interrupting a tirade?' is the wordplay.
'surprised reaction' becomes 'my' ('my!' can be an expression of surprise).
'interrupting' indicates putting letters inside.
'tirade?' becomes 'rant' (both can mean an angry outburst).
'a'+'rant'='arant'
'my' put within 'arant' is 'ARMY ANT'.
(Other definitions for army ant that I've seen before include "Stinging insect" , "Group-foraging insect" , "tropical insect" , "Foraging insect" , "Soldier, perhaps" .)