There's no such thing as a "poisonous" snake at all. A poison is a substance you must swallow or inhale in order for it to be harmful. Some snakes have venom, which is different from a poison because it must be injected directly into the bloodstream to be harmful, and often is used mainly to subdue prey and start the digestive process.
In the US, we do not have any black snakes which are venomous, period, yellow belly or not. Any species of snake which would fit that description would be a harmless species.
In the US, we do not have any black snakes which are venomous, period, yellow belly or not. Any species of snake which would fit that description would be a harmless species.