Q, I assume when you wrote "The black snake bit on the heel appear in both White and Black Song" that you mean folk songs from American {USA} White people and folk song from American Black people.

As to why the poor black snake has such a bad reputation, maybe because many more people were shoeless then [because of poverty]and since black snakes were prevalent [more prevalent?], people were ][more?]worried about getting bit by a black snake. From the words of these songs, I gather that black snakes {or any other kind of snake?} more often bites people on the heel than anywhere else {since the heel is the closes part of the body to the ground}.

See this excerpt about fear of encountering snakes in Florida from an online book I found through googling 'black snake bite on heel":

"It has often been said that a rattlesnake is a gentleman and will not strike without warning you. Those people have probably never looked one in the eyes when he was cocked and primed and ready for business. I would not trust anything (or anybody) with eyes as beady as a rattlesnake's are. Do not forget a snake spends his time out in the rain and on cold ground and is likely to develop an arthritic personality! They will usually warn you when they feel that it is to their best interest to do so. Genesis 3: "I will put enmity between you and the woman, and between your seed and her seed. He shall bruise your head and you shall bruise his heel." A snake with his tummy full of rabbit or squirrel is not nearly as anxious to strike you as a hungry one would be. One of the greatest dangers is in stepping over a log or surprising one...

The cutting of palm buds has for generations been a partial livelihood for a few people around here. They cut all winter and sell to a central depot where the buds are packed and shipped to the northern markets, where they are used on Palm Sundays. This could be dangerous work, for you have to be continually looking up instead of studying the ground. We haven't sold any long poles or wide chisels lately so maybe they are not cutting the buds out of tall trees anymore. Garland Strickland told me he was looking up when something hit his boot and when he looked down, there was a rattle snake. He backed up and pulled off his boot to find that the snake had hit the boot where it was reinforced and the fang did not go through. Then he took a stick and killed the snake...

Quite often you hear people say that when you see black snakes, you will see no rattlers because a black snake can and will kill a rattler. I have heard people tell of seeing a battle between the two species. Their explanation was that the black snake was a constrictor and wrapped itself around the rattler, pulling it apart. I can think of nothing less appealing to me than to be wrapped around a rattler, but then, I am not a constrictor..,

I suppose if it had not been for the rattlers in Florida, there would not be any game or much of anything else left in the woods. Fear keeps many people out of the forest and maybe that is a good thing.."

http://historicaltextarchive.com/books.php?op=viewbook&bookid=69&cid=10

"Them Good Ole Days at Mayport and the Beaches"