Mercy Killing?

Mum used to be very careful about killing pests, no matter how troublesome they can be.  Being a practising Buddhist, she tries to avoid unnecessary killing. If she finds ants crawling around food, she will gently pull them away and if they should be killed in the process, she will say to them, "May you all be reborn as human beings".  How many of us can do this, I wonder. Most of the time, we just kill pests without a thought, and certainly without worrying about their next birth!