RichThesaurus
like a blue-arsed fly
vs
posthaste
like a blue-arsed fly
adj
To be frantic, harried or restless
posthaste
adv
quickly, as fast as someone travelling post; with great speed
How often have the words
like a blue-arsed fly
and
posthaste
occurred in a corpus of books?
(source:
Google Ngram Viewer
)