Mum with little hesitation leaving insect (4)
I believe the answer is:
moth
'insect' is the definition.
(moth is a kind of insect)
'mum with little hesitation' is the wordplay.
'mum with' becomes 'mot' (I can't explain this - if you can you should believe this answer much more).
'little' suggests taking the first letters.
The initial letter of 'hesitation' is 'h'.
'mot'+'h'='MOTH'
'leaving' acts as a link.
Can you help me to learn more?
(Other definitions for moth that I've seen before include "Night-flying insect" , "Night flier" , "Lepidopteran" , "night flyer" , "Night flying insect" .)