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Nerodia fasciataSouthern Water Snake

By Annette Califano

Geographic Range

Nerodia fasciata is a nonvenomous species with three distinct subspecies (N. f. fasciata, N. f. confluens, and N. f. pictiventris). Collectively, these three subspecies are referred to as southern water snakes and they are native to the southeastern United States. The range of N. fasciata includes eastern Texas, southeastern Oklahoma, Arkansas, Louisiana, southeastern Missouri, western Tennessee, western and coastal Mississippi, southern Alabama, southern Georgia, Florida, and most of the Coastal Plain of North and South Carolina. (Bartlett and Bartlett, 2005; Conant and Collins, 1998; Dorcas and Gibbons, 2004)

Habitat

Nerodia fasciata is a generalist when it comes to freshwater habitats, and individuals are found in rivers, streams, lakes, reservoirs, swamps, or small wetlands. Individuals can tolerate an average salinity that is less than 1.0 ppt, they will not survive in any saltwater environment. (Bartlett and Bartlett, 2005; Dorcas and Gibbons, 2004; Ernst and Ernst, 2003)

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams

Physical Description

A distinguishing feature of southern watersnakes is a dark stripe that extends from the eye to the angle of the jaw, but other coloration is variable. The base color can be gray, tan, dark olive, or black. The belly is typically off-white or white. The dorsal cross bands, which cover the entire body length, can also vary in color. Subspecies are distinguished based on banding patterns, color patterns, and ventral scale numbers. Nerodia f. fasciata has dark ventral markings that are square-shaped and more than 128 ventral scales. Nerodia f. confluens has dark body bands that are wider than N. f. fasciata, and only 11 to 17 bands are present along the length of the body as a result. Individuals of N. f. confluens also have rectangular, reddish-brown spots on the sides of the venter. Nerodia f. pictiventris can have dark brown, black, or reddish bands, dark lateral spots between the bands, and wavy, reddish transverse lines on the belly. Neonates are more vividly colored and patterned than adults.

Adult southern watersnakes range from 61 to 106.7 cm in length, whereas neonates tend to be about 24 cm long. These snakes exhibit sexual dimorphism in which females are typically longer and heavier than males. They have a standard metabolic rate of 1.21cm3/h at 25°C. (Bartlett and Bartlett, 2005; Dorcas and Gibbons, 2004; Ernst and Ernst, 2003; Hopkins, et al., 2004; Hopkins, et al., 1999; Semlistch and Gibbons, 1982)

  • Sexual Dimorphism
  • female larger
  • Range mass
    113.5 to 246.9 g
    4.00 to 8.70 oz
  • Range length
    61 to 106.7 cm
    24.02 to 42.01 in
  • Average basal metabolic rate
    1.21 cm3.O2/g/hr

Development

Young southern watersnakes are born alive. Females carry their young during the spring and early summer and give birth in the months of July, August, September, and October. While the females carry their young, the developing embryos are nourished via a placenta. The gestation period averages about 79 days, depending on the temperature. It has been suggested that the gestation period shortens at higher elevations but there is not enough research to support such an assertion. Embryos cannot tolerate temperatures beyond the 21 to 30°C range for the entire gestation period; however, the sex of the neonates is not dependent on temperature. After birth, young snakes can reach sexually maturity in about two to three years. Individuals grow throughout their lifetime but their growth rate decreases with age. (Ernst and Ernst, 2003; Kofron, 1979; Viets, et al., 1994)

Reproduction

A female will start ovulating from early May to mid-June after awakening from a period of hibernation. Males produce sperm in the fall that will be ready for summer mating. Individuals start mating from early April to mid-June. Males have been seen congregating in the water before a period of mating, but there is not enough field evidence to suggest that this species is indeed polyandrous. Males pursue females. Once a female is caught, the male will crawl anteriorly onto her back until the head of the female is reached. When the head is reached, the male will pin it down and then he will position his tail beneath that of the female, bringing their two vents together. Copulation generally lasts about 60 minutes. (Dorcas and Gibbons, 2004; Ernst and Ernst, 2003)

Breeding season varies with locality and subspecies. In general, the breeding period extends from early April to mid-June. Females ovulate from May to June after awakening from a period of hibernation. They undergo vitellogenesis, which includes rapid yolk deposition and follicle growth. Males produce sperm in the fall, but they mate after emerging from the hibernation period. Copulation takes at least 60 minutes. As far as gestation period is concerned, it is assumed to become shortened at higher elevations; however, there is not enough research to support such an assertion. The average gestation period is about 79 days. Larger females tend to have larger litter sizes. Females give birth as early as July and as late as October. The average litter size is about twenty, but there is no evidence suggesting that females can have two litters in one season. (Dorcas and Gibbons, 2004; Ernst and Ernst, 2003; King, et al., 2009; Kofron, 1979; Krysko and King, 2010; Lorenz, et al., 2011)

  • Breeding interval
    Southern watersnakes breed once per year.
  • Breeding season
    Southern watersnakes breed from early July to late October.
  • Average number of offspring
    20
  • Average gestation period
    79 days
  • Range age at sexual or reproductive maturity (female)
    2 to 3 years
  • Range age at sexual or reproductive maturity (male)
    2 to 3 years

There is no information about parental investment in southern watersnakes in the literature. However, females invest substantially in protecting the young in their cloaca during development and providing resources to the embryo. After birth, the young become independent. (Ernst and Ernst, 2003)

Lifespan/Longevity

In general, southern watersnakes mature by the age of 3 and can live up to 7 or 8 years. The lifespan of southern watersnakes is dependent on the quality and the quantity of their food. A male and female member both survived captivity for 3 years and 3 months. In general, individual southern watersnakes do not live long in captivity. (Ernst and Ernst, 2003; Nielsen, 2011)

  • Range lifespan
    Status: wild
    8 (high) years
  • Average lifespan
    Status: captivity
    3 years

Behavior

The literature suggests that southern watersnakes are similar in behavior to other water snakes. Their movement patterns are suggested to be very similar to northern watersnakes, Nerodia sipedon. They use lateral undulatory movement and sidewinding for crawling on the ground. Most watersnakes swim with their bodies fully submerged in water. Individuals also flick their tongues in order to gather chemical stimuli from the environment. They are active both during the day and at night. In winter, they can be found hibernating beneath logs or rocks or in burrows. During periods of extreme drought, southern watersnakes will leave the area, possibly to find a more suitable aquatic habitat. It has been suggested that they are driven away from an area affected by drought primarily because of the reduced water levels as well as reduced levels of aquatic prey. Although their numbers may initially drop during a drought period, these snakes recover substantially afterwards because these snakes have a high fecundity rate. (Daghfous, et al., 2012; Dorcas and Gibbons, 2004; Ernst and Ernst, 2003; Seigel, et al., 1995; Willson, et al., 2006)

Home Range

Home range size is not reported in the literature.

Communication and Perception

Snakes use their sense of sight, smell, and touch to navigate. They use visual and olfactory cues to recognize predators, prey, and their environment. Southern watersnakes flick their tongue in order to collect smells from the environment, such as the scent of a nearby food item. There have not been many studies, though, that focus solely on communication and perception in this species, but snakes generally use pheromones in order to attract mates. (Daghfous, et al., 2012; Ernst and Ernst, 2003; Mason, et al., 1989)

Food Habits

Southern watersnakes are dietary generalists that undergo ontogenetic changes from eating primarily fish as juveniles to eating mainly frogs or large fish as adults. Young stay on a fish diet until they are about 6 months old. The type of fish and amphibians that they consume will largely depend on the particular area they inhabit, but some prey include American eels (Anguilla rostrata), pirate perch (Aphredoderus sayanus), banded pygmy sunfish (Elassoma zonatum), American pickerel (Esox americanus), topminnows (Fundulus species), western mosquitofish (Gambusia affinis), least killifish (Heterandria formosa), white catfish (Ameiurus catus), bluegill sunfish (Lepomis macrochirus), spotted sunfish (Lepomis punctatus), rainwater killifish (Lucania parva), bass (Micropterus species), golden shiners (Notemigonus crysoleucas), southern toads (Anaxyrus terrestris), spring peepers (Pseudacris crucifer), gopher frogs (Lithobates capito), and red-spotted newts (Notophthalmus viridescens). On occasion, they prey on small turtles, small snakes, birds, earthworms, and crayfish. The enlarged gape of snakes allows them to consume large prey, but southern watersnakes have a difficult time ingesting prey items that are relatively heavy, short, and wide. (Dorcas and Gibbons, 2004; Ernst and Ernst, 2003; Vincent, et al., 2006)

  • Animal Foods
  • birds
  • amphibians
  • reptiles
  • fish
  • terrestrial worms
  • aquatic crustaceans

Predation

Southern watersnakes are primarily preyed on by other snakes, great blue herons (Ardea herodias), and alligators (Alligator mississippiensis). In order to avoid predation, individuals escape into the water, enlarge their posterior head region, bite repeatedly, or secrete a foul musk. They are also cryptically colored, which makes them harder to find for predators. (Dorcas and Gibbons, 2004; Vincent, et al., 2006)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Southern watersnakes control populations of fish and amphibians. Florida watersnakes (N. f. pictiventris) are carriers of the parasite hemogregarines (Hepatozoon species), which is one of the most common blood parasites among snakes. (Vincent, et al., 2006; Wozniak, et al., 1998)

Commensal/Parasitic Species
  • hemogregarines (Hepatozoon species)

Economic Importance for Humans: Positive

Southern watersnakes are important predators of amphibians and fish in aquatic habitats. (Vincent, et al., 2006)

Economic Importance for Humans: Negative

There are no known adverse effects of these snakes on humans.

Conservation Status

Southern watersnakes are not threatened. They are abundant in appropriate habitat and dietary generalists. Southern watersnakes are an ideal species to study in order to assess environmental conditions, such as water quality. For instance, they have been used as focal studies in research studying the effects of exposure to coal combustion wastes on metabolic rates. (Dorcas and Gibbons, 2004; Hopkins, et al., 1999)

Other Comments

Nerodia fasciata is often mistaken for venomous cottonmouths (Agkistrodon piscivorous) despite the differences in their physical appearance. As a result, many southern water snakesare mistakenly killed by humans. (Krysko and King, 2010)

Contributors

Annette Califano (author), The College of New Jersey, Keith Pecor (editor), The College of New Jersey, Tanya Dewey (editor), University of Michigan-Ann Arbor.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

diurnal
  1. active during the day, 2. lasting for one day.
ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

female parental care

parental care is carried out by females

fertilization

union of egg and spermatozoan

freshwater

mainly lives in water that is not salty.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

hibernation

the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.

indeterminate growth

Animals with indeterminate growth continue to grow throughout their lives.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

marsh

marshes are wetland areas often dominated by grasses and reeds.

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

ovoviviparous

reproduction in which eggs develop within the maternal body without additional nourishment from the parent and hatch within the parent or immediately after laying.

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

piscivore

an animal that mainly eats fish

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

young precocial

young are relatively well-developed when born

References

Bartlett, R., P. Bartlett. 2005. Guide and Reference to the Snakes of Eastern and Central North America. Gainesville, FL: University Press of Florida.

Conant, R., J. Collins. 1998. Reptiles and Amphibians: Peterson Field Guides. New York: Houghton Mifflin Company.

Daghfous, G., M. Smargiassi, P. Libourel, R. Wattiez, V. Bels. 2012. The function of oscillatory tongue-flicks in snakes: insights from kinematics of tongue-flicking in the banded water snake (Nerodia fasciata). Chemical Senses, 37/9: 883-896.

Dorcas, M., J. Gibbons. 2004. North American Watersnakes. University of Oklahoma Press.

Ernst, C., E. Ernst. 2003. Snakes of the United States and Canada. Washington: Smithsonian Institution.

Hopkins, W., J. Roe, T. Philippi, J. Congdon. 2004. Standard and digestive metabolism in the banded water snake, Nerodia fasciata fasciata. Comparative Biochemistry and Physiology, 137: 141-149.

Hopkins, W., C. Rowe, J. Congdon. 1999. Elevated trace element concentrations and standard metabolic rate in banded water snakes (Nerodia fasciata) exposed to coal combustion wastes. Environmental Toxicology and Chemistry, 18: 1258-1263.

King, R., R. Jadin, M. Grue, H. Walley. 2009. Behavioural correlates with hemipenis morphology in New World natricine snakes. Biological Journal of the Linnean Society, 98: 110-120.

Kofron, C. 1979. Reproduction of aquatic snakes in south central Louisiana. Herpetologica, 35: 44-50.

Krysko, K., F. King. 2010. "Online Guide to Snakes of Florida" (On-line). Florida Museum of Natural History. Accessed October 01, 2013 at http://www.flmnh.ufl.edu/herpetology.

Lorenz, O., B. Horne, N. Anderson, A. Cheek. 2011. Reproductive physiology of the broad banded water snake, Nerodia fasciata confluens, in southeastern Louisiana. Herpetological Conservation and Biology, 6/3: 410-421. Accessed October 01, 2013 at http://www.herpconbio.org/Volume_6/Issue_3/Lorenz_etal_2011.pdf.

Mason, R., H. Fales, T. Jones, L. Pannell, J. Chinn, D. Crews. 1989. Sex pheromones in snakes. Science, 245: 290-293.

Nielsen, A. 2011. "Water Snake" (On-line). Accessed October 30, 2013 at http://www.watersnake.net/.

Seigel, R., J. Gibbons, T. Lynch. 1995. Temporal changes in reptile populations: effects of severe drought on aquatic snakes. Herpetologica, 51(4): 424-434.

Semlistch, R., J. Gibbons. 1982. Body size dimorphism and sexual selection in two species of water snakes. Copeia, 4: 974-976.

Viets, B., M. Ewert, L. Talent, C. Nelson. 1994. Sex-determining mechanisms in squamate reptiles. The Journal of Experimental Zoology, 270: 45-56.

Vincent, S., B. Moon, R. Shine, A. Herrel. 2006. The functional meaning of “prey size” in water snakes (Nerodia fasciata, Colubridae). Oecologia, 147: 204-211.

Willson, J., C. Winne, M. Dorcas, J. Gibbons. 2006. Post-drought responses of semi-aquatic snakes inhabiting an isolated wetland: insights of different strategies for persistence in a dynamic habitat. Wetlands, 26/4: 1071-1078.

Wozniak, E., S. Telford, D. DeNardo, G. McLaughlin, J. Butler. 1998. Granulomatous hepatitis associated with Hepatozoon sp. meronts in a southern water snake (Nerodia fasciata pictiventris). Journal of Zoo and Wildlife Medicine, 29/1: 68-71.

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