The housefly is proven to be harmful because it carries germs and parasites. However, Bukhari and Abu Huraira thought that one of its wings is curative.
Narrated Abu Huraira:
Allah’s Messenger (ﷺ) said, “If a fly falls in the vessel of any of you, let him dip all of it (into the vessel) and then throw it away, for in one of its wings there is a disease and in the other there is healing (antidote for it) i e. the treatment for that disease.”
Sahih al-Bukhari 5782
Vol. 7, Book 71, Hadith 673