how to tell if a snake is poisonous by color
Questions About Snakes

How to Determine if a Snake is Venomous

Non-venomous snakes live alongside humans without posing any significant health risk. But a bite from a venomous snake that you didn’t realize was hiding in leaves can be dangerous or even fatal.

How can you tell if a snake is venomous? Most venomous snakes in America are pit vipers and share some characteristic traits. They have triangular heads, slit-like pupils, and heat-sensing “pits” near their nostrils. However, the venomous coral snake is an elapid and does not share these traits. They have red-yellow-black bands.

There are other ways of identifying venomous snakes, such as scale formations. Let’s examine these identification methods and explain which venomous snakes they actually apply to. We’ll also share the exceptions to these rules, which have the potential to cause confusion.

Which Venomous Snakes Live in the United States?

Venomous snakes inject venom into their prey when biting them.

They’re often, wrongly, called “poisonous snakes.” Venom caused damage when injected into the skin, whereas poison harms you when you consume it.

There are many types of venomous snake species in the world, from the spiky Saharan Sand Viper to the hooded King Cobra. Today, we’re focusing on the venomous snakes found in the wild in the contiguous United States. Here’s some information on how snakes create venom.

Though there are many species, all North American venomous snakes fall into one of four groups.

1) Rattlesnakes

Rattlesnakes are pit vipers (of the subfamily Crotalinae). There are currently 36 known species of rattlesnake, according to the Integrated Taxonomic Information System.

You might have heard some of them referred to as “sidewinders” and “massasaugas.” The only contiguous U.S. state free from native rattlesnakes is Rhode Island.

Crotalus viridis helleri

Though there are many species and subspecies of rattlesnake, they’re all venomous, and they all have similar features.

Of course, the most well-known is the characteristic “rattle” at the end of their tail. It comprises several hollow segments made of keratin (like our fingernails). As they vibrate their tails, these segments collide together, making a rattling sound.

2) Cottonmouths

“Cottonmouth” is a common nickname for Agkistrodon piscivorus, another pit viper. They are also known as water moccasins or “gapers.” The nicknames of “gaper” and “cottonmouth” come from their threat display of gaping open-mouthed at predators.

They’re native to the southeastern United States. You won’t find a cottonmouth farther north than Virginia or farther west than Texas.

Agkistrodon piscivorus

Cottonmouths typically live in the water, though they can move around on land. Their habitats include streams, marshes, swamps, and lakes.

They aren’t the only type of snake you might find in the water, however. There are many non-venomous snakes which live in the waters of North America, such as the northern water snake (Nerodia sipedon).

3) Copperheads

Copperheads, of the scientific name Agkistrodon contortrix, belong to the same genus as cottonmouths. They are also native to the southeastern states, though copperheads can be found farther north than cottonmouths.

According to the Department of Environmental Conservation, they have even been reported in upstate New York. The nickname “copperhead” comes from their coppery, orange-brown coloring.

Agkistrodon contortrix

Although copperheads and cottonmouths belong to the same genus, they are distinct species. Copperheads, unlike cottonmouths, reside in forests and rocky areas as well as some swamps. For this reason, they are sometimes known by the nickname “dry land moccasin.”

4) Coral Snakes

Coral snakes are the only venomous snakes in North America which are not vipers. They’re part of the family Elapidae, and are incredibly colorful, with red, yellow and black bands.

Their appearance differs drastically from the three other types of snake we’ve mentioned.

types of venomous snake in America

There are dozens of different species of the coral snake, though only three are native to North America. These are the Texas coral snake, the Arizona coral snake, and the eastern (or common) coral snake.

The eastern coral snake covers Louisiana, Mississippi, Alabama, Georgia, Florida, South Carolina, and North Carolina. Coral snakes reside in Arizona and New Mexico. Texas coral snakes have been reported in Texas, Louisiana, Arkansas, and Oklahoma.

So, now that you’re familiar with the four types of venomous snake in the U.S., let’s learn how to identify them.

What Shape Are a Venomous Snake’s Eyes?

You may have heard that you can tell a venomous snake from a non-venomous snake by its eyes. It’s said that venomous snakes, like rattlesnakes, have vertical slit-like pupils (like a cat). Non-venomous snakes, on the other hand, have round pupils (like humans). So, is this true?

For pit vipers, which make up the majority of venomous species in North America, this is a sound rule. Rattlesnakes, copperheads, and cottonmouths all have slit-like pupils. The vast majority of non-venomous species do indeed have rounded pupils.

Unfortunately, the pupil-shape rule is not valid for 100% of North American venomous snakes. There is one exception: the coral snake. All three US-native species of coral snake are Elapids, not pit vipers, and therefore they have round pupils.

It’s not clear why. Most snakes with rounded pupils are diurnal (hunt in the daytime), whereas slit pupils indicate a nocturnal snake. However, coral snakes are nocturnal, so it’s a bit of a mystery.

There are also some non-venomous snakes in the U.S. with slit pupils. Snakes in the family Boidae typically have slit pupils, and there are two species native to America: rubber boas and rosy boas.

So, eye shape alone isn’t a good enough indicator of a venomous snake.

How to Tell if a Snake is Poisonous By its Skin

Now we’ve looked at the snake’s eyes, let’s move on to its body. There are two main elements to a snake’s skin: color, and scale formation.

1) Color

You may be wondering how to tell if a snake is poisonous by color. Unfortunately, it’s not easy. Many species of both venomous and non-venomous snake in the U.S. have similar coloring.

For camouflage, many snakes are some variation of brown, grey, black or cream. Rattlesnakes and cottonmouths are examples of this. They’re often patterned (banded or blotched), but so are many other non-venomous species. Copperhead snakes are also banded but in tan and coppery colors.

Coral snakes, on the other hand, are brightly colored. They have bands of black, yellow and red. Unfortunately, so do many other snakes, such as king snakes.

To be sure it’s a coral snake, look at the color order. Coral snakes always have red bands touching yellow bands. King snakes, on the other hand, have red touching black. “Black and yellow, kill a fellow; red and black, venom lack.

There is one non-venomous snake which does not conform to this rhyme: the shovel-nosed snake. In its case, red touches yellow. Unlike the coral snake, though, the shovel-nosed snake’s colored bands do not extend around its body.

2) Scale Formation

Do you know how to tell if a snake is poisonous by its belly?

It’s all in the scales. If you flipped a snake over (we don’t recommend this!), you’d see a long line of belly scales. Somewhere near the tail, one scale will be larger than the others. This is the anal scale, which covers the cloaca (which the snake poops from).

In many non-venomous snakes, the subcaudal scales (below the anal scale) will be divided into two rows. However, many venomous snakes such as pit vipers only have one row of scales, all the way down to the tail tip.

What’s the problem with this method? It requires you to flip the snake over, and examine its underside. You should never touch a snake which you find in the wild, particularly if you’re not sure whether it’s venomous.

Other Signs That a Snake is Venomous

Other than their eyes and skin, there are four other indicators that a snake is venomous. However, be cautious, because these rules don’t apply to every snake. Let’s look into them in more detail.

1) Heat-Sensing Pits

There’s a reason pit vipers are named such. They have an extra sense: the ability to detect the body heat of nearby animals. To do this, they use deep heat-sensing pits which are located in their rostrum (snout). When you look at a pit viper’s face, you’ll see one facial pit near each nostril.

Most non-venomous species of snake, such as garter snakes, do not have these pits. Therefore, identifying a pit is a good way of telling whether you’ve encountered a venomous snake. However, there are some exceptions.

Coral snakes (Elapidae family) aren’t pit vipers, yet they are still highly venomous.  For this reason, they’re a notable exception to the pit rule. You’ll never see a pit on the face of a coral snake, but this isn’t an indication that it’s non-venomous.

Some non-venomous snakes have heat-sensing pits, too, such as pythons. However, their pits are smaller, and near their lips. The only pythons found in the U.S. are Burmese pythons and African rock pythons, which have been established in Florida.

2) Head Shape

The head shape rule is a well-known one. The idea is that venomous snakes have wide, almost triangular-shaped heads, with comparatively slim necks. By contrast, non-venomous snakes have oval, elongated heads with no distinct necks. So, how accurate is this assertion?

Again, this rule applies well to pit vipers. Rattlesnakes, cottonmouths, and copperheads all have distinctly wide heads and slimmer necks. And most species of nonvenomous snake, true to the rule, have narrower heads. However, it’s not an accurate rule to follow, for the following reasons.

This is another rule which the coral snake does not conform to, being of the family Elapidae. Unlike pit vipers, they do not have wide, triangular-shaped heads. Coral snakes’ heads are narrow and oval, and their necks are the same width.

The head-shape rule also fails to apply to many non-venomous species. Harmless water snakes and rat snakes have narrow heads most of the time. However, when they feel threatened, they can flatten their heads and make them appear wider.

This is a defense mechanism, making them appear more like a viper. So, for this reason, the head shape rule is not a very accurate one to go by.

3) Tail Rattle

All species of rattlesnake have a characteristic rattle. It appears as a hollow, segmented section at the end of the tail. When a rattlesnake feels threatened, it vibrates its tail, causing the well-known rattling noise. If the snake you’re looking at has a rattle, that’s an excellent indicator to stay well away.

Of course, only rattlesnakes have rattles. Cottonmouths, copperheads, and coral snakes do not possess this unique anatomical structure. But some rattlesnakes also lack the ability to rattle.

A rattlesnake can only rattle its tail when there are at least two segments that can collide. If a rattlesnake is too young to have grown a second segment, or if it’s lost its rattle to a predator, it won’t be able to rattle.

Some non-venomous snakes can also vibrate their tails, mimicking the sound of a rattlesnake. Such snakes include rat snakes, king snakes, and gopher snakes.

They developed this ability as a defense mechanism, to fool predators into thinking they’re venomous. They have no rattle apparatus but vibrate their tails in the grass to mimic the sound.

Even venomous cottonmouths and copperheads can shake their tails when confronted, despite lacking a rattle.

4) Bite Mark

This final indicator is the only 100% accurate way to tell whether a snake is venomous. Unfortunately, it involves allowing the snake to bite you, and examining the wound.

Venomous snakes, such as vipers, have two large fangs for injecting venom. Non-venomous snakes have a series of much smaller teeth. If a bite leaves two large, deep holes, fangs are probably responsible. A horseshoe of tiny, shallow holes indicates that the snake was non-venomous.

If you do meet an unfamiliar snake in the wild, always assume that it’s venomous. Even if you think you recognize the snake as being harmless, don’t get too close – it could cost you your life.

According to the CDC, around five people die from venomous snakebites per year in the USA. While that’s not many, you certainly wouldn’t want to end up one of them. Of course, some snakes are less likely to bite you than others.