I would say they are not closely related and we are seeing convergent evolution... Pretty much every area has it's own type of snake or two to fill the semi aquatic niche. While many of them are very different, they all seem to share similar habits, especially the habit of wanting to spontaneously grab anything that flops about like a fish! The only snakes I know that do that are these types. A lot of times the only way I can convince a stubborn water snake to eat a pinky is by flopping it with my tongs while it's wet. Works like a charm! Same with my liophis! I would imagine any species that prefers the semi aquatic lifestyle learned to do this because when there is a fish or tadpole flopping in the shallows, it's either grab it quickly or it's gone!!! The only thing it would do to any of my rat snakes, kings, milks, or other typical colubrids would be to royally tick them off and get their tails rattling! But much like semi aquatic snakes and chasing after things that flop, most all of my rat snakes and misc colubrids, from the new world and the old, shake their tails with anger and excitement. And then there is my chondro who uses her tail as a caudal lure, just the same as the copperhead does!