Nerodia taxispilota

Geographic Range

Brown water snakes, Nerodia taxispilota , are a native species of the Nearctic region in North America, specifically, the southeastern United States. Brown water snake range includes the entirety of Florida, but it is limited to Coastal Plains and Piedmont regions of Alabama, Georgia, South Carolina, North Carolina, and Virginia.

• Biogeographic Regions
• nearctic nearctic
  • native native

Habitat

Due to their semi-aquatic nature and appetite for fish, brown water snakes reside in habitats such as lakes, rivers, banks, and streams. Ideal habitats for brown water snakes exhibit various amenities suitable for basking and hunting, including branches, logs, or vines that hang roughly 2 tp 4 meters above water level. Capture records indicate these snakes remain close to backwater habitats and choose steep banks and the outside bends of rivers, as they present more perch sites. A species common to the coastal plain, elevation is reported to be sea level to 150m.

• Habitat Regions
• temperate temperate
• freshwater freshwater

• Aquatic Biomes
• lakes and ponds
• rivers and streams
• coastal coastal

• Other Habitat Features
• riparian riparian

Physical Description

Brown water snakes are relatively large-bodied, ranging from 50.3 to 174 centimeters in length. The largest specimen ever recorded was roughly 177.8 centimeters long. Brown water snakes have several rows of strongly-keeled, dark brown dorsal scales spanning from head to tail that are suitable for swimming, and ventral scales that are a much lighter shade of brown. Their heads are very wide (relative to their necks) with a pair of eyes and nostrils located abnormally high on their heads, providing a tactical advantage while swimming. The triangular shape of brown water snakes' heads gives them a similar appearance to venomous snakes indigenous to the same regions.

They have between 30 and 34 black squares running down the middle of the dorsum, with identical black squares running down either side. The ventrum of brown water snakes exhibits the same black squares with the addition of numerous black, crescent-shaped markings. Female brown water snakes are longer at maturity.

Although newly hatched snakes have not been documented, late-stage-pregnancy (within a few weeks of birth) females had fully-developed embryos averaging 18.5 cm long. Young snakes are lighter in color.

• Other Physical Features
• ectothermic ectothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• female larger

Development

White et al. (1982) describe developmental stages of brown water snakes. Males produce sperm in late summer months, but mating does not take place until the spring or later. After they mate, females can store the sperm until they ovulate. In a Virginia population, females ovulated in mid-summer and embryos were visible by July. Young, with clutch sizes averaging 28 young, were born in September.

Newly-born brown water snakes range from 7 cm to 18.5 cm in length and have more vibrant coloring than adults. Male adolescents grow and develop much faster than females, reaching sexual maturity at three years of age, or about 50 cm snout-vent length. However, females ultimately grow significantly larger than males and reach sexual maturity between five and six years of age. Like all snakes, these water snakes exhibit indeterminate growth.

Sexes are determined by identifying male and female reproductive organs. Male brown water snakes possess a pair of hemipenes in their tails, giving them a unique size and shape in comparison to the tails of female brown water snakes.

• Development - Life Cycle
• indeterminate growth indeterminate growth

Reproduction

While courting potential female mates, male brown water snakes will rest their heads on the backs of females until they allow the joining of their cloacal openings for insemination. There are no set gestation periods for brown water snakes, so females can potentially mate with multiple partners before actually giving birth. However, a Virginia study found the majority or adult females sharing a similar gestational phase from spring until late summer. In this study, females ovulated in mid-summer (June), and young were at full-term by late August.

• Mating System
• polygynandrous (promiscuous) polygynandrous (promiscuous)

Female brown water snakes breed once a year. Brown water snakes do not have set gestation periods, because pregnancies are dependent on female ovulation rather than deposition of semen. However, regional studies suggest that populations may be in sync during summer months. In Virginia, the majority of adult females were pregnant and at the same gestational phases from June until September, when young were presumed to be birthed.

Females are viviparous and can store semen in their cloaca for extended periods of time in order to build sufficient stores of nutritional fat, as they cannot hunt while they are pregnant. Brown water snakes mate between late February and early May, giving live birth to 20-60 neonates between mid June and early October. Larger females produce larger clutches. In Virginia, the average number of neonates for females at full-term was 28.

All neonates are immediately independent following birth. Male brown water snakes reach sexual maturity at 3 years of age at snout-vent lengths of about 50 cm, while females do not reach sexual maturity until roughly 5 or 6 years of age.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• sexual sexual
• viviparous viviparous
• sperm-storing sperm-storing
• delayed fertilization delayed fertilization

Female brown water snakes have minimal involvement in the protection of their young, as they are independent immediately following birth. Female brown water snakes are unable to hunt effectively while pregnant, so they must prepare by storing large amounts of nutritional fat as nourishment for them and their eggs. Being ovoviviparous, females provide protection for neonates until they are born. Males provide no parental investment beyond mating.

• Parental Investment
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female

Lifespan/Longevity

Not much information is known about the lifespans of brown water snakes because they are particularly hard to capture and study. However, many mark/recapture studies indicate that the average lifespan of brown water snakes is 6.2 years. Although they are relatively long-lived, brown water snakes are often killed because they have similar appearances to highly venomous species that are indigenous to the same regions. Habitat loss also threatens the longevity of brown water snakes because they are piscivorous and cannot survive without nearby freshwater sources providing food and shelter.

Behavior

Brown water snakes are thought to be mostly diurnal but have been found hunting in evening hours, especially when large predators like american alligators Alligator mississippiensis are absent. They can also change activity times seasonally, as nocturnal activity is most reported in mid-summer. As baskers, they are inactive for large parts of the day. They choose habitats that possess access to perching sites, and are often found sunbathing on branches hanging over the water to regulate their body temperatures. Males are found at higher perches than females.

When feeding, these snakes are capable of diving. Captive studies have shown that they can remain submerged for 30 minutes without any harm.

Basking snakes have been anecdotally reported to play dead. When touched while basking, they can even stop signs of breathing. When threatened, their two instinctive responses are to attack or drop off of the branches into the water to escape. Brown water snakes are adept at swimming, so they primarily move through the water.

Males and females are solitary, only interacting when mating. Here, male brown water snakes will rest their heads on the backs of females until they allow the joining of their cloacal openings for insemination.

• Key Behaviors
• arboreal arboreal
• terricolous
• natatorial natatorial
• diurnal diurnal
• nocturnal nocturnal
• solitary solitary

Home Range

Although home ranges are not reported for brown water snakes, Mills et al. (1995) report densities of 0.02 snakes per linear meter of river, or about 1 individual for every 50 m of river. Mills in a later study reported 0.14-0.20 snakes per meter. In mark-recapture studies, adults typically travel less than 250 m between multi-year captures, but few individuals may travel 1 km or more. These snakes are not known to defend territories.

Communication and Perception

Brown water snakes perceive their environment using highly developed senses of smell. Their tongues serve as sensory devices that identify chemical signals in the air given off by potential prey or predators. Tongue-flicking has been observed while they actively hunt underwater, searching under rocks and in crevices.

Brown water snakes also perceive their environments through sight and touch. Subtle vibrations can provide information about their surroundings, similarly to how they receive information through chemical signals. When mating, males and females use touch to signal readiness to mate.

They use vision to hunt, and are seen dropping down from perches directly into the water, capturing a fish.

• Communication Channels
• visual visual
• tactile tactile
• chemical chemical

• Other Communication Modes
• vibrations vibrations

• Perception Channels
• visual visual
• tactile tactile
• vibrations vibrations
• chemical chemical

Food Habits

The two main hunting techniques of brown water snakes include actively foraging for food and ambush hunting. They are primarily piscivorous, feeding almost exclusively on small catfish as large (snout-vent lengths over 60 cm) adults. They catch the snake and carry it in their jaws to land to comsume ti. They are known to eat the fish whole, swallowing it head-first.

There have been uncommon cases of brown water snakes consuming organisms that lie outside of their typical dietary range. They will feed on small lizards, turtles, crayfish, frogs, and other snakes when prey is scarce. In captivity, they refuse nearly all food items except fish.

• Primary Diet
• carnivore carnivore
  • eats terrestrial vertebrates
  • piscivore piscivore
  • eats non-insect arthropods

• Animal Foods
• amphibians
• reptiles
• fish
• aquatic crustaceans

Predation

Brown water snakes are a non-venomous, but they are extremely aggressive when threatened. The shear size and powerful bite of brown water snakes provides suitable protection from predators. If necessary, they will drop from overhanging branches into the water in order to flea from predators or catch prey. The dull coloration of brown water snakes serves to protect them from potential threats, as they cannot be easily spotted from underneath. The dark brown splotches running down their dorsum look similar to sediment on the bed of water sources, so they can move through water undetected.

Known predators of brown water snakes include American alligators ( Alligator mississippiensis ), birds of prey, humans ( Homo sapiens ), and raccoons ( Procyon lotor ). Larger snakes, like cottonmouths ( Agkistrodon piscivorus ), may also prey on them.

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

Brown water snakes consume primarily catfish as adults, but there is no evidence that they regulate populations of those species. Known parasites of brown water snakes are all helminths, an non-taxonomic group that includes worm-like parasites. Reported species include cestodes Proteocephalus perspicua and Ophiotaenia perspicua . Trematodes include Ochetosoma aniarum , Pneumatophilus variabilis , and Styphlodora magna . An acanthocephalan Centrorhynchus conspectus also has been found. Nematodes include those from the genera Terranova , Spiroxys , and Rhabdias

Economic Importance for Humans: Positive

There are no positive economic impacts of brown water snakes on humans.

Economic Importance for Humans: Negative

There are no negative economic impacts of brown water snakes on humans.

Conservation Status

On the IUCN Red List, brown water snakes are categorized as a species of "Least Concern." The U.S. Federal, CITES, and State of Michigan lists all indicate that brown water snakes do not have a special conservation status. Threats to these snakes are human-caused. Humans may kill these snakes, mistaking them for venomous snakes in their range. This has been documented in Virginia. Habitat loss from urban sprawl and water pollution (which affects their prey) also can be threats. There have been reports of these snakes being subjected to radiation in their waters but seem unaffected. They also do not bioaccumulate mercury. Because of the commonality of this species, no conservation measures are in place.

Additional Links

Encyclopedia of Life

Contributors

Michael Sampson (author), Radford University, Alex Atwood (editor), Radford University, Karen Powers (editor), Radford University, Joshua Turner (editor), Radford University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

References

Blem, C., K. Blem. 1990. Metabolic acclimation in three species of sympatric, semi-aquatic snakes. Comparative Biochemistry and Physiology , 97/2: 259-264.

Blem, C., L. Blem. 1990. Lipid reserves of the brown water snake Nerodia taxispilota. Comparative Biochemistry and Physiology , 97/3: 367-372.

Blem, C., K. Killeen. 1993. Circadian metabolic cycles in eastern cottonmouths and brown water snakes. Journal of Herpetology , 27/3: 341-344.

Camp, C., W. Sprewell, V. Powders. 1980. Feeding habits of Nerodia taxispilota with comparative notes on the foods of sympatric congeners in Georgia. Journal of Herpetology , 14/3: 301-304.

Collins, R. 1969. The helminths of Natrix spp. and Agkistrodon piscivorus piscivorus (Reptilia: Ophidia) in eastern North Carolina. Journal of the Elisha Mitchell Scientific Society , 85/4: 141-144.

Densmore, III, L., F. Rose, S. Kain. 1992. Mitochondrial-DNA evolution and speciation in water snakes. Herpetologica , 48/1: 60-68.

Franklin, M. 1944. Notes on the young of the brown water snake. Copeia , 1944/4: 250-250.

Hammerson, G. 2007. "Nerodia taxispilota" (On-line). The IUCN Red List of Threatened Species 2007: e.T63857A12722712. Accessed November 22, 2017 at http://dx.doi.org/10.2305/IUCN.UK.2007.RLTS.T63857A12722712.en. .

Herrington, R. 1989. Reproductive biology of the brown water snake (Nerodia taxispilota) in central Georgia. Brimleyana , 15: 103-110.

Irvine, A., H. Prange. 1976. Dive and breath hold metabolism of the brown water snake. Comparative Biochemistry and Physiology , 55/1: 61-67.

Mills, M. 2002. Ecology and Life History of the Brown Water Snake (Ph.D. Dissertation) . Athens, GA: University of Georgia. Accessed November 22, 2017 at https://getd.libs.uga.edu/pdfs/mills_mark_s_200205_phd.pdf .

Mills, M., C. Hudson, H. Berna. 1995. Spatial ecology and movements of the brown water snake (Nerodia taxispilota). Herpetologica , 51/4: 412-423.

Mitchell, J., G. Zug. 1984. Spermatogenic cycle of Nerodia taxispilota in southcentral Virginia. Herpetologica , 40/2: 200-204.

Selmlitsch, R., W. Gibbons. 1982. Body size dimorphism and sexual selection in two species of water snakes. Copeia , 1982/4: 1974-1976.

Selmlitsch, R., W. Gibbons. 1978. Reproductive allocation in brown water snakes. Copeia , 1978/4: 721-723.

White, D., J. Mitchell, W. Woolcott. 1982. Reproductive cycle and embryonic development of Nerodia taxispilota at the northeastern edge of its range. Copeia , 1982/3: 646-652.

Wright, A., A. Wright. 1957. Handbook of Snakes of the United States and Canada . Ithaca, New York: Comstock Publishers.