Southern watersnake (Nerodia fasciata)

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Southern watersnake basking on a rock
IUCN Red List species status – Least Concern LEAST
CONCERN

Top facts

  • As its name suggests, the southern watersnake is a strong swimmer, and this species can remain underwater for up to 24 minutes.
  • The southern watersnake gets its scientific species name, fasciata, from the Latin word for ‘band’, which refers to the characteristic cross-band pattern on its back.
  • When feeding on fish, the southern watersnake swallows its prey head-first, but when eating frogs it consumes them rear-first.
  • Female southern watersnakes give birth to live young, and can produce up to 57 young per litter.
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Southern watersnake fact file

Southern watersnake description

KingdomAnimalia
PhylumChordata
ClassReptilia
OrderSquamata
FamilyNatricidae
GenusNerodia (1)

The southern watersnake (Nerodia fasciata) is a relatively large, heavy-bodied snake (3) which gets its scientific name from the characteristic cross-bands which mark its upper surface (2) (3), with fasciata being derived from the Latin for ‘band’ (2). Interestingly, this species is the only watersnake to have such markings (4).

Typically wider on the back than along the sides (3) (5), the cross-bands are present along the entire length of the body (2), which is covered in strongly keeled scales (3) (5). The markings can be dark brown, reddish-brown, olive or black in colour, and are separated by narrow, yellowish (2) (5), grey or reddish interspaces (2), with the contrast between the two colours being much more vivid in younger snakes (5) (6). In older snakes, this contrast can be so faint that the individual appears to be an almost uniform dark brown (2) (7).

The southern watersnake has a tan or yellow belly (3) (5) marked with large, dark spots which are rectangular, triangular or square in shape (2) (3) (5) (7). The head is distinctly wider than the neck, typically being darker on the top and lighter on the sides (5), where a dark cheek stripe runs from each eye through to the end of the mouthline (2) (5).

The southern watersnake is a sexually dimorphic species, with females typically being much longer than males (2) (3) (4), although males have proportionally longer tails (2). There are three subspecies of southern watersnake: Nerodia fasciata fasciata, Nerodia fasciata confluens and Nerodia fasciata pictiventris (2) (7), which differ primarily in geographic distribution and colour pattern (2). Even within populations of the same subspecies there is extensive variation in the colour of individuals (3) (5).

Also known as
banded watersnake, broad-banded watersnake, Cope’s water snake, Florida banded water snake, Florida watersnake, southeastern banded water snake, southern banded water snake, southern banded watersnake, southern water snake.
Synonyms
Coluber fasciatus, Natrix fasciata, Nerodia sipedon, Tropidonotus bisectus, Tropidonotus fasciatus, Tropidonotus pogonias.
Size
Average female snout-vent length: 63.8 cm (2)
Maximum female snout-vent length: 98 cm (2)
Average male snout-vent length: 53.5 cm (2)
Maximum male snout-vent length: 73 cm (2)
Average female weight: 247 g (2)
Maximum female weight: 990 g (2)
Average male weight: 114 g (2)
Maximum male weight: 270 g (2)
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Southern watersnake biology

As its name might suggest, the southern watersnake is a strong swimmer, spending about 60 percent of its time in water. This species has been recorded remaining submerged for up to an impressive 24 minutes (5).

In the more southerly parts of its range, the southern watersnake may be active year-round (2) (6), but in other areas it becomes inactive during cold winters (2) (5). From about December, spells of cold weather cause this species to retire to a warmer refuge for hibernation, typically under a pile of vegetation near water or in the burrows of other animals (5) (6).

The southern watersnake is known to be both diurnal and nocturnal, often being most active at night during the summer when the intense heat becomes intolerable (3) (5) (6). If disturbed, this species’ first reaction is to take refuge in water (2) (5), but if it cannot escape, the southern watersnake may flatten its head and body on the ground to appear larger and perhaps mimic the venomous cottonmouth (Agkistrodon piscivorus) (5). Should the threat persist, the southern watersnake may strike ferociously and repeatedly (5), and if picked up or stepped on will emit a foul-smelling musk from scent glands at the base of its tail to deter its attacker (2) (3) (5).

The southern watersnake feeds on amphibians and fish (2) (4) (5), including eels, minnows and pikes (2), as well as the occasional crayfish (2) (5). While fish tend to be the preferred prey throughout most of this species’ range (2) (4) (5), it has been discovered that frogs make up the majority of its diet in Florida (5). The non-venomous southern watersnake (8) is an active forager (5) (6), flushing its prey out of hiding by poking its head into piles of debris and aquatic vegetation before quickly pursuing its quarry and swallowing it whole (5). Interestingly, fish prey is usually eaten head-first, whereas frogs are consumed rear-first (6).

Little is known about reproduction in the southern watersnake, although male courtship aggregations have been observed in spring in shallow-water habitats, presumably to mate with receptive females (2) (6). It is thought that several males may attempt to mate with a single female (2).

The southern watersnake is a viviparous species, meaning that the female gives birth to live young which develop inside its body (7). The timing of both courtship and the birth of the young depends somewhat on the subspecies and geographic location, but this species is typically thought to mate in the spring (4) (5). Young southern watersnakes are usually born between July and October (2) (5), although the Florida banded watersnake (N. f. pictiventris) is thought to give birth between May and August (5). Litters of up to 57 young have been recorded in this species, but generally fewer are born, with an average of between 20 and 25 per litter (2) (5).  There is no evidence to suggest that female southern watersnakes produce more than one litter per breeding season (2).

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Southern watersnake range

The southern watersnake is endemic to the southern United States (1), where it can be found across the Coastal Plain of North Carolina, South Carolina and Georgia and throughout Florida (1) (2) (6) (7). The range of this species extends westwards across the southern regions of Alabama and Mississippi (2) (6) (7), and into Louisiana, Arkansas and the south-eastern parts of Oklahoma (2) (6) (7). The southern watersnake occurs as far north as south-eastern Missouri and Illinois (1) (2) (7).

This species is also found in Texas and California (1) (2) (7), where it was introduced and has since become established (1).

The three subspecies of southern watersnake all have different geographic distributions within this species’ range (7).

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Southern watersnake habitat

The southern watersnake is considered to be a habitat generalist (2), and can be found in a range of quiet, shallow aquatic habitats, including lakes, ponds, reservoirs, drainage ditches, swamps, marshes and bayous (2) (3) (5). In addition, this species has been known to occupy rice fields and slow-moving streams. The southern watersnake tends to prefer areas where the shoreline is bordered by woodland or other vegetation (5).

Interestingly, the southern watersnake is at least partially coastal, inhabiting prairie marshland near brackish water (5) (7), although due to its need for access to freshwater for drinking, this species cannot live permanently in a saltwater environment (5).

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Southern watersnake status

The southern watersnake is classified as Least Concern (LC) on the IUCN Red List (1).

IUCN Red List species status – Least Concern

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Southern watersnake threats

There are no known major threats to the southern watersnake at present, and this species is not currently considered to be at risk of extinction (4). However, in addition to being accidentally hit by vehicles on roads (3), the southern watersnake is considered to be a pest in certain parts of its range, and is often killed (4).

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Southern watersnake conservation

The southern watersnake is a widespread species with a presumed large population (1), and as a result there are currently no known conservation measures in place for this reptile. 

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Find out more

Find out more about reptile conservation:

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Authentication

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:
arkive@wildscreen.org.uk

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Glossary

Brackish
Slightly salty water, usually a mixture of salt and freshwater, such as that found in estuaries.
Diurnal
Active during the day.
Endemic
A species or taxonomic group that is only found in one particular country or geographic area.
Gland
An organ that makes and secretes substances used by the body.
Hibernation
A winter survival strategy in which the animal passes the winter in a resting state. This period of inactivity is characterised by specific biological and biochemical changes including lowered blood pressure and respiration rate. In reptiles, this is also known as brumation.
Keel
A projecting ridge along a flat or curved surface, particularly down the middle.
Nocturnal
Active at night.
Prairie
An extensive area of flat or rolling, predominantly treeless grassland, especially the large tract or plain of central North America.
Sexual dimorphism
When males and females of the same species differ in appearance.
Subspecies
A population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.
Viviparous
Giving birth to live offspring that develop inside the mother’s body.
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References

  1. IUCN Red List (January, 2014)
    http://www.iucnredlist.org/
  2. Gibbons, J.W. and Dorcas, M.E. (2004) North American Watersnakes: A Natural History. University of Oklahoma Press, Norman, Oklahoma.
  3. Palmer, W.M. (1995) Reptiles of North Carolina. University of North Carolina Press, Chapel Hill, North Carolina.
  4. Trauth, S.E., Robison, H.W. and Plummer, M.V. (2004) The Amphibians and Reptiles of Arkansas. University of Arkansas Press, Fayetteville, Arkansas.
  5. Werler, J.E. and Dixon, J.R. (2000) Texas Snakes: Identification, Distribution, and Natural History. University of Texas Press, Austin, Texas.
  6. Gibbons, J.W. and Dorcas, M.E. (2005) Snakes of the Southeast. University of Georgia Press, Athens, Georgia.
  7. The Reptile Database - Nerodia fasciata (January, 2014)
    http://reptile-database.reptarium.cz/
  8. MobileReference (2009) The Illustrated Encyclopedia of North American Reptiles and Amphibians: An Essential Guide to Reptiles and Amphibians of USA, Canada, and Mexico. MobileReference, Boston.
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Image credit

Southern watersnake basking on a rock  
Southern watersnake basking on a rock

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