Killing Ants And Its Penance
There are two things in the ethical circle that are to be kept in mind while dealing with animals: 1) There should be a genuine reason to kill them e.g. to save oneself from their harm or saving from an infection epidemic or to obtain meat from them etc. 2) They should be killed in way least painful for them. If someone has killed ants just for the sake of fun, one should repent sincerely and avoid repetition of such an act. If one chooses, one can opt to impose some sort of penalty on oneself e.g. paying a certain amount in the way of Allah or observing a nafal fast etc. However, nothing explicit has been prescribed by Sharia in this regard. For comments of Ghamidi Sahab , please refer to the video below from 9:13 to 10:55 https://youtu.be/Na5nFf0rcCs?t=553