It requires the removal of some vermin, usually (5)
I believe the answer is:
'it requires the removal' is the definition.
The definition suggests a singular noun but the answer is not.
'some vermin usually' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'MINUS' is hidden within 'vermin usually'.
'of' acts as a link.
Can you help me to learn more?
(Other definitions for minus that I've seen before include "Take-away (sign)" , "Negative arithmetic operation" , "'Take away' sign" , "(Of temperature) below zero" , "Lacking; below zero" .)