Primates hate serpents. Probably because when they stick their little hands into a bird nest for eggs they could find the snake that had gotten there first.
OK, we can go with that if you like, there could be some primal instinct. But there are so called pagan cultures all over the world who have no fear of serpents, yet just about everyone with Christian roots has an ingrained deathly fear of all snakes. But my curiosity is with the early Christian hatred for snails, what’s that all about? :)