What is a diamondback snake?

Answer 1

Rattlesnake.Rattlesnakes are a group of venomous snakes, genera Crotalus and Sistrurus. Most rattlesnakes mate in the spring. All species give live birth, rather than laying eggs. The young are self-sufficient from birth. They do not need their mother after birth, and the mother does not remain with her young. All rattlesnakes to some extent possess similar characteristics to their cousins the pit vipers.

The western diamondback has a wide, stout body, short tail and a triangular head. These snakes possess a pit between their nostrils and their eyes that's a heat-sensing organ to detect warmblooded prey. Hollow fangs for envenomation are possessed. Muscles above the teeth control the amount of venom released. They average one and a half meters long and weigh between six to seven kilograms. They can be several different colors, but are usually a yellowish gray with a black diamond pattern and pale white borders extending down the back. Their rattle at the tip of their tail is black.

Note, the western diamondback rattlesnake accounts for the most fatalities in North America.
A rattler.

Answer 2

It could be the diamondback water snake which is a nonvenomous colubrid found in the central United States and northern Mexico. While not venomous it is a nasty tempered snake, quick to bite. You may also be referring to the diamondback rattlesnakes of which there are two species - the eastern diamondback, found in the southeastern United States and the western diamondback found in the southwestern United States and Mexico. Both are venomous and can grow quite large, approaching or exceeding seven feet in length.