Northern Water Snake

Northern Water Snake2 White Oak Canyon 160824
White Oak Canyon Trail in Shenandoah National Park adjacent to boggy, wet area. The banding and colors of this snake are either a northern water snake or a copperhead, a fully grown adult about 3-4 feet long (maximum size for either species). 

Common Name: Northern Water Snake, common water snake, banded water snake, dryland moccasin, water moccasin, water adder, water viper – Among the various snakes that are primarily aquatic, this species is the most common in the northeastern and mid-Atlantic states.

Scientific Name: Nerodia sipedon – Several references attribute the genus name to the Greek word for flowing, neros. This cannot be correct since the Greek word for flowing is ρεύση pronounced “refsi.”  The more likely etymology is the Greek god of the sea Nereus from which neritic, an adjective for shallow water, is derived. It is a shallow water snake. The species name is also obscure. Some references again cite the Greek sepedon, a “snake whose bite causes mortification,” which would be an adder or a viper but water snakes are not poisonous. The Latin word for snake, serpens, is more likely. Natrix is the original generic name occasionally in use.

Potpourri: The undulating black stripes that separate the alternating patches of tan and brown of the northern water snake appear distorted as if viewed in refraction beneath the rippled pond surface of its habitat. The chiaroscuro effect is camouflage, allowing a stealthy approach to unwitting prey and protection from witting predators. Intraspecies color variability is substantial with red tones ranging to roan and different shades of gray. Brightness and clarity are accentuated in new skin emerging after a molt which gradually fades until only nuances of earth tones remain as the skin ages. Older snakes are dark brown to nearly black. It is called water snake for a reason―it is a reptilian hunter of smaller aquatic species including fish and amphibians in small ponds and along streams where its quarry abound. The combination of inconsistency in color and frequent terrestrial excursions to and from aquatic hunting grounds results in frequent misidentification as a water moccasin (Agkistrodon piscivorus), which, as the species name indicates, is also a fish (piscis) eater (vorare).

Fear of snakes or ophidiophobia is one of the most common forms of zoophobia. This is almost certainly a result of evolutionary behavior buried deep in the amygdala of every primate for whom snakes comprise a real and present danger … a propensity retained in Homo sapiens. Genesis makes it clear from the Bible’s outset that the serpent of Eden is the fount of all evil. The sight of a snake evokes both fright and flight in the sympathetic nervous system which overrides rational pre-frontal cortex thinking―water snake becoming water viper.  The water moccasin is one of the three pit vipers in the Mid-Atlantic region that is poisonous and necessarily avoided; the other two are the copperhead (A. contortrix) and the timber rattlesnake (Crotalus horridus). All three have circumferential bands of a variety of brownish hues similar to those of the northern water snake. [1] Cursory inspection would reveal that water moccasins have larger, block-shaped heads with a narrower neck and thick bodies, where other water snakes are thin and narrow on both counts.[2] However, when faced with a snake near water, it takes a great deal of poise to make a rational determination … and snakes are not patient. The only fully reliable identification is the white mouth lining from which the name cottonmouth derives, but by then it might be too late.  Keeping at a safe distance from any snake encountered in the wild is the best policy, as many, including the northern water snake, are quite aggressive if cornered and they all can and will bite.

While northern water snakes are killed relatively frequently due to either mistaken identity or general ophidiophobia, they are not endangered. They are an exceptionally successful species that is, if anything, too prolific. There are a number of reasons for this, but surely one of the most important is their domination of the freshwater habitat, where food is abundant and competition, at least for snakes, is limited. The ancestors of the 3400 living snakes that comprise the suborder Serpentes first appear in the fossil record in the early Cretaceous Period about 100 million years ago (mya) as terrestrial vertebrate predators. It is postulated that they were primarily nocturnal hunters that sought out small animals with soft bodies in vegetative habitats, the proverbial snake in the grass. Like the mammals, snakes were ideally positioned to radiate outward across all continents after the Cretaceous-Paleogene extinction of 66 mya wiped out the dominant dinosaurs.  Competition led to evolutionary pressures to kill more effectively with constriction or poison, for articulated jaws to increase portion size, and to seek new habitats for exploitation while maintaining the basic streamlined body shape.[3] Riparian water snakes and saltwater sea snakes took up swimming and diving in the three dimensional aquatic environment for subsistence.

Northern Water Snake 2 Big Run 130810R
The Northern Watersnake hunts for prey with its head just above water.

The ponds and streams of farm country and the water hazards of golf courses offer a smorgasbord for the night-stalking northern water snake. They are easy to spot in the dusky twilight as they course about with their heads above water like “Nessie” in search of likely prey.  An absolute affirmation of food choices was established by a somewhat controversial yet incontrovertible field study conducted in the George Washington National Forest in 1939. Thirty northern water snakes were dissected to determine that their diet consisted of 48% non-game fish, 19% frogs, 13% game fish, 13% salamanders and 3% toads with the balance indeterminate or minimal. [4] And, surprisingly, they do this without a great deal of effort. Fifty snakes were outfitted with radio tracking devices and monitored over a three year period to determine that they spent between 1.43% and 2.38% of their time foraging, which works out to about thirty minutes a day. [5] That they are terrestrial animals that go fishing is also evident in the manner of consumption. The fish is typically dragged out of the water and subdued on land where the tables are turned. [6] Since water snakes don’t spend much time hunting, there is a lot of time for other activities, among them procreation.

Squamate reptiles, which includes snakes, lizards, and a smaller group called amphisbaenians or worm lizards, have two penises called hemipenes.  There is also some evidence of a duality in the female organs of some species called hemiclitores. [7] The evolution of sexuality of one form or another in most living things is testimony to the efficacy of random genomic mixing in perpetuating a species. Environmental variations of the geologic time frame of moving tectonic plates, orogenic mountains, and subducting seas are the forcing functions of survival of the fittest. A means to implant sperm directly into a protected repository for fertilization of the egg only became necessary when animals came ashore … fish do not have penises since semen mobility is not diminished in aquatic environs. The current consensus is that what began as a genital bud about 300 mya adapted according to usage and effectiveness. Placental mammals, turtles, and crocodiles have a single penis while almost all birds, ducks being one exception, have none. As evidence of the random mutation nature of sexuality, female marsupial mammals have two wombs and three vaginas and males have branched, two-headed penises. [8] Whatever works.

Snake sex is accomplished one penis at a time, each connected to a separate and independent testicle―a double-barreled shotgun. This almost certainly is related to the role of mate choice, the behaviors that lead to successful sex to create the progeny that set the genetic heritage of the species.  Both sexes have a role to play in this the most important of biological functions. Female snakes can store sperm for up to five years, releasing it for impregnation only when they choose to do so based on criteria that are at best obscure, but which must surely have something to do with viability of offspring (or why bother?). Male snakes advance their genetic potential by having sex with as many females as possible (nothing new here). The dual phallus arrangement allows for some flexibility in intercourse so that a fully charged testicle is always at the ready. Testing has been done with lizards who share the hemipenes anatomical feature to confirm that penis use is alternated and that a second use of the same organ results in a diminution of sperm quality and quantity (determined experimentally by taping one side shut). [9] The importance of sexual selection to speciation has motivated extensive theoretical research, mostly speculative. Four basic theories have emerged with the alliterative titles sexy sons, good genes, sperm competition and sexual conflict. The first two are related and imply a preference for “maleness” in appearance or behavior and sperm competition speaks for itself, a race to the finish. In the snake world, it is more likely sexual conflict that dominates so that two penises are better than one for the male and multiple choice is better for the female. [10] However, this matter is far from settled. Male northern water snakes are smaller than females (sexual dimorphism) but their size does not correlate to mating success, suggesting that sperm competition is the key factor. [11], [12] One thing is certain. Sex is a strong instinctual drive that operates outside cognition.

Northern Water Snake Molting Hazel River 180526
The opaque eyes and dull skin are indicative of imminent molting.

Regardless of the how’s and why’s of snake sex, the consequence is the birth of about thirty live, wriggling snakelets usually on land near water. While they are left to their own devices with no parental guidance, they forego the more typical reptilian egg stage and are thus not subject to being eaten while sessile and incubated. The young of any species are subject to predation according to size … juvenile northern water snakes are eaten by many predators, notably king snakes and raccoons on land and large-mouth bass and snapping turtles in the water. Those that survive for a few weeks grow out of their skin and need to molt, shedding the skin from the tip of the nose to the tail in one continuous unbroken sheath. During the first year, rapid growth necessitates molting every other month which segues to annually for adults. The molting process occurs from the inside out, with a new layer of skin growing underneath the old. This includes the eyes, which become opaque and nearly sightless for several days as the new layer forms. The essentially incapacitated snake holes up in a secluded and quiescent lair to await clairvoyance. [13] With a glowing new coat, the rejuvenated adult snake sets out on its natural duty to find a mate. Field experimentation has shown that female northern water snakes are five times more likely to be located by a male after shedding. [14] And thus another thirty snakes start anew in a geometrical progression.

Northern water snakes are quite common and can become a nuisance species when introduced to non-native environments. The serpentine combination of crypsis and lethality is well-suited to finding prey in a new area while avoiding the retribution of local predators. The brown tree snake was accidentally transported from its home range in the South Pacific to the island of Guam where it extirpated most of the local bird population; Hawaii has been on guarded alert for over fifty years to prevent its intrusion there. Closer to home, pet Burmese pythons escaped into the Florida Everglades … the furry mammal population, including pet dogs and cats, are now at risk. While water snakes do not eat birds or beasts, they are consummate aquatic hunters. The wetlands of California’s Central Valley are gradually becoming infested with northern water snakes that have been accidentally introduced there, probably as escaped pets. A recent field survey of a two hectare watershed near Roseville, California estimated the density of the invasive watersnake at 56.2 per hectare (more than 20 per acre). [15] Sometimes a snake in the water can be worse than a snake in the grass.

References:

  1. Behler, J. National Audubon Society Field Guide to Reptiles and Amphibians, Alfred A. Knopf, New York, 1979, pp 637-639, 682-689.
  2. Johnson, S. University of Florida Department of Wildlife Ecology and Conservation at https://ufwildlife.ifas.ufl.edu/water_moccasin_watersnake_comparison.shtml
  3. Hsiang, A. et al “The origin of snakes: Revealing the ecology, behavior, and evolutionary history of early snakes using genomics, phenomics, and the fossil record”. BMC Evolutionary Biology. 20 May 2015 Volume 15. https://bmcevolbiol.biomedcentral.com/articles/10.1186/s12862-015-0358-5
  4. Linzey, D. and Clifford, M. Snakes of Virginia, University Press of Virginia, Charlottesville, Virginia, 1981. pp 44-48, 123-138.
  5. Cundall, D. et al. “Foraging Time Investment in an Urban Population of Watersnakes (Nerodia sipedon)” Journal of Herpetology, 1 June 2011. Volume 45(2) pp 174-177.
  6. Sutton, W. et al. Nerodia sipedon (northern water snake) feeding behavior. Herpetological Review 2013 Volume 44 (2) p 333.
  7. Gredler, M.et al. “Development of the Cloaca, Hemipenes, and Hemiclitores in the Green Anole, Anolis carolinensis”. Sexual Development January 2015 Volume 9 (1) pp 21–33.
  8. Drew, L. I, Mammal, Bloomsbury Sigma Publishing, London, 2017, pp 84-87, 99-104.
  9. http://snakesarelong.blogspot.com/2014/03/why-do-snakes-have-two-penises.html?
  10. Hosken, D. and Stockley, P. “Sexual selection and genital evolution” (PDF). Trends in Ecology and Evolution. 2 February 2004. Volume19 (2) pp 87–93. Available at:11. Weatherhead, P. et al. “Sex ratios, mating behavior and sexual size dimorphism of the common water snake, Nerodia sipedon “. Behavioral Ecology and Sociobiology. May 1995 36 (5) pp 301–311
  11. Schulte-Hostedde A. et al. “Intraspecific variation in ejaculate traits of the northern watersnake (Nerodia sipedon)”. Journal of Zoology. 24 May 2006 Volume 270 (1): 147–152.
  12. http://www.virginiaherpetologicalsociety.com/reptiles/snakes/northern-watersnake/northern_watersnake.php
  13. Jellen, B. and Aldridge, R. “It takes two to tango: Female movement facilitates male mate location in wild common water snakes (Nerodia sipedon)”. Behaviour. 1 January 2014 Volume 151 (4) pp 421–434.
  14. Rose, J. et al. “Trapping Efficiency, Demography, and Density of an Introduced population of Northern Watersnakes, Nerodia sipedon, in California” Journal of Herpetology. Volume 47 (3) pp 421–427.