I hate to add to an already rediculously long list of insane stories that people actually believe, but around here, and I imagine in many other places, there are a couple I can think of right off hand that are so persistant that the majority of "snake knowledgable" people I have spoken with believe them.
First is the belief that cottonmouths will gather into large breeding balls and travel around lakes or down rivers, mobbing and biting anyone they come in contact with. No doubt these people have seen large masses of aquatic snakes that look similar to cottonmouths, and then thanks to movies like Lonesome Dove, add the mobbing and biting part. But of course they are seeing various Nerodia congregating for breeding and feeding. There is an area here in a wildlife refuge that is a perfect spot to fish for striped bass and huge crappie, and we usually have it all to ourselves because all the poisonous cottonmouths (aka N. rhombifer, N. fasciata, N. sipedon, and very occasionally the super poisonous T. proximus) are all over the place. It's pretty amusing. I can't tell you how many people have nearly lost it when they've seen me catch one, especially if the snake manages to nail me, as watersnakes are good at doing.
Then there is the ever popular story about "Dog Days." I'm at a loss as to what was the basis for forming this myth, and it surprises me that so many people believe it. Supposedly there are a few days during spring when all snakes shed their skin at the same time and are especially venomous and aggressive, often to the point of chasing anyone that comes near. Can't figure out exactly where this one comes from...but it's very annoying nonetheless.
Lastly is the incredibly persistant myth that baby snakes are more venomous than adults. I've had herpers and college professors relate this story to me, so it must be even more persistant than all the rest.
I bet there have been no other group of animals throughout history that have had so much hatred and myth given to them than snakes. Some cultures place then on a deistic level, but all seem to give them supernatural abilities for one reason or another. Too bad there aren't more cultures like India where they are revered.
-Chance