Is it forbidden to hunt flies by hitting them with wood due to the harm it causes them?

The Sharia permits killing flies because they are harmful and a primary cause of disease transmission, as a means of warding off harm. This is indicated by the Prophet Muhammad's (peace be upon him) saying: "If a fly falls into the drink of any one of you, he should immerse it completely and then remove it, for in one of its wings there is a disease and in the other there is a cure" (narrated by Al-Bukhari). This provides evidence for the permissibility of killing them, and "immersion is more effective in killing than mere striking."