In the swamp biome the snakes can be found everywhere so try to find a land they can climb most rocks so flat ground is your best bet brace yourself against the rocks on the spots so they can't sneak behind you and you can get a clear shot
The dossier says:
"Found only in the dark caves of the island"
They are already wrong! It should say something more like:
"Found everywhere but the dark caves of the island, this creature will gladly ruin your day by jumping out and killing you as soon as you even think about going to the swamp. Nearly impossible to tame because it has to be tamed via passive which is very difficult to do. Worst of all you need to feed them fertilized eggs. Why can't it e a little easier? Up-vote of you agree!