Nerodia erythrogaster
Plainbelly Water Snake

Nerodia erythrogaster is divided into a number of subspecies. Nerodia erythrogaster erythrogaster, found from southeastern Virginia through western North Carolina, South Carolina, Georgia, with the exception of the northwest corner, northern Florida and southeastern Alabama with disjunct populations in Maryland and Delaware. Nerodia erythrogaster flavigaster is found in Alabama, northwestern Florida, Mississippi, Louisiana, eastern Texas, southeastern Oklahoma, Arkansas and areas surrounding the junction between the borders of Kentucky, Illinois and Missouri. Nerodia erythrogaster transversa is found in western Missouri through Kansas (except northwestern Oklahoma), Texas, southwestern New Mexico and a disjunct population in northeastern Mexico. Nerodia erythrogaster neglecta is found in southwestern Indiana and the border areas of adjacent states, with disjunct populations in southern Michigan, Indiana, Iowa, and western Ohio. Nerodia erythrogaster bogerti is found in Durango, Mexico. Nerodia erythrogaster alta is found in Zacatecas, Mexico. Nerodia erythrogaster is Nearctic in distribution. (Conant and Collins, 1998; Gibbons and Dorcas, 2004)

Plain-bellied water snakes are semi-aquatic snakes, using both terrestrial and freshwater aquatic habitats. Most subspecies are found in warm temperate regions, but the range of Mexican subspecies extends into tropical climates. Terrestrial habitats used include forests, grasslands, and scrublands. Terrestrial habitats are used as travel corridors, aestivation sites, hibernation sites and occasional feeding sites. Aquatic habitats include ephemeral ponds or temporary pools, permanent lakes and ponds, swamps, bogs, marshes, small rivers, and riverine sloughs. Hibernation primarily occurs in crayfish burrows near wetlands. Feeding primarily occurs in or near ephemeral wetlands, where frogs and toads are abundant. Subspecies of Nerodia erythrogaster do not vary significantly in habitat preferences. Plain-bellied water snakes travel farther from water and use a greater variety of cover types than most other water snakes. Individuals have been found several hundred meters from the nearest water source. Upland corridors are critical travel areas. Use of these corridors has brought this species into agricultural and suburban areas where mortality can be high. Loss of wetlands and terrestrial corridors has put many populations under severe stress. ("Northern Population of the Copperbelly Water Snake (Nerodia erythrogaster neglecta) Recovery Plan", 2008; Aldridge, et al., 1995; Conant and Collins, 1998; Ernst and Ernst, 2003; Gibbons and Dorcas, 2004; Harding, 2006; Roe, et al., 2003)

Plain-bellied water snakes are large, typically solid-colored water snakes. Dorsal coloration varies among black, gray, olive-gray, brown, and pink. Some specimens show faint crossbars and lighter colored snakes can exhibit dark dorsal blotches. Plain-bellied water snakes can be distinguished from other species by the near-uniform coloration of the dorsum and both the ventral and subcaudal scales (except in some specimens of N. e. neglecta).

Nerodia e. erythrogaster is a uniform shade of brown dorsally that can be tinted with red, gray or green. The venter ranges from orange to pink. Nerodia e. flavigaster is gray to olive-gray dorsally and ventrally ranges from orange-yellow to a very pale yellow or white. Nerodia e. neglecta is dorsally black or dark brown and the venter ranges from yellowish-orange to orange-red or scarlet. The dark dorsal coloration can extend to the ventral scales, especially in the posterior region. Nerodia e. transversa ranges from gray to brown dorsally and often shows a blotchy pattern. The venter is yellow to yellow orange. Nerodia e. alta is dorsally olive-brown sometimes with dark blotches. The venter ranges from pale yellow to orange. Nerodia e. bogerti is dorsally pink to pink-brown sometimes with dark blotches. The venter varies from yellow to pink-yellow. (Conant and Collins, 1998; Ernst and Ernst, 2003; Gibbons and Dorcas, 2004)

Juveniles of all subspecies exhibit mid-dorsal blotches alternating with lateral blotches. Dorsal coloration is lighter than that of adults. The venter is uniformally colored. (Conant and Collins, 1998; Gibbons and Dorcas, 2004)

Other species of the genus Nerodia often have ventral spotting or other markings, a heavier dorsal pattern, and smaller eyes than Nerodia erythrogaster. (Conant and Collins, 1998; Gibbons and Dorcas, 2004)

Average adult mass is 286 g for males and 516 g for females. Average length of adults is 76 to 122 cm. The record length to date for this species is 163.6 cm (total length). This species is sexually dimorphic, with the female growing to a larger size. Plain-bellied water snakes are ectothermic. (Conant and Collins, 1998; Gibbons and Dorcas, 2004; Michigan Natural Features Inventory, 2007)

Plain-bellied water snakes are viviparous, fertilization is internal, and sex is determined genetically. One study found a significant relationship between amount of food consumption and growth rate from birth to seven months of age. (Gibbons and Dorcas, 2004)

In the United States, mating reportedly takes place from April through early June and usually occurs once per year for females, though they may be able to store viable sperm for almost two years. Courtship often takes place in "cords," or groups. Cords typically include one adult female and several males (4 to 7 in one study), though it is unclear if more than one male is normally able to successfully fertilize the female. Courtship involves much tongue flicking and following of the female by males. Males then align with a female to match positions of the head and tail. The snakes then often coil around each other with tails entwined. Mating cords were observed in flooded forest wetlands with less than 15 cm of standing water. Another instance of mating took place in a pond near the shoreline. Woody debris was observed near the breeding site. (Ernst and Ernst, 2003; Harding, 2006; Lacki, et al., 2005; Michigan Natural Features Inventory, 2007)

After mating, the gestation period in this viviparous species is typically 3 to 4 months. Copulation occurs between May and June and births occur from August through October. The average number of offspring produced is 17.8 and can range from 2 to 55. Litter size is often significantly smaller in Mexican (tropical) subspecies. Mass at birth ranges from 3.5 g to 10.9 g with an mean mass of 6.4 g. Neonates measure 18 to 30 cm in total length. Males and females reach sexual maturity at between 3 to 4 years of age. (Aldridge, et al., 1995; Ernst and Ernst, 2003; Gibbons and Dorcas, 2004; Harding, 2006)

There is no post-parturition parental care. However, females supply embryonic nutrients in the form of yolk and perhaps directly through the bloodstream (established for some natricine snakes). Viviparity is an evolutionary method of protecting offspring which involves provisioning and sacrifice. During gestation the female may be less capable of feeding and maintaining full mobility and therefore may be more susceptible to predators. (Ernst and Ernst, 2003; Vitt and Caldwell, 2009)

Captive individuals of Nerodia erythrogaster have been found to live about 8 to 15 years. ("An Age Database: Nerodia erythrogaster", 2009; Ernst and Ernst, 2003; Harding, 2006)

Plain-bellied water snakes are semi-aquatic snakes that are active during the day. They are mostly solitary, although mating can occur in groups of one female with several males. The active period over most of their range in the United States is from March to early November. In the southern parts of their range, they have longer seasonal activity periods than in the north. Plain-bellied water snakes travel through upland areas seeking prey near ephemeral wetlands, permanent wetlands, and rivers. Hibernation primarily occurs in animal burrows, stream banks, rock piles, or (especially in N. e. neglecta) abandoned crayfish burrows. During high water periods these snakes may become almost entirely submerged. Some individuals will hibernate in upland areas. Upland areas are also used for aestivation. Resource partitioning with other water snakes (Nerodia) may be the evolutionary reason behind reliance on upland habitats. Evidence of this is seen in the variation of diets between related species with overlapping ranges. ("Northern Population of the Copperbelly Water Snake (Nerodia erythrogaster neglecta) Recovery Plan", 2008; Ernst and Ernst, 2003; Gibbons and Dorcas, 2004; Harding, 2006; Kingsbury and Coppola, 2000; Michigan Natural Features Inventory, 2007)

Plain-bellied water snakes are the most terrestrial and mobile species in the genus Nerodia. In one study these snakes were found to travel between wetlands an average of 9 times in one season. The mean distance moved per shift was 143.1 m. The mean distance that these snakes traveled away from wetlands was 95.9 m, with a maximum distance of several hundred meters. Movements of individuals of various subspecies have been measured and do not vary significantly. These movements within large wetland complexes expose Nerodia erythrogaster to dangers such as human encounters and road crossings. This has been a major factor in population declines, especially for the northern subspecies N. e. neglecta. A minimum recommended territory size is 0.8 km^2. However, territorial area can range from 0.03 km^2 to 0.5 km^2. ("Northern Population of the Copperbelly Water Snake (Nerodia erythrogaster neglecta) Recovery Plan", 2008; Gibbons and Dorcas, 2004; Roe, et al., 2003)

Specific communication systems in Nerodia erythrogaster have not been thoroughly researched. In general, snakes use chemical communication (via the vomeronasal organ) at a distance and tactile signals for close range communications. Skin pheromones produced from the dorsal surface of females have been proven important in reproduction. Cloacal pheremones are used in defense and trailing. This is most likely the source of the odorous musk used when this species is attacked. Most snakes use tactile signaling in courtship. Vitt and Caldwell (2009) identified three phases of courtship that seem to fit the behavior of Nerodia erythrogaster. These are tactile chase, tactile alignment and intromission coitus. Chemical cues may be used when males are identifying each other in order to establish dominance. Snakes are capable of sensing vibrations and airborne acoustical signals (hearing). (Ernst and Ernst, 2003; Vitt and Caldwell, 2009)

Plain-bellied water snakes are carnivores that feed extensively on ectotherms. Northern populations are more specialized predators on frogs and toads, whereas southern populations are sometimes more piscivorous. Crustaceans and carrion make up a small part of the diet. Confirmed prey includes species in the following families: Catostomidae, Centrarchidae, Cyprinidae, Esocidae, Fundulidae, Ictaluridae, Percidae, Poeciliidae, Ambystomatidae, Amphiumidae, Sirenidae, Bufonidae, Hylidae, Ranidae. These snakes travel long distances to reach prey in ephemeral wetlands. They will pursue prey if escape is attempted. (Ernst and Ernst, 2003; Gibbons and Dorcas, 2004; Harding, 2006)

Snakes in the genus Nerodia will flatten themselves or flee when detected. If cornered, they will strike fiercely. When attacked they will discharge an odorous musk in self defense. They are preyed on by a large number of medium to large aquatic, terrestrial, and avian predators. (Ernst and Ernst, 2003; Harding, 2006)

Plain-bellied water snakes are prey items for many kinds of birds, mammals, turtles, snakes, and fish. They are predators that feed on frogs and toads, insects, and fish, thus helping to keep prey populations in balance. They undoubtedly act as hosts to various internal and external parasites. (Ernst and Ernst, 2003; Gibbons and Dorcas, 2004)

Plain-bellied water snakes are important members of the ecosystems they inhabit. Since northern populations (particularly N. e. neglecta) are in decline and listed as threatened or endangered, research activities and wildlife viewing are in high demand. ("Northern Population of the Copperbelly Water Snake (Nerodia erythrogaster neglecta) Recovery Plan", 2008; Ernst and Ernst, 2003)

There are no adverse effects of plain-bellied water snakes on humans. In areas where they are threatened, certain individuals, such as land developers, may see Nerodia erythrogaster as an economic liability due to their protected status. Special permits and assessments may be necessary in some areas. If handled, these snakes will bite, but are no danger to people who leave them alone. ("Northern Population of the Copperbelly Water Snake (Nerodia erythrogaster neglecta) Recovery Plan", 2008; Harding, 2006)

Nerodia erythrogaster neglecta is listed as threatened by the U.S. Fish and Wildlife Service and endangered in the states of Michigan, Ohio, and Indiana. (Michigan Natural Features Inventory, 2007)

An area for further research is to determine the effectiveness of wildlife underpasses. This could be a solution to one of the major causes of mortality, which is road crossings. When mitigation is required, the focus should be on construction of ephemeral wetlands as opposed to the traditional large deep water wetlands. Land acquisitions to protect this species should be large in size, preferably several hundred acres, and should contain a diversity of wetland types and travel corridors. Wetlands should be < 200 m apart and should be surrounded by a buffer area. ("Northern Population of the Copperbelly Water Snake (Nerodia erythrogaster neglecta) Recovery Plan", 2008; Roe, et al., 2006; Roe, et al., 2003)