The plain-bellied water snake is a widespread member of the water snake genus Nerodia.
This article will give you an overview of the species. This includes its life cycle, diet, identification, taxonomy, and more. Read on and learn about these wonderful animals.
Adult plain-bellied water snakes are heavy-bodied snakes that are between 29.9 and 48 inches (76-122 cm) long. Females are larger than males and weigh almost double.
Females weigh 18.2 ounces (516 grams) on average while males weigh only 10 ounces (286 grams) as adults. They are typically dark in color with little to no patterning still visible.
The color of the back and belly varies depending on the location. The back color can be brown, gray, black, olive-grey, olive green or pink.
Some lighter animals can have visible crossbars, dorsal spots, or blotches depending on the region.
The belly is always unpatterned, which helps set it apart from other species. The belly color will change over its range, leading to slightly different common names depending on the area.
The belly color can be in many shades of pink, yellow, white, orange, red, greenish gray and many shades in between. The neck is not well defined from the head. The eyes are large, placed high on the head, and have a round pupil.
Juveniles tend to be lighter than adults and have visible patterning. They have obvious strongly patterned dorsal botching that alternates with lateral dark colored blotching:
The belly is the same color as the adult. Neonates are 7-11.8 inches (18-30 cm) long on average and weigh 0.12-3.8 ounces (3.5-10.9 grams). They grow somewhat slowly and reach sexual maturity sometime between 3 and 4 years of age.
Plain-bellied water snakes can be told apart from other Nerodia species by their unpatterned bellies. Other species also have smaller eyes and may have heavier patterning on the back.
Tell apart a Plain bellied water snake from a Copperhead
They can be told apart from copperheads by their darker color and a smaller difference between the head and neck.
Copperheads (Agkistrodon contortrix) also tend to have a triangle or hourglass-shaped marking along the sides on a lighter reddish-brown background.
Copperheads have a thick, blunt, triangular head with a scale over the eye that makes it hard to see the eye from directly above.
They also have a vertical pupil while the plain-bellied water snake has a round pupil. Copperheads also have a heat-sensing pit under the eye that plain-bellied water snakes lack.
Young copperheads also have a yellow or olive green tail tip while baby plain-bellied water snakes have a tail that matches their general coloration.
Tell apart a Plain bellied Water-snake from a Cottonmouth
Cottonmouths (Agkistrodon piscivorus) can be easy to confuse for a watersnake and both are commonly mistaken.
The head and neck are two major differences. First, cottonmouths have the viper face with a scale over the eye which means you can’t see the eye from above.
They also have slit pupils, a pit under the eye, and typically have dark markings on the face.
Cottonmouths also have a very white mouth that they show when they gape it open during their defensive display.
Cottonmouths also have a thick, blocky head that is triangular and distinctly larger than the neck. They have very thick bodies and short tails.
Plain-bellied water snakes have less distinct heads, round pupils, no heat pit, lack facial markings, and do not have the brow scale over the eye.
Juvenile cottonmouths also have a brightly colored tail tip, which helps set them apart from plain-bellied water snakes.
McCranie, James R. “Nerodia erythrogaster.” Catalogue of American Amphibians and Reptiles (CAAR) (1990) is an excellent overview of the species. It includes a description, distribution, and even lists the fossil record for the species.
Natural habitat and Distribution
The plain-bellied water snake is currently considered to be one widely ranging species. The southern extent of their natural habitat range is Zacatecas, Mexico.
Plain bellied watersnakes geographic range extends in central north america, north into the United States with populations throughout much of the eastern, southern, and central portions of the country.
These are semi-aquatic snakes. They spend most of their time near bodies of water such as temporary or permanent ponds, lakes, cypress swamps, bogs, small rivers, riverine sloughs, and marshes, looking for humid weather.
They will travel between bodies of water to hunt and may switch hunting grounds over 9 times in a single season. They use upland corridors including forests, grasslands, and scrublands to travel and hide during the warmer months.
They travel the furthest to reach new hunting grounds of any Nerodia species. The average travel distance is 500 feet, but some snakes will go much further to reach a new area.
They have somewhat large territories that can cover over a third of a mile square. This can mean that they need to cross roads or other areas of human activities to reach new food sources.
This has threatened them since, in some areas, the bodies of water they rely on are separated or even destroyed by human activity.
The primary diet of the plain-bellied water snake is fish, frogs, and toads. They have been known to take carrion and crustaceans on occasion.
Northern populations tend to eat more frogs while southern populations eat more fish. Juveniles will eat more fish and switch to consuming more frogs once they are large enough to hunt the local species.
Plain-bellied water snakes have been known to catch fish that seem very large in comparison to the snake. As you can see on the photo above, they will also eat smaller prey items even if the animal is a large adult.
Fish, Frogs and Toads
Plain-bellied water snakes consume a wide range of fish, frogs, and toads according to Mushinsky, Henry R., and James J. Hebrard. “Food partitioning by five species of water snakes in Louisiana.” Herpetologica (1977): 162-166.
This study was conducted south of Baton Rouge, Louisiana. Plain-bellied water snakes in the study were analyzed to see what prey they ate. Small and medium fish species made up 12% of the diet.
Toads made up 20.5% and frogs made up 66.2% of the diet. The remainder was made up of tadpoles. This means that at least in some parts of their range, plain-bellied water snakes rely on anurans for a large part of their diet.
While they are generalists, a healthy supply of frogs is needed for this species.
Mushinsky, Henry R., James J. Hebrard, and Darrell S. Vodopich. “Ontogeny of water snake foraging ecology.” Ecology 63.6 (1982): 1624-1629 further confirms the importance of frogs and toads in the diet of adult plain-bellied water snakes.
Juveniles rely on fish and switch to frogs as they grow. The shift occurs once the snake exceeds a snout-vent length of 50cm or 19.76 inches.
While females are larger, males are still large enough to also switch their diet to frogs. Another factor to note is that plain-bellied water snakes will also eat smaller prey items.
One interesting paper is Bassett, Lawrence G., Armani R. Price, and Michael RJ Forstner. “Attempted predation by a Plain-bellied Watersnake, Nerodia erythrogaster (Forster, 1771), on the cyprinid fish Carassius auratus (Linnaeus, 1758) in Hays County, Texas, USA.” Herpetology Notes 14 (2021): 1291-1293. Goldfish have been released into the wild and have established populations in much of the United States. However, they are not always eaten by native predators.
Before this observation, only the common water snake (Nerodia sipedon) and the diamondbacked water snake (Nerodia rhombifer) have been reported to eat goldfish in the wild.
In this case, a juvenile plain-bellied water snake was seen trying to consume a goldfish that it had dragged onto the bank of the pond.
The snake pulled the fish back into the water when it noticed that it was being observed and eventually returned to eating its prey. This indicates that the species will consume a wide variety of prey.
Reproduction and Life Cycle
Plain-bellied water snakes are diurnal animals that are active for much of the year depending on the location. In the northern ranges, they may only be active from late March to early October or even less time.
In warmer areas, they may be active during most of the year. The breeding season is from April to June in much of the United States.
As you can see on the photo above, plain-bellied water snakes breed in groups of one female and multiple males, though it is unknown if more than one male gets to fertilize the female.
A courting male will flick his tongue and follow the female. He will try to align his head and tail with the female. If she is receptive, she will allow for copulation and both snakes will coil together with the tails entwined.
Fertilization is internal and females carry the young and give birth. It is currently unknown if nutrients are supplied to the embryos solely with yolk or if some nutrients are delivered from the mother’s bloodstream.
Gestation and litters
Gestation takes three to four months and young are typically born between August and October. Litter sizes can range from 2 to 55 young and the average litter size is 17.8.
Once born, mothers do not provide any care to the babies. Males do not have any part beyond mating. The growth rate of the babies depends on how much they eat during the first year of life.
It takes males and females three to four years to reach sexual maturity. The average wild lifespan has not been established, but captive plain-bellied water snakes live between 8 and 15 years.
Kofron, Christopher P. “Reproduction of aquatic snakes in south-central Louisiana.” Herpetologica (1979): 44-50examines the reproduction of female snakes in south-central Louisiana.
The reproductive systems of female snakes in the Atchafalaya River Basin were examined to see the date of ovulation and potential gestation times.
Plain-bellied water snakes ovulate during May and June, and likely breed around this time. Young are typically born in September at least.
Since a neonate was caught in April, there is likely another breeding early. The study notes that plain-bellied water snakes can become active in January in the region. Many species of snakes will breed not long after they start eating again after the cold season.
Kingsbury, Bruce A., and Christopher J. Coppola. “Hibernacula of the copperbelly water snake (Nerodia erythrogaster neglecta) in southern Indiana and Kentucky.” Journal of Herpetology 34.2 (2000): 294-298 describes the hibernacula used by the plain-bellied water snake in Southern Indiana and Kentucky.
Hibernacula are where many snakes that brumate spend the winter. The snakes were tracked to their hibernacula using radio transmitters implanted under the skin of the animal.
Because of the size of the transmitter, only larger animals were used in the study. This does mean it won’t include small juveniles.
The snakes tended to stay close to the waterways and habitats they live in during the warmer months in one study area. Some of these hibernacula were very likely to be flooded.
At another site, the plainbelly water snake used crayfish burrows to brumate in. Even when the burrows flooded, the snakes stayed put. They survived just fine. Most animals will not use the same burrow every year. They also brumate alone.
Taxonomy & Subspecies
The scientific name of the plain-bellied water snake is Nerodia erythrogaster.
They are in kingdom Animalia, phylum Chordata, class Reptilia, order Squamata, suborder Serpentes, family Colubridae, genus Nerodia, species erythrogaster. This means they are vertebrate animals.
They are reptiles, specifically snakes. They are in the colubrid family of modern snakes. There were multiple recognized subspecies:
- Nerodia erythrogaster bogerti
- Nerodia erythrogaster alta
- Nerodia erythrogaster flavigaster (Yellow bellied watersnake)
- Nerodia erythrogaster transversa
- Nerodia erythrogaster erythrogaster (Red Bellied watersnake)
- Nerodia erythrogaster neglecta
However, Makowsky et al. (2010) didn’t find evidence that these subspecies are valid. They do not have enough genetic variation to be evolutionarily distinct.
They are also not geographically circumscribed. While there has been some specialization depending on the location, this is not enough to make them distinct subspecies. It is best considered a single, very widespread species.
Overall, the species is doing well. Since it is found over such a large range, it is unlikely to go extinct. However, local populations can be at risk from human activity.
It is considered to be endangered in the states of Michigan, Ohio, and Indiana. Development and road fatalities are some of the major threats.
Wildlife underpasses are being considered as a way to help protect the species.
Construction or protection of ephemeral wetlands can also help conserve the species along with large portions of wetlands and travel corridors placed under protection.
In 2014 a captive female produced two healthy offspring via parthenogenesis (without interaction with male partner).
Frequently Asked Questions
These are some frequent questions about plain-bellied water snakes. If your question isn’t answered, please leave it in a comment below.
Plain-bellied water snakes are amazing north american water snakes that live over a huge range.
If you have seen one in the wild, we would love to hear about it in the comments below. If you have any other questions, please leave them in the comment section as well.