Copperheads come in a variety of colors, most commonly light brown to rust. All variations have a distinct hourglass pattern of dark cross-bands that flare out at the belly and narrow at the back. Adults are typically two feet in length. They have vertical eye pupils and boxy heads. Their venom is hemotoxic, but it's not very potent and rarely causes fatalities. That being said, the majority of venomous snake bites in the US come from copperheads.
This small member of the rattlesnake family is often mistaken for a baby rattlesnake. They are actually full grown at one to two feet. They do have a rattle, but it's too small to be seen or heard from a distance. They are generally slate-gray in color with a reddish stripe down the backbone and black cross bands. The venom potency and the size of snake make it hard for them to deliver enough venom to kill a human. They also have vertical eye pupils and boxy heads.
Cottonmouth / Water Moccasin
The Cottonmouth is a large bodied snake whose head is wider than its body. They come in shades from black, to brown, to dark olive and everything in between. Younger snakes have an hourglass pattern. As they get older, the pattern fades and they appear solid-colored. They are known locally as an aggressive snake. Their aggressive reputation may not be well earned. Cottonmouths will often stand their ground when encountered by coiling and opening their mouths to show the "cotton" inside. This is a warning to get away. A truly aggressive snake would not give such a warning before striking. On the other hand, if you're close enough to see their cotton mouth, back away because this behavior is a pre-strike warning. They also have vertical eye pupils and boxy heads.