Black snakes in North America-
Pilot Black Snake- also called Rat snake and Rattlesnake Pilot. It vibrates its tail like a rattlesnake, but is not venomous. Eats mice, birds, eggs, etc. A constrictor. Up to 8 feet in length.
East coast; Maryland, etc.

Black racer- Canada to Florida. Fast and agressive, up to 6 feet long. Vermin destroyer. Bites, but not poisonous. Often confused with the Pilot Black Snake. It can be tamed, and was one of the snakes sometimes kept by old time grocers to keep down rats and mice.

Lots of myths about both.
In the Sea Islands of South Carolina, there is a story about Buh Rabbit capturing a child-eating black snake (Library of Congress recordings). I heard it some time ago and don't remember the details.
The tale may have come from Africa; In Georgia, Joel Chandler Harris collected the story of "The "Cunning Snake," About an 'Afficky' woman and her child, the child is taken by the snake in revenge because the the woman was taking the snake's eggs. The woman finds the snake, cuts it open, and rescues the child. "Nights with Uncle Remus," 1883.

Some of the snakes called 'black snakes' in Australia, Africa and elsewhere are venomous.