There are several methods to kill wasps instantly. One common method is to use an insecticide designed explicitly for wasps. You can also try using a spray made with vinegar or lemon juice as these substances can be irritating to wasps. If you don't have any insecticide, you can try using a fly swatter or even your hands to kill the wasp. However, it's important to exercise caution when dealing with wasps, as they can sting if they feel threatened.