Not all black snakes are poisonous. The black rat snake is a large snake, but it is nonvenomous, instead killing its prey through constriction. The Northern black racer snake can be rather bad-tempered, but it too is nonvenomous.
The Eastern indigo snake, which is found in the Southeastern United States, is one of the largest non-venomous snakes in the South, but is far more biddable than the black racer. It also makes a good pet
However, one black snake that is poisonous is the black mamba. It is quite possibly the most poisonous snake in the world. The venom from this snake can kill a human being within 20 minutes, and its bite has been fatal even to grown elephants. The black mamba is found in Africa.
Australia's red-bellied black snake is also venomous, but it rarely bites, preferring to engage in a threat display.
The cottonmouth is also a dangerously venomous snake with a black body. It gets its name because of the white interior of its opened mouth. It's found around water in the American South, and is also called the water moccasin. It's also a pit viper, which means it has special sensory organs in its head that sense heat.