Black Racer Snake vs. Cottonmouth

black racer snake vs cottonmouth

Written by Brandi Allred

Updated: September 26, 2023

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Key Points:
  • Despite being pretty venomous, cottonmouths are not generally deadly to humans. Non-venomous black racers are comparatively harmless to people.
  • Cottonmouths can be active at all hours of the day and night, whereas black racers only hunt during the daytime.
  • Cottonmouths can be various shades of brown, and black racers are all black with some markings.

The United States is home to many snake species. In the eastern half of the country, you can find snakes of one species or another just about anywhere you go. This is especially true for two of the eastern United States’ most common species of snake; cottonmouths and black racers

Like all snakes, cottonmouths (Agkistrodon piscivorus) and black racers (Coluber constrictor) are ectothermic, meaning they need the sun to warm their bodies. They both eat their food whole and prey on many of the same species. And, they occur in many of the same regions and habitats, leading some to confuse the two species for one another. Cottonmouths and black racers may eat many of the same things, and live in many of the same places, but only one of them can inflict a dangerous bite on humans.

Here, we’ll learn how to tell the difference between a cottonmouth and a black racer. We’ll start by analyzing their distinct appearances, then go over the preferred habitats of each species. Then, we’ll take a look at each snake’s behavior, and what they eat. Finally, we’ll explore which species is venomous, and which presents the greater threat to humans.

Comparing Black Racers vs. Cottonmouth Snakes

Black Racer vs Cottonmouth
Black racers and cottonmouths are two of the most common snakes in North America
CategoryBlack RacerCottonmouth
Appearance Thin with a narrow headLarger with a heavy body
Habitat Across the majority of America. Lives in Maine on the East Coast and is found across the Rockies on the West CoastMostly confined to the South, enjoys living near aquatic environments.
BehaviorOnly hunt during the dayAre opportunistic hunters that will look for prey day and night
DietSmaller prey that includes small mammals, eggs, amphibiansLarger prey that can include fish, crayfish, snakes, baby alligators
Venom Non-venomousVenomous
Are water moccasins poisonous or dangerous

Cottonmouths are also known as water moccasins.

The Key Differences

The most important difference between black racers and cottonmouth snakes is that cottonmouth snakes are venomous while black racers are non-venomous. Beyond that key difference, black racers are thinner with a more narrow head and cottonmouths live in more aquatic habitats. Let’s dive into all the differences between these two snakes in more detail.

Appearance

Cottonmouths are widely known as water moccasins, whereas black racers are alternately known as North American racers, or simply racers. The biggest visible difference between the two is in the heaviness of their bodies. Where water moccasins are large, heavy-bodied snakes with big heads, black racers are thin, graceful snakes with narrow heads.

southern black racer slithering through brush

Black racers have blueish-black bodies with pale throats.

As their name suggests, adult black racers are almost entirely black, or bluish-black. They have white markings on their chins and throats, and red eyes with round pupils. Young racers, however, have gray scales with distinct orange splotches. In contrast, cottonmouths range from yellow-brown to red-brown and generally have diamond-like patterning. Water moccasins tend to grow darker as they age, but never gain the all-black look of racers.

Habitat

While black racers can be found as far north as southern Maine, cottonmouths prefer life in the south. They occur mostly in lowland areas no farther north than Virginia. Both species extend as far west as eastern Texas.

Locally, cottonmouths prefer moist environments with at least a seasonal supply of freshwater. They’re most common in swamps and floodplains, or near rivers and lakes. Black racers, in contrast, have little preference when it comes to habitat. They make themselves at home everywhere from mountainous zones to flatlands to the edges of urban areas. Racers are extremely common, and people often encounter them just outside of towns and cities.

Behavior

Black racers and cottonmouths have very different ways of birthing their young. Female black racers lay between 1 and 36 eggs during the summer, they hatch in the late summer or early fall. In contrast, cottonmouths actually keep their eggs inside their bodies. The eggs hatch inside the females, who then give birth to live young snakelings. Neither species provides much parental care after that, and many young snakes never make it to adulthood. 

Cottonmouth Snake

Cottonmouths are named for the white insides of their mouths.

Another characteristic setting these two species apart is their active hunting hours. Water moccasins are opportunistic hunters who will take prey at any time of day or night. Unlike cottonmouths, black racers only hunt during the day, they’re known as diurnal snakes. Further, black racers actually vibrate the tips of their tails to mimic rattlesnakes, something cottonmouths don’t do.

When threatened, black racers are much more likely to flee than are cottonmouths. Their impressive speed and their ability to climb trees make escape an effective strategy for the black racer. When people encounter a black racer, it will most likely make a run (or slither?) for it, but when attacked or cornered, it can deliver a nasty but non-venomous bite.

While the black racer slithers away, the water moccasin will actually stand its ground, baring its open mouth to its attacker. This is where the cottonmouth gets its name, from the snowy white interior of its mouth.

Diet

Both black racers and cottonmouths enjoy varied diets. Both species hunt for prey on both land and in the water, though the black racer, being a smaller-bodied snake, is limited to smaller prey. Water moccasins eat fish, crayfish, amphibians, reptiles, smaller snakes, turtles, birds, rodents, turtle eggs, and baby alligators. Black racers eat small rodents such as mice and race, fish, amphibians, smaller snakes, reptiles, and turtles, in addition to birds, bird eggs, and insects.

When it comes to hunting, both cottonmouths and black racers employ two different, opportunistic methods: ambush, and active foraging. 

Venom

Though you don’t want to get bit by either species, a bite from a cottonmouth is much more serious than a bite from a black racer. Why do you ask? Well, the cottonmouth doesn’t just have a sparkling white mouth, it also has large, hollow fangs connected to double venom glands in its cheeks. Inside those venom glands lies the water moccasins’ secret weapon: hemotoxic venom capable of killing small animals in minutes. 

Close up of a southern black racer

Black racers are venomless, though they will bite if threatened.

So, while the cottonmouth uses venom to kill its prey, the black racer, being venomless, is forced to rely on other means of incapacitating and killing. For black racers, the name of the game is in overpowering their prey. Cottonmouths simply strike and bite, then back off and wait for the creature to die. Black racers, however, have to force their prey to the ground, where they either slam it into something hard or suffocate it to death.

What Are the Benefits of Black Racer Snakes?

One key benefit of black racer snakes is they can help with pest control in their habitats. They are valued for assisting in reducing rodent populations because they can hunt and consume large numbers of mice and rats in the area.

These snakes can often be found in residential neighborhoods and thrive where garbage is nearby as that attracts their prey. They can also live near farms and agricultural areas.

Keeping down the amount of rodents is an important as mice and rats can destroy food sources such as crops and cause damage to property, including electrical wiring.

Another benefit of black racer snakes eating mice and rats is decreasing the risk of exposure for residents of their habitats to diseases carried by rodents. Rats’ droppings can cause people to become sick with a range of illnesses. Rodents are also primary carriers of ticks, which spread diseases such as Lyme Disease in humans.

Black racer snake in grass

Black racers can help humans by reducing rodent populations in residential areas.

Which Is More Dangerous?

If you’re afraid of snakes, you’re probably afraid of black racers and cottonmouths, regardless of the fact that only one of them is venomous. Cottonmouths are far more dangerous than black racers, but, they’re still extremely unlikely to kill a human. For both species, bites on humans only occur in cases of extreme threat to the snake. For example, if they’re stepped on, or if a person tries to pick them up, or even attack them. 

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About the Author

Brandi is a professional writer by day and a fiction writer by night. Her nonfiction work focuses on animals, nature, and conservation. She holds degrees in English and Anthropology, and spends her free time writing horror, scifi, and fantasy stories.

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