Systematics: John Edwards Holbrook originally described this species as Coluber taxispilotus in 1838 (Holbrook, 1838a) from the "seaboard of South Carolina . . . [and] the neighbourhood of the Altamaha river in Georgia." Baird and Girard (1853) first used the generic name Nerodia for this species. However, Natrix was used as the genus for many years for North American water snakes. Most authors in the Virginia literature (e.g.. Cope, 1900; Dunn, 1936; Werler and McCallion, 1951; Burger, 1958; Hardy, 1972; Mitchell, 1974b) used the combination Natrix taxispilota until Rossman and Eberle (1977) determined that the generic name should be replaced by Nerodia. Subsequent authors have used the current nomenclature. No subspecies are recognized.

Description: A large, heavy-bodied snake reaching a maximum total length of 1,766 mm (69.5 inches) (Conant and Collins, 1991). In Virginia, maximum known snout-vent length (SVL) is 1,325 mm (52.2 inches), and maximum total length was reported by Werler and McCallion (1951) to be 1,745 mm (68.7 inches). In this study, tail length/total length was 18.9-28.6% (ave. = 23.7 ± 2.1, n = 51).

Scutellation: Ventrals 131-143 (ave. = 137.1 ± 2.2, n = 179); subcaudals 59-86 (ave. = 74.5 ± 5.1, n = 139); ventrals + subcaudals 197-224 (ave. = 211.4 ± 6.3, n = 139); dorsal scales strongly keeled, scale rows usually 29-31 at midbody (75.7%, n = 173), but may be 25-28 (20.8%) or 32-34 (3.5%); anal plate divided; infralabials 12/12 (39.5%, n = 177), 11/11 (21.5%), 11/12 (19.2%), or combinations of 9-13 (19.8%); supralabials 8/8 (84.8%, n = 178) or other combinations of 7-10 (15.2%); loreal scale present; preoculars usually 1/1; postoculars 2/2 (32.0%, n = 178), 3/3 (36.0%), 2/3 (29.2%), or 3/4 (2.8%); temporal scales highly variable: 2+312+3 (23.0%, n = 174), 2+3/2+4 (20.1%), or other combinations of 1-5 (56.9%).

Coloration and Pattern: Dorsum brown with a series of 22-36 (ave. = 25.4 ± 1.6, n = 179) square chocolate-brown to black blotches along midline of body and tail, alternating with similar blotches on each side; middorsal blotches about 8.5 scale rows wide and 2.5 scales long, with anterior and posterior projections at corners, forming a crude H shape; lateral blotches 3-5 scales long and occurring on scale rows 1-10; venter yellowish with an irregular pattern of dark-brown pigment that occurs in patches; large areas of black peppering occur on venter; head uniformly brown with a somewhat darker snout; chin brown; infralabials light brown bordered in dark brown; venter of neck cream with some brown peppering and dark-brown spots; little change in color occurs in preservative. This snake has a relatively long head that is wider than the neck.

Sexual Dimorphism: Females were larger than males in SVL (females 707-1,325 mm, ave. = 918.7 ± 135.4, n = 51; males 462-835 mm, ave. = 628.3 ± 97.2, n = 81) and reached a larger total length (to 1,595 mm; males to 1,051 mm). Sexual dimorphism index was 0.46. Tail length/total length was lower in females (18.9-24.5%, ave. = 22.7 ± 1.2, n = 33) than in males (20.6-28.0%, ave. = 25.6 ± 1.9, n = 16). In a Chesterfield County population, males averaged 561.6 ± 130.5 SVL and 182.1 ± 115.4 g body mass, whereas gravid females averaged 936.1 ± 138.0 SVL and 1,034.1 ± 445.2 g body mass (Blem and L. Blem, 1990). White et al. (1982) found that males averaged 608 ±112 mm SVL and females averaged 738 ± 201 mm SVL in samples from the same area. Sexual dimorphism indices were 0.67 and 0.21, respectively. The heaviest female known was one collected on 22 January 1929 at Sandbridge, City of Virginia Beach, that measured 1,259 mm SVL and weighed 2.76 kg (F. M. Uhler, pers. comm.). The average number of ventral scales (males 138.5 ± 1.9, 135-143, n = 87; females 135.8 ± 1.7, 131-140, n = 89) and subcaudal scales (males 78.2 ± 4.3, 59-83, n = 66; females 70.8 ± 2.4, 65-76, n = 71) were slightly higher in males than females. This pattern was repeated in the average number of ventrals + subcaudals (males 216.6 ± 4.4, 197-224, n = 66; females 206.4 ± 2.9, 199-213, n = 71). The average number of dorsal blotches was nearly identical between sexes (males 25.5 ± 1.9, 22-36, n = 87; females 25.3 ± 1.2, 22-28, n = 89). There are no sexual differences in pattern and color.

Juveniles: Juveniles are identical to adults in pattern and color. At birth, juveniles were 210-218 mm SVL (ave. = 215.3 ± 2.1, n = 19), 279-296 mm total length (ave. = 288.0 ± 5.2), and 9.1-12.1 g body mass (ave. = 11.1 ± 0.6).

Confusing Species: Within the range of N. taxispilota, Nerodia sipedon is smaller on average, has complete dark crossbands on the anterior body, half moons on the venter, and considerable black pigmentation, in addition to brown. Nerodia erythrogaster is uniformly dark brown dorsally with a reddish or orangish venter.

Geographic Variation: There are no apparent differences in scutellation, color, or pattern between populations in southeastern Virginia (SE) and those near Hopewell and in the York-James peninsula (NW). The average number of ventrals (SE 136.0 ± 1.4, n = 54; NW 137.6 ± 2.4, n = 125), subcaudals (SE 74.7 ± 5.2, n = 50; NW 74.3 ± 5.1, n = 89), and body blotches (SE 25.4 ± 1.4, n = 54; NW 25.5 ± 1.7, n = 125) were very similar between these populations. Duellman and Schwartz (1958) reported counts of ventrals, subcaudals, and body blotches that, with one exception, were not substantially different from the Virginia data reported above. The average number of ventrals in females in southern Florida (129.2, n = 10) is lower than the average number for Virginia females (135.8 ±1.7, n = 89).

Biology: This is a highly aquatic species that is associated with large bodies of water, especially rivers, reservoirs, and marshes around bays. Nerodia taxispilota has been found in brackish and in freshwater habitats. These snakes are usually associated with open stretches of water with overhanging vegetation. They are often associated with cypress trees and stumps along the Chickahominy River (Richmond and Goin, 1938; Werler and McCallion, 1951), and with vegetation along the banks of the Appomattox River (Blem and K. Blem, 1990). Brown Watersnakes are usually diurnal, but may be nocturnal in midsummer (Blem and K. Blem, 1990). Nerodia taxispilota frequently basks on logs and overhanging vegetation during midday and in the afternoon in spring and fall, but usually only in the morning in the summer.

They are active from 4 April through 9 November, as indicated by museum records. N. D. Richmond (pers. comm.) observed them in all months of the year in New Kent County. Blem and L. Blem (1990) reported an activity period of 11 April-26 October in Chesterfield County. Blem and K. Blem (1990) reported an average body temperature of 24.8°C for snakes caught in the field and 28.2°C for snakes tested for thermal preference in the laboratory.

This snake is a predator of fish, primarily the channel catfish (Ictalurus punctatus). Richmond (1944) described the consumption of large catfish in New Kent County by this snake. The fish is captured in shallow water, usually at midbody, and taken to shore. The snake either emerges completely or stops at the water line. Despite the flopping action of the fish, the snake maneuvers its mouth toward the head of the fish, avoiding the spines. Once the fish's head is reached, the snake alternates left and right halves of the upper and lower jaws to get the widest part of the head fully in its mouth. "After the widest part of the fish's head had passed, however, the snake literally crawled outside the fish. The jaws gripped the fish tightly and its body was drawn up over the fish in a series of folds, then the jaws relaxed and the head and anterior portion of the snake slid forward, engulfing about half an inch at a time" (Richmond, 1944). In this manner, the spines, which could penetrate the snake's body, are folded down and rendered harmless. Richmond (1944) mentioned that live catfish are caught and eaten rather than dead ones. Blem and L. Blem (1990) thought the fish eaten by snakes in the Chesterfield County population were scavenged.

Adults have few predators because of their large body size. Large numbers are killed by humans. In the Appomattox River population studied by White et al. (1982), partial tails occurred in 21.4% of the male sample and 22.2% of the female sample, and the frequency of tail breakage increased with body size. They speculated that Snapping Turtles (Chelydra serpentina) biting the snakes' tails as they dangled in the water while basking, coupled with the snake's behavior of twisting vigorously when caught, was the cause of the high frequencies. Actual predators of juveniles are unknown, but Linzey and Clifford (1981) suggested raccoons (Procyon lotor), minks (Mustek vison), herons (Egretta, Butorides), and Eastern Kingsnakes (Lampropeltis getula). Nerodia taxispilota is viviparous and bears living young. The following is drawn from the studies of White et al. (1982) and Mitchell and Zug (1984) on the population near Colonial Heights and Hopewell. Size at maturity was 700 mm SVL for females and 460 mm SVL for males. Mating apparently occurred in spring. Yolking of follicles was rapid in spring and ovulation occurred in late June. Number of yolking follicles or embryos per litter was 19-63 (ave. = 33.9 ± 12.2, n = 23); however, the number of full-term embryos was 19-41 (ave. = 28.0 ± 10.6, n = 5). There was a positive correlation between litter size and female size; larger females bore larger litters. Birth occurred in late August to mid-September. Blem and L. Blem (1990) reported an average date of 2 September. This can be an abundant snake where it occurs, but no studies of the population ecology of this species have been published.

Nerodia taxispilota usually bites when caught, and a large one can inflict a nasty wound from its long teeth. They also squirt musk from glands at the base of the tail and sometimes defecate.

Remarks: Other common names in Virginia are water pilot (Carroll, 1950), and water moccasin and water rattle (Linzey and Clifford, 1981). The name "water rattle" stems from folklore that says this snake is a type of aquatic rattlesnake, and the name "water pilot" is from the myth that this snake leads other snakes to safety (Linzey and Clifford, 1981). It may be called the "water moccasin" in the Dismal Swamp area (Brothers, 1992).

Conservation and Management: This snake was once abundant in various parts of its Virginia range. Two threats to local populations are causing declines of this species in Virginia. Environmental pollution affecting fish populations can indirectly affect Nerodia taxispilota populations. Some people find that floating down rivers and shooting water snakes from the overhanging vegetation is "sport." Such misguided actions are detrimental to the continued existence of these natural predators in some areas. The status of this species needs review, especially in urban populations and isolated locations, such as at the mouth of the Appomattox River and in the Newport News Reservoir.

Brown Watersnake (Nerodia taxispilota) U.S. Range