Cottonmouth Size Comparison: Just How Big Do These Snakes Get?

Cottonmouth snakes are a species of pit viper that deliver a painful and venomous bite. These semi-aquatic snakes are sometimes known as water moccasins.

The western cottonmouth was once classified as a subspecies of the cottonmouth. However, recent studies revealed no significant genetic differences between the eastern and western cottonmouth. This leaves only the two species: Florida cottonmouth and northern cottonmouth.

Over 4,000 species of snakes exist on this planet, and less than a quarter of them are venomous. They come in all different shapes, sizes, and colors, and some can be difficult to distinguish from others. So how large do cottonmouths get compared to other similar snakes?

Florida Cottonmouth Snake

There are two different types of cottonmouth snakes. The first type is the eastern cottonmouth snake (Agkistrodon conanti), often referred to as the Florida cottonmouth. As its name suggests, the eastern cottonmouth primarily makes its home throughout the state of Florida and in southern Georgia.

Florida cottonmouth snakes are not notably long. According to the Virginia Department of Wildlife Resources, the eastern cottonmouth grows to average lengths of 2-4 feet but can be as long as six feet. For reference, a 4-foot specimen would be the same length as the width of a hockey net!

The eastern cottonmouth enjoys slow-moving water such as lakes, marshes, and swamps. They have thick, muscular bodies and are are typically olive brown, dark brown, or black in color.

In general, adult cottonmouths typically weigh 3-4 pounds, but reports have been made of a Florida cottonmouth in Marion County weighing as much as 10 pounds. That’s about the same weight as an average house cat!

Northern Cottonmouth Snake

The second cottonmouth species is the northern cottonmouth (Agkistrodon piscivorus). While the northern cottonmouth is also associated with bodies of slow-moving water, they have a much wider range than the eastern cottonmouth.

Northern cottonmouth snakes are primarily found in southeastern states such as Florida, Georgia, Alabama, Mississippi, Louisiana, and Arkansas. However, the northern cottonmouth may also appear in southeastern Missouri and Kansas, as well as parts of Tennessee and Kentucky.

The northern cottonmouth is similar in size to the eastern cottonmouth. They are typically 3-4 feet in length but have been known to reach lengths of more than six feet, according to the Missouri Department of Conservation. Like the eastern cottonmouth, the northern cottonmouth usually doesn’t weigh more than 3-4 pounds, or about the same weight as a 2-liter bottle of soda.

Female vs Male Cottonmouths

In general, male cottonmouth snakes are larger than females. Both males and females are around 2-4 feet in length, but males have been known to sometimes exceed 5 or 6 feet. Average male cottonmouths weigh less than three pounds, while the average female is less than a pound in weight.

Cottonmouth Snakes and Human Interactions

Although cottonmouths may have a reputation for being aggressive, research indicates that these snakes are shy and prefer not to initiate an attack. The Orianne Society reports a study of cottonmouths by Gibbons and Dorcas (2002) that showed these creatures rarely bit in self-defense.

The cottonmouths tested did not try to bite researchers who simply stood beside them, and less than 20% tried to bite when physically stepped on. Even out of the snakes who were picked up, only 36% attempted to bite researchers.

Largest Recorded Cottonmouth Size

As mentioned earlier in this article, reports of a massive 10-pound cottonmouth have been made but never verified. The largest cottonmouth ever recorded was found near the Virginia-North Carolina border, in an area known as the Dismal Swamp Region. According to a 1990 review, the cottonmouth was 74 inches (or a little over 6 feet) long.

In 2021 an abnormally large cottonmouth was also spotted in North Carolina. Frederick Boyce, who is based at the N.C. Aquarium at Pine Knoll Shores, reported to The News and Observer that the snake was “in excess of 5 feet” long.

“Snakes over 6 feet of any kind are rare, and for cottonmouths truly exceptional. This one is definitely on the upper end somewhere,” Boyce told the outlet. A video of the snake posted to Facebook also earned comments about the creature’s large head.

Boyce suspected the cottonmouth to be a male around 10 years of age. “Cottonmouths tend to be heavy-bodied snakes and aren’t usually known for length,” Boyce continued. “Even a three-foot-long cottonmouth can seem to be a lot larger than it is because they are so girthy.”

Size Comparisons to Other Venomous Snakes

The cottonmouth snake is endemic to the southeastern United States. Other common venomous snakes in the US are copperheads and rattlesnakes.

Copperheads are typically smaller in both length and girth than cottonmouths. Their average length is 2-3 feet and they only weigh 4-12 ounces. Unlike cottonmouths, copperheads prefer dry and rocky environments

There are many different types of rattlesnakes, but one of the most common in North America is the timber rattlesnake. Adult timber rattlesnakes are typically 2.5-5 feet in length. However, the average timber rattlesnake only weighs 1.3-2 pounds.