The garter snake is a small-to-medium sized snake that is common all over North America. They want to eat toxic newts. They have to be extra-toxic, carrying that metabolic load, just to maybe make the garter snakes think twice about eating them. One paper found odd little pockets of unexpectedly toxic newts up there. But so far, the snakes and newts don’t seem to have started an arms race like they have on the mainland.