Killing mosquitoes

Q: I read in the name of the Arizal that it is forbidden to kill bugs. What is the law?
A: The basic Halachah is that it is permissible to kill mosquitoes that are bothering you, and this applies to mice and other animals as well. The Arizal was strict. Everyone is obligated to follow a law, but a stricture is the personal decision of each person. Ha-Rav Moshe Sternbuch has a Teshuvah on this issue in Shut Teshuvot Ve-Hanhagot (2:726). He was asked: Is it permissible to kill flies? He answers that there is no prohibition of "tza'ar baalei chaim" (cruelty to animal) for such small creatures. He quoted from the Yavetz (Shut Yavetz #110) that the prohibition of "tza'ar baalei chaim" applies to animals who perform labor, and it is doubtful whether it applies to dog and cats. Ha-Rav Sternbuch wrote that he thinks that this prohibition certainly applies to cats and dogs but not to these tiny bugs. It is therefore completely permissible to kill them. He also mentions that the Arizal would not kill any creature and explains that it was not on account of "tza'ar baalei chaim" but rather because of his great holiness that he did not want to destroy any creature for which there was some need in the world. In Shut Igrot Moshe (Choshen Mishpat 2:47), Ha-Rav Moshe Feinstein wrote that if possible it is preferable not to kill the insects, mice, etc. with your bare hands. His proof is that the Torah promises that in the destruction of the "Ir Ha-Nidachat" (the wayward city – see Devarim 13:13-19) that Hashem will instill those who carry it out with mercy. The Or Ha-Chaim (Devarim 13:18) explained there is a need for the promise since by nature when one kills it makes him cruel. It is therefore better not to kill the bugs, mice, etc. with your hands. This, however, is also a stricture and it is also permissible if it is not possible to do it any other way.