Field Guides

Semi-Aquatic Snakes of Missouri

Though many people fear them, semi-aquatic snakes are fascinating creatures that play a vital role in Missouri ecosystems. Their unique biology sets them apart from other legless animals, such as some species of lizards, which have moveable eyelids, whereas snakes have an immobile scale. 

The anatomy of snakes’ respiratory system is also interesting. Behind the snake’s tongue, they have a small opening called the glottis, which leads to the trachea. The glottis is always closed in a vertical slit, except for when the snake takes a breath. A small piece of cartilage in the glottis vibrates when the breath is expelled, which produces the snake’s hiss. While eating, the snake can extend its glottis out the side of its mouth, so that it can continue breathing while digesting large prey. Most snakes have a small or vestigial left lung, while the right lung is much longer and more functional. The portion of the right lung closest to the head does most of the respiration, whereas the portion closest to the tail functions more like an air sac. 

Depending on the species, snakes can have 200-400 vertebrae. Because of this, they have the flexibility to move forward using a fluid side-to-side motion. They can also travel sideways in a motion called sidewinding. This is typically used on slippery surfaces like sand or mud. When sidewinding, a snake will contract its muscles to hurl its body through the air, moving laterally and maintaining only two points of contact with the ground. There are three other methods that snakes use to move: serpentine, caterpillar, and concertina. Most snakes use the serpentine method, which is the familiar S-shape movement that most people associate with snakes. The snake contracts its neck muscles to move its body from side-to-side. Aquatic snakes prefer this method because the water pushes back against the snake’s motion and propels it forward. On land, snakes will use resistance points such as rocks or sticks to propel themselves forward. The caterpillar method of movement is much slower, and also involves contracting muscles to create curves. However, these curves are up and down rather than lateral. The snake’s ventral scales on the bottom curves grip the ground, allowing the snake to push itself forward. The concertina method of movement is used for climbing. The snake extends its head and grips the surface with its ventral scales, forming tight curves with the middle of its body and pulling its back end up. 

Snakes have a loose lower jaw bone and a moveable upper jaw bone that allows them to swallow their food whole with additional help from their teeth, which curve inward to prevent live prey from escaping. Non-venomous snakes swallow their prey live, whereas venomous snakes inject their prey with venom and eat the corpse.

All snakes can swim, but semi-aquatic snakes gain a majority of their diet from aquatic creatures such as fish, crayfish, amphibians, lizards, and insects and live very near water. 

There are 8 species of semi-aquatic snakes found in Missouri. Of these species only one is venemous.

Western Cottonmouth (Agkistrodon piscivorus leucostoma):

Also known as the water moccasin: the only venemous semi-aquatic snake in Missouri, one of five venemous species in the whole state.  

Physical Characteristics: 30-42 inches long; thick, dark brown-black body with patterns of darker bla and dark underside with light colored blotches, head is noticeably wider than the neck.  

Location in Missouri: Cottonmouths are primarily found in swamps and lakes in southeastern Missouri but can also be found in streams and swampy areas of rivers in the southern Ozarks.

Habits: When it swims its head and back are on the surface of the water.  When it feels threatened it goes into its defensive stance and gapes its mouth wide exposing the white inside, this is how it got its name as “cottonmouth”.  If it is approached in an open area it will go into its defensive stance but it there is cover nearby it will hide.   

Diet: fish, frogs, lizards, rodents, small birds, other snakes, and sometimes small roadkill

Active seasons: The cottonmouth is active from April to October.  It is generally a nocturnal creature but will bask in the sun in the beginning and end of the season.  Mating will happen throughout the active period and babies are most commonly born in August and September.  

(Johnson, 2000) (Briggler et al)

Western Mud Snake (Farancia abacura reinwardtii):

This snake is the subject of two untrue myths.  One, that it can put its tail in its mouth and roll at a great speed.  Two, that the sharp scale at the end of its tail is a poisonous stinger that can kill a person.  

Physical Characteristics: 40-54 inches long; black coloration on the back that spreads to the bright red underside forming bands.  Slightly flattened head and a tail that ends with a sharp scale.

Location in Missouri:  Found in cyprus swamps in the southeast tip of Missouri.  This habitat is in danger and if it is destroyed then this species could be in danger.

Habits: Normally active at night, usually hiding under wet logs or in burrows.  If they are caught they will rarely bite out of defense, but rather try to prick with their tail, wich will cause no harm to a human, or play dead.      

Diet: They mainly eat Lesser Sirens and aquatic amphiuma, salamanders found in wetlands in the central and southern US. (STL Zoo)  Sometimes they will eat other types of salamanders or tadpoles and frogs.  The spine at the end of their tail is used to prod their prey so they unfurl and are easier to eat.

Active Seasons: April-October.  There is little known about the mating habits of this species but sceintists believe they mate in the spring and the eggs will hatch in August or September.       

(Johnson, 2000) (Briggler et al)

Water Snakes

There are five species of water snakes found in Missouri, all part of the genus Nerodia.  They feed mostly in water on fish and amphibians.  In Missouri all water snakes are viviparous, which means they give birth to live young.  The number of offspring correlates with the size of the female  When provoked water snakes will bite but, despite often being mistaken for the cotton mouth, their bite is not venemous and will do no serious harm, they will also excrete a bad smelling liquid that is smeared onto their captors.  When water snakes are in the water they only expose their head to the surface, unlike the cottonmouth whose back is exposed.     (Wallach, 2009)   

Mississippi Green Water Snake (Nerodia cyclopion):

An endangered species in Missouri

Physical Characteristics: 30-45 inches long; dark greenish brown back with a dark grey underside with yellow markings. 

Location in Missouri:  Found in the ever-shrinking natural cyprus swamps in southeastern Missouri.  It was once fairly common in that area but are now endangered in the state.

Habits: Active on warm days; often found hanging in branches over water.  Normally hunts in the evening or at night.  

Diet: fish, salamanders, frogs, small crabs, and crayfish

Active Season: This species is not very well known.  It is thought to be active between March and October.  Mating is thought to happen in April or May and the babies are born in August or September.

Yellow-bellied Water Snake (Nerodia erythrogaster flavigatser)

Physical Characteristics: 30-48 inches.  Dark body with plain yellow belly, no patterns.  

Location in Missouri: Southeastern Missouri, north along the Mississippi River and in the western part of the state.  Found mostly in calm bodies of water like lakes, ponds, and swamps.

Habits: Found basking on logs near/in water or in branches overhanging water.   

Diet: fish, toads, frogs and tadpoles, salamanders, and crayfish.

Active Season:  March – October; mating happens in April and May; babies born in August and September.

Broad-banded Water Snake (Nerodia fasciata confluens)

Physical Characteristics: 22-36 inches.  As the name suggests it has broad bands of dark coloration over a light background, the belly is bright yellow with black marks.  

Location in Missouri: Found in cyprus swamps, lakes, and river sloughs in southeastern Missouri.

Habits: Sunbathes in trees and logs.  During hot weather it is more active at night than in the day.  If cornered it will flatten its body and fight to try to escape, if captured it will bite.

Diet: Fish, toads, frogs and tadpoles

Active Season: March – October; Mating occurs in April and May; babies are born in July, August, and September

Diamond-backed Water Snake (Nerodia rhombifer rhombifer):

The largest species of water snake in Missouri

Physical Characteristics: 30-48 inches; light brown or grey background color with dark diamond shapes outlines with a light color.  Yellow bellied with dark splotches or crecent shapes.  

Location in Missouri: Swamps and marshes throighout the state; mostly found in the southeast, northern, and western parts of the state.

Habits: Nocturnal; will create a pen with its body to catch small fish. 

Diet: Fish (usually dead or slow), toads, and salamanders

Active Season: March – October; mating takes place in April or May, babies are born in August through October. 

Northern Water Snake (Nerodia sipedon sipedon):

The most common water snake in Missouri

Physical Characteristics: 24-42 inches; the back of this snake is grey or brown with darker horizontal bands across the back.  Its belly is cream colored with crescent shaped red or orange splotches bordered by black.

Location in Missouri: Found throughout the northern two thirds of the state in creeks, rivers, ponds, lakes, and swamps. 

Habits: They can be found on branches overhanging water or on logs and rocks near the water.  This snake is mostly nocturnal during hot weather and will hide under rocks and logs during the day.

Diet: Small fish make up a majority if their diet but they are also known to eat amphibians.

Active Season: April – October; Mating takes place in the spring; babies are generally born in August and September.

(Johnson, 2000)

Graham’s Crayfish Snake (Regina grahamii

Physical Characteristics: 18-28 inches; A mute brown or grey back with a yellow stripe down the lower sides and a cream colored belly.

Location in Missouri: Found most places in Missouri, except the Ozarks, in prairie streams, marshes, and ponds.

Habits: They can be found basking in branches hanging above water or hiding under rocks, logs, or in crayfish burrows along the edge of the water.  They generally do not bite when caught but will release a bad smelling substance like the water snakes.   

Diet: Primarily they feed on crayfish that just shed their exoskeletons (soft bodied crayfish), but will sometimes eat frogs and tadpoles. 

Active Season: April – November; Mating happend in April and May; babies are born from July to September.

(Johnson, 2000)

Due to lack of knowledge and fear many semi-aquatic snakes are killed by people who believe them to be venemous cotton mouths.  A majority of snakes are harmless to people, and even if a venemous snake is encountered they will not strike if left alone.  If you encounter any snake, semi-aquatic or otherwise, the best course of action is to leave it alone unless you are with someone who is trained in handling them.  If you are bitten by a snake  and are unsure of the type the best course of action is to seek medical help immediately.  For more information on venemous snakes and first aid see


Briggler, Jeff; Tom R. Johnson. Snakes of Missouri. Missouri Department of Conservation.  

Johnson, Tom R.  Snakes.  The Amphibians and Reptiles of Missouri, Second Edition, Missouri Department of Conservation, 2000.  

Wallach, Van. Water Snake.  Encyclpedia Britannica, Encyclopedia Britannica, inc., Jan 14, 2009., Dec 15, 2016.  

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