Wrathful, that is, about the vermin (5)
I believe the answer is:
irate
'wrathful' is the definition.
(synonyms)
'that is about the vermin' is the wordplay.
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'about' is an insertion indicator.
'the vermin' becomes 'rat' (I've seen this in other clues).
'ie' going around 'rat' is 'IRATE'.
(Other definitions for irate that I've seen before include "Boiling" , "I tear away, being annoyed" , "Fuming" , "Livid" , "Not happy" .)