Basics of Snake Fangs

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Solenoglyphous fangs of a Gaboon Viper

Snake fangs are specialized, elegantly modified teeth. Some are like hypodermic needles, others are more like water slides. But all serve essentially the same purpose: to inject venom into the snake's prey. Occasionally, the fangs are also used in defense, but studies show that snakes striking in defense are far less likely to inject venom than when they're striking at a prey item, a fact that has assuaged the fears of many an ophidiophobic. I wanted to write a brief review of snake fang types, because their anatomy is very interesting and also because of their important role in classifying snakes and understanding how different groups of snakes are related to each other.

Cross-sections of fangs:
F is an aglyphous tooth.
G is an opisthoglyphous fang.
H is a proteroglyphous fang.
I is a hollow solenoglyphous fang.
From Bauchot (2006)

Many snakes produce venom, which is essentially very strong saliva, in glands in their heads (which is where you produce your saliva, too). We call these glands venom glands if they are well-developed, complete with an interior cavity, a duct connecting to a hollow fang, and compressor muscles that generate high pressures when the jaws are rapidly closed. If they lack these features, we usually call them Duvernoy's glands instead. Because there is a lot of variation among snake species in the structure of these glands and their associated teeth, there is some debate about whether or not venom glands and Duvernoy's glands are really two forms of the same thing. Either way, three groups of snakes (atractaspidines, elapids, and viperids) have independently evolved an advanced apparatus to deliver large quantities of venom during a brief strike, and many other snakes (and a few lizards) have evolved less sophisticated, but still relatively effective, modifications to their teeth in order to deliver venom after they have grabbed their prey and are "chewing" on it. The teeth of modern snakes are classically divided into four types, three of which are typically called fangs. The four tooth types have fancy names, all of which involve the Greek word glyph, one of the meanings of which is "groove". They are as follows:

Solenoglyphous

Folding of solenoglyphous fangs.
Fang is in red, maxilla green,
prefrontal orange, pterygoid yellow,
ectopterygoid purple. Vipers lack
premaxillary and palatine teeth.
From Bauchot (2006)

This most sophisticated fang type evolved once, in the ancestor to all modern vipers, which lived in Asia about 40 million years ago. Fossils suggest that solenoglyphous fangs have changed little since that time, even though vipers have undergone an incredibly successful radiation into 320 extant species found on all continents except for Australia and Antarctica. Solenoglyphous fangs are long and tubular and are attached to the snake's maxillary bone. Most snakes have several tooth-bearing bones, including four (the premaxilla, maxilla, pterygoid, and palatine) in the upper jaw, and one (the dentary) in the lower. In humans, three of these bones (the premaxilla, maxilla, and dentary) also bear teeth - your premaxilla holds your top incisors, while your maxilla holds your upper canines and molars and your dentary all your lower teeth - while the others form part of the roof of the mouth. In vipers, the maxilla bears only a single tooth (the fang) and is hinged so that the fangs can be folded back parallel to the jaws when the mouth is closed, or erected perpendicular to the jaws, the position when striking. The teeth in the pterygoids and dentaries work together to manipulate food once it gets into the mouth. Solenoglyphous fangs are strikingly similar to hypodermic needles. They have a hollow core that receives venom from the venom gland at the entrance orifice near the base and injects it from a slit-like exit orifice on the front of the fang near the tip. If the opening were at the very tip of the fang, its strength would be compromised and it would lack the sharp point needed to penetrate the target. Even under normal use, vipers shed their fangs every two months.

Modified solenoglyphous fang of
African Burrowing Asp (Atractaspis engaddensis)

A similar fang type evolved a second time about 29 million years ago in a group of African snakes, currently placed in the family Lamprophiidae, subfamily Atractaspidinae. Two genera, Atractaspis (mole vipers, burrowing asps, or stiletto snakes) and Homoroselaps (African dwarf garter or harlequin snakes), possess elongate anterior fangs, although only those of the stiletto snakes are movable. Stiletto snake fangs pivot on a socket-like joint that is more flexible than those of vipers, allowing these snakes to strike beside and behind them with their mouth closed. This is an adaptation to living underground and envenomating small mammals and other reptiles in narrow subterranean burrows. The fang morphology of atractaspidines and viperids is remarkably similar, considering that these two snake lineages last shared a common ancestor over 40 million years ago.

Proteroglyphous

Proteroglyphous fangs of an Eastern Green Mamba
(Dendroaspis angusticeps). Don't try this.
From Bauchot (2006)

This fang type also evolved only once, in the ancestor to all modern elapids, which lived 25-40 mya in Asia or Africa. Proteroglyphous fangs are in the front of the mouth and are about three times shorter than solenoglyphous fangs. This is because they are not hinged. Snakes with proteroglyphous fangs typically strike their prey and hang on until the venom has taken effect, as opposed to releasing they prey and then tracking it down. Some elapids constrict their prey at the same time as envenomating it. Over 350 species of elapids exist today, including well-known groups such as cobras, mambas, death adders, taipans, coralsnakes, and sea snakes, and less-well-known species, mainly found in Australia, of which a good number are small, secretive, and not considered dangerous to humans.

Maxilla of a proteroglyphous snake showing the almost
completely closed groove along the anterior edge connecting
the two orifices, as well as the aglyphous tooth at the
rear of the maxilla. This line may be obscured in longer fangs.
From Shea et al. 1993

Unlike solenoglyphs, some proteroglyphs have other teeth on the maxilla behind the fang. However, the fang is always separated from the other teeth by a gap, called a diastema. Some elapids have more than one functional fang on each side. In both vipers and elapids, there are usually at least two fangs on each maxilla at any one time, one that is in use and one that is a reserve fang. Both fangs are draped in a layer of connective tissue and skin called the fang sheath. Some proteroglyphs have partially movable fangs, including many of the most dangerous species such as mambas, taipans, and death adders. A few, such as spitting cobras, have modified exit orifices to their fangs that are smaller and rounder than in other cobras, a modification that increases the velocity with which venom is ejected. Modifications to the muscles and the fang sheath also facilitate spitting in these cobras. A few elapids, such as sea snakes that eat only fish eggs, have lost their fangs and their venom glands, which suggests that the primary role of venom, at least among elapids, is in feeding rather than in defense.

Opisthoglyphous

Opisthoglyphous fang of Eastern Hog-nosed Snake

These are commonly known as "rear-fanged" snakes. Opisthoglyphous fangs are grooved rather than hollow and are found near the back of the maxilla, behind the normal teeth. Typically, snakes with rear fangs must chew on their prey to bring their fangs into a biting position. There is considerable variation in the size, shape, and number of opisthoglyphous fangs from species to species, and sometimes even within a species. Most opisthoglyphous fangs are connected to Duvernoy's glands, which differ from true venom glands in several important ways, most notably in that they lack associated muscles to generate the pressure needed to evacuate venom, as in solenoglyphous and proteroglyphous snakes. The pressure on the venom glands of biting solenoglyphs and proteroglyphs can exceed 30 psi, the pressure of a car tire, whereas the pressure inside the Duvernoy's glands of opisthoglyphs is generally less than 5 psi. Because Duvernoy's glands also lack a chamber for storing venom, the idea is emerging that opisthoglyphous snakes probably secrete their venom only during chewing, which explains why prolonged bites by opisthoglyphs generally have more severe effects.

Opisthoglyphous fangs of Boomslang (Dispholidus typus)
Don't do this either.

Most of these snakes are not harmful to humans, with a few notable exceptions. Boomslangs and Twigsnakes are arboreal, diurnal African colubrines that prey on lizards and birds. They have short heads, rear fangs situated comparatively close to the front of the mouth, and partially muscled Duvernoy's glands. They also have potent venoms and their bites have killed several people, including two prominent snake biologists, Karl Schmidt and Robert Mertens. Bites from other rear-fanged snakes are known to cause relatively mild, transient, and local symptoms, but clinical documentation of these bites and their effects is scattered, incomplete, and frequently anecdotal. Many are written by the victim themselves! The above notwithstanding, bites from opisthoglyphs are generally less medically important than those from proteroglyphs and solenoglyphs. As a result, snake venom research has not focused on them, so there is still much that we do not know about this group of snakes, some of which are becoming increasingly common in the pet trade. Based on what little we do know, the composition of opisthoglyph venom/Duvernoy's secretion is fairly similar to that of viperids, elapids and atractaspidines, which makes sense given that each of these groups is more closely related to certain opisthoglyphs than they are to one another.

A: python, B: viper, C: rear-fanged colubroid, D: cobra
The f  marks the portion of the maxilla where the fang develops.
E shows the elongation of the posterior part of the
maxilla pushing forward the developing fang of a
night adder (d.a.o. = days after oviposition)
From Vonk et al. 2008

Unlike the first two groups, opisthoglyphous fangs appear to have evolved more than once, in snakes as diverse as Quill-snouted Snakes, Neck-banded Snakes, and Boomslangs. At least, that's what we used to think. Actually, it is likely that both solenoglyphous and proteroglyphous fangs evolved from opisthoglyphous fangs, as revealed by an ingenious study that used evidence from embryology and genetics to reveal the evolutionary origins of the three types of snake fangs. In a snake embryo, tubular fangs are formed by the infolding of ridges on the front and back sides of the fang, such as those that form the groove of opisthoglyphous fangs. Furthermore, front fangs develop from the rear part of the upper jaw, and are strikingly similar in their formation to rear fangs. They are pushed into the front of the mouth by disproportionate growth of the initially small part of the maxilla that is behind them. Finally, in the anterior part of the maxilla of front-fanged snakes, expression of a gene called sonic hedgehog, which is responsible among other things for the formation of teeth, is suppressed.

Relative size of the venom gland (VG) in
A: rear-fanged colubrid (Helicops leopardinus),
B: boomslang, C: homalopsid,
D: cornsnake, E: African egg-eater
SG = supralabial salivary gland
From Fry et al. 2008

Although developmental similarity is not conclusive proof of structural homology (similarity due to inheritance rather than due to other factors), these findings are consistent with the hypothesis that solenoglyphous, proteroglyphous, and at least some opisthoglyphous fangs are homologous structures. The hypothetical evolutionary trajectory was thus: some snakes evolved grooved fangs in the rear of their mouth. In a few cases (viperids, elapids, and atractaspidines), they subsequently lost the preceding teeth as what was formerly a rear fang became a tubular front fang. Other snakes retained their anterior teeth (at least some non-front-fanged colubroids), and still others developed fangs but then lost them (aglyphs such as ratsnakes). Evidence for this surprising final part comes from the formation of the maxilla and its teeth, which takes place in a single piece in pythons, but from two pieces in all fanged snakes as well as in ratsnakes, a pattern which supports a single evolutionary origin and subsequent loss of fangs. Additionally, vestigial Duvernoy's glands have been found in ratsnakes, egg-eaters, pareatid slug-eaters, and other nonvenomous aglyphs, a discovery that has led to the misleading generalization that all snakes are venomous and much subsequent misunderstanding among the non-scientific community. Toxic saliva does not a venomous animal make, as evidenced by the fact that even human saliva injected subcutaneously will produce pain and swelling.

Aglyphous

Both boas and pythons have only
aglyphous teeth, which is about
the only thing this film got right.

This word is used to describe unmodified teeth, essentially non-fangs. All snakes, even those that possess fangs of the first three types, have aglyphous teeth which they use for gripping their prey as they manipulate it during swallowing. As I just mentioned, many advanced snakes that today have only aglyphous teeth probably evolved from fanged ancestors. Several of these snakes, such as North American kingsnakes, ratsnakes, and bullsnakes, have atrophied Duvernoy's glands that lack toxin-producing serous cells. These snakes employ other sophisticated techniques, such as constriction, which is also used by more primitive snakes like boas and pythons (which did not evolve from fanged ancestors).

There are very few dangerous species of aglyphs, but one, Rhabdophis tigrinus, is becoming well-known as one of the only snakes capable of sequestering toxins from its prey for use in its own defense. This species has enlarged posterior maxillary teeth that lack grooves, so they are by definition aglyphous. However, it has relatively potent venom and has caused the deaths of several people. Among colubroids, the distinction between opisthoglyphs and aglyphs has never been entirely clear, but I'm distinguishing between them here because they are two of the four traditionally recognized types of snake teeth. Although the four types of snake teeth in this article are commonly discussed, a more accurate classification for snake teeth might be to divide them into tubular (the fangs of viperids, elapids, and atractaspidines), grooved (the rear fangs of non-front-fanged colubroids), and ungrooved (all other snake teeth).

Aglyphous (ungrooved) teeth and rear fangs of
Rhabdophis tigrinus
From Mittleman & Goris 1974

Happily for snake biologists like myself, the evolution of fangs opened the door for a massive evolutionary radiation of advanced snakes (>2800 species, or >80% of all living snake species). Although sophisticated venom delivery systems, of which fangs are just one of many integral parts, were clearly evolutionary advantageous, they have obviously also been costly at times, leading to their loss in ratsnakes, egg-eaters, and other lineages of advanced snakes. Also worth noting is that many lineages of basal snakes have got along just fine without venom, so there is not an inherent superiority of being venomous as the word "advanced" seems to imply. Rather, some have suggested that during periods of transition from forest to grassland, such as that which took place simultaneous to the dramatic colubroid radiation during the Miocene, snake taxa that were characterized by slow locomotion and constriction (boas & pythons) were supplanted by those characterized by rapid locomotion (many aglyphous colubrids) or passive immobilization (tubular- and grooved-fanged vipers, elapids, and atractaspidines that could use venom to catch their prey). Of course, both slow locomotion and constriction have subsequently been re-evolved among the colubroids, but there has been a lot of time since the Miocene.

ACKNOWLEDGMENTS

Thanks to Daniel Rosenberg (boomslang fang) and Nick Kiriazis (hognose fang) for use of their photographs.

REFERENCES

Bauchot R, editor. 2006. Snakes: A Natural History. New York, New York: Sterling Publishers. <link>

Cundall, D., (2002) Envenomation strategies, head form, and feeding ecology in vipers. In: Biology of the Vipers: 149-162. G. W. Schuett, M. Höggren, M. E. Douglas & H. W. Greene (Eds.). Eagle Mountain Publishers, Eagle Mountain, UT <link>

Greene, H. W. (1997) Snakes: The Evolution of Mystery in Nature. Berkeley: University of California Press <link>

Fry BG, Scheib H, van der Weerd L, Young B, McNaughtan J, Ramjan SR, Vidal N, Poelmann RE, Norman JA, 2008. Evolution of an arsenal: structural and functional diversification of the venom system in the advanced snakes (Caenophidia). Mol Cell Proteomics 7:215-246 <link>

Hayes, W. K., S. S. Herbert, G. C. Rehling & J. F. Gennaro, (2002) Factors that influence venom expenditure in viperids and other snake species during predator and defensive contexts. In: Biology of the Vipers: 207-234. G. W. Schuett, M. Höggren, M. E. Douglas & H. W. Greene (Eds.). Eagle Mountain Publishers, Eagle Mountain, UT <link>

Jackson K, 2002. How tubular venom‐conducting fangs are formed. J Morphol 252:291-297 <link>

Kardong, K. V. & T. L. Smith, (2002) Proximate factors involved in rattlesnake predatory behavior: a review. In: Biology of the Vipers: 253-266. G. W. Schuett, M. Höggren, M. E. Douglas & H. W. Greene (Eds.). Eagle Mountain Publishers, Eagle Mountain, UT <link>

Kardong KV, 1996. Snake toxins and venoms: an evolutionary perspective. Herpetologica 52:36-46 <link>

Kuch, U., J. Müller, C. Mödden & D. Mebs (2006). Snake fangs from the Lower Miocene of Germany: evolutionary stability of perfect weapons. Naturwissenschaften 93, 84-87

LaDuc, T. J., (2002) Does a quick offense equal a quick defense? Kinematic comparisons of predatory and defensive strikes in the Western Diamond-backed Rattlesnake (Crotalus atrox). In: Biology of the Vipers: 267-278. G. W. Schuett, M. Höggren, M. E. Douglas & H. W. Greene (Eds.). Eagle Mountain Publishers, Eagle Mountain, UT <link>

Mittleman M, Goris R, 1974. Envenomation from the bite of the Japanese colubrid snake Rhabdophis tigrinus (Boie). Herpetologica 30:113-119 <link>

Pyron, R. A., F. T. Burbrink, G. R. Colli, A. N. M. de Oca, L. J. Vitt, C. A. Kuczynski & J. J. Wiens (2011). The phylogeny of advanced snakes (Colubroidea), with discovery of a new subfamily and comparison of support methods for likelihood trees. Mol. Phylogenet. Evol. 58, 329-342 <link>

Savitzky AH, 1980. The role of venom delivery strategies in snake evolution. Evolution 34:1194-1204 <link>

Shea G, Shine R, Covacevich JC, 1993. Elapidae. In: Glasby C, Ross G, Beesley P, editors. Fauna of Australia. Canberra: AGPS <link>

Vonk FJ, Admiraal JF, Jackson K, Reshef R, de Bakker MA, Vanderschoot K, van den Berge I, van Atten M, Burgerhout E, Beck A, 2008. Evolutionary origin and development of snake fangs. Nature 454:630-633 <link>

Weinstein SA, Warrell DA, White J, Keyler DE, 2011. "Venomous" Bites from Non-Venomous Snakes: A Critical Analysis of Risk and Management of "Colubrid" Snake Bites. Amsterdam: Elsevier <link>

Weinstein SA, White J, Keyler DE, Warrell DA, 2013. Non-front-fanged colubroid snakes: A current evidence-based analysis of medical significance. Toxicon. 69, 103-113 <link>

Weinstein S, White J, Westerström A, Warrell DA, 2013. Anecdote vs. substantiated fact: the problem of unverified reports in the toxinological and herpetological literature describing non-front-fanged colubroid (“colubrid”) snakebites. Herpetological Review 44:23-29.

Wüster, W., L. Peppin, C. Pook & D. Walker (2008). A nesting of vipers: Phylogeny and historical biogeography of the Viperidae (Squamata: Serpentes). Mol. Phylogenet. Evol. 49, 445-459 <link>

Young BA, Dunlap K, Koenig K, Singer M, 2004. The buccal buckle: the functional morphology of venom spitting in cobras. J Exp Biol 207:3483-3494 <link>

Life is Short, but Snakes are Long by Andrew M. Durso is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.

Dragonsnakes

This post now available in Spanish!
Este blog ya está disponible en español!

Head of Xenodermus javanicus

One of the weirdest-looking snakes in the world is Xenodermus javanicus, also called the Javan Tubercle Snake, Javan Mudsnake, Rough-backed Litter Snake, or, best of all, the Dragonsnake. Although they don't breathe fire, their anatomy is strange enough to evoke images of mythical creatures. The first Dragonsnake was described in 1836 by Danish zoologist Johannes T. Reinhardt. He named it Xenodermus, Greek for "foreign skin", because of its peculiar scales, of which Reinhardt described three types. A triple row of large keeled scales runs down the center of the back, flanked by two rows of huge keeled tubercles that resemble crests more than scales. The gaps between these knobby rows are covered in small irregular smooth diamond- and pentagon-shaped scales, whereas the space below the tubercles is coated in more traditional parallel rows of keeled dorsal scales, which nevertheless resemble a highly organized bed of oysters more than typical colubrid scalation.

Dorsal scales of Xenodermus javanicus

Given the dorsal side only, it's difficult to tell what the taxonomic relationships of Dragonsnakes are. However, you can tell this snake is a colubroid if you examine the ventral side, where wide, well-developed ventral scales are present, unlike the smaller ventral scales of more primitive snakes. The tail, which constitutes up to a third of the total length, has a single row of scales on the underside, a characteristic reminiscent of vipers but also found in some colubroids. Overall, the head is probably the weirdest attribute. The top, sides, and bottom of the head are covered by small granular scales, similar to those of pythons and other henophidians. But a few specialized scales grace the nose and lips of Dragonsnakes. These include about 20 labial scales, a small rostral scale at the tip of the nose (impossible to see from above), two large nasal scales, directed forward, enclosing the nostrils, and several small shields in the vicinity of these nasal scales, separated by bare skin. What are all these weird scales for? Why didn't Dragonsnakes evolve more specialized scales, like the other descendants of their common ancestor with colubrids? These are open questions, but the Dragonsnake's environment probably has something to do with it. Another rare Bornean reptile, the Earless Monitor Lizard (Lanthanotus borneensis), has a similar mixture of high- and low-entropy scalation.

Ventral side of Xenodermus javanicus

Dragonsnakes' closest relatives are 16 species of obscure snakes in 4 genera that together make up the family Xenodermatidae. Xenodermatids occupy a position similar to that of pareatids, near the base of the colubroid family tree. Traditionally, both xenodermatids and pareatids were considered subfamilies of the "junk family" Colubridae, but recent phylogenetic analyses all agree that they are only distantly related to other Colubridae, and must therefore be recognized as separate families. Xenodermatids are the most distantly related colubroids, or the "sister group" to all other colubroids, having diverged nearly 50 million years ago at the beginning of the Cenozoic, four times closer to the extinction of the dinosaurs than to today. Intriguingly, one recent article found strong support for a sister-group relationship between xenodermatids and the awesomely bizarre acrochordids, or filesnakes. This small family of three freshwater and marine species is found from northern Australia and the Solomon Islands west to India and Sri Lanka.

Xenodermus javanicus

Dragonsnakes are found in southeast Asia, including southern Burma and Thailand and peninsular Malaysia, as well as on the islands of Borneo, Sumatra, and Java. Although this area was once connected, the isolation of the islands and mainland has probably resulted in geographic isolation among populations of Dragonsnakes. Although no study to date has examined either morphological or genetic differences among Dragonsnakes from different islands, I wouldn't be surprised to see them split up into multiple species once this information eventually becomes available. We know a little about the ecology of Dragonsnakes in the wild. They are active at night, when they hunt for frogs along rocky streams in tropical rain forests, as well as in rice fields. They lay several clutches of 2–4 eggs each year during the rainy season, from October to February. The young hatch after an incubation period of about two months. Apparently when you grab one, it freezes, holding its body stiff, a behavior which you can see well in this video, taken by field herpers in Indonesia.

Dragonsnake plate from Dumeril's Erpetologie Generale,
showing in detail the scale anatomy.
This plate hangs on the wall in my dining room.

Apparently Dragonsnakes are increasing in popularity in the pet trade, so we may learn more about certain aspects of their biology through the keeping of captive individuals. Hopefully collection from the wild will be kept to a minimum, and somebody one day will conduct a detailed study of Dragonsnake ecology.

ACKNOWLEDGMENTS

Thanks to Tom Charlton, Mister Pupkin, and LOB for use of their photographs.

REFERENCES

de Rooij, N. (1917) The Reptiles of the Indo-Australian Archipelago. Il. Ophidia. Leiden: E. J. Brill <link>

Kopstein, F. 1938. Ein beitrag zur morphologie, biologie, und ökologie von Xenodermus javanicus Reinhardt. Bulletin of the Raffles Museum 14:168-174. <link>

Pyron RA, Burbrink F, Wiens JJ, 2013. A phylogeny and revised classification of Squamata, including 4161 species of lizards and snakes. BMC Biology 13. <link>

Reinhardt, J. T. 1836. Afhandling om Xenodermus javanicus. Oversigt over det Kongelige Danske videnskabernes selskabs forhandlinger. Kjobenhavn 3: 6-7 <link>

Life is Short, but Snakes are Long by Andrew M. Durso is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.

Pelagic Sea Snakes and the animals that live on them

Click here to read this article in Spanish!

Haga clic aquí para leer este artículo en español!

This overdue post was inspired by the symposium ‘‘New Frontiers from Marine Snakes to Marine Ecosystems’’ presented at the annual meeting of the Society for Integrative and Comparative Biology, January 3–7, 2012 at Charleston, South Carolina, and featured in a special issue of the journal of the same name.

Head of a Pelagic Sea Snake, Pelamis platura

I've written before about some of the amazing aspects of sea snake biology. From the morphological and physiological to the behavioral and reproductive, few sea snake adaptations cease to amaze. But one topic I had never before considered was marine snake parasitology. I knew that the skin of whales, the shells of sea turtles, the hulls of ships, and other mobile pelagic surfaces often serve as a substrate for smaller, more sessile marine organisms, such as barnacles, collectively known as epibionts. In fact, I recently learned that the total weight of all the barnacles on a single Gray Whale can exceed seven hundred pounds and that these barnacles serve as homes for other, more parasitic hitchhikers such as whale lice. But I had never heard of marine reptiles other than sea turtles harboring parasites.

The range of the Pelagic Sea Snake, which is
the world's widest ranging species of snake

I was surprised to learn that many marine snakes play host to epibionts. Twenty-eight of the ~65 species of sea snake have been documented to harbor at least one kind of epibiont. But one species, the Pelagic or Yellow-bellied Sea Snake (Pelamis platurus [sometimes platura]), harbors more kinds of epibionts than any other. In order to understand why, it is helpful to know that Pelamis platurus is found farther out in the open ocean than any other kind of sea snake. Most species of sea snake stick relatively close to reefs and shores in the Indian and Pacific Oceans, but Pelagic Sea Snakes are found from the east coast of Africa across the tropics to the west coast of the Americas. They are the only exclusively pelagic marine snake, meaning they live near the surface of the ocean but far away from land, and their distribution spans more than half of the Earth's circumference, making them the most widely distributed snake on Earth.

Artist's rendition of "float-and-wait" foraging.

I was unable to find a photograph of this behavior.

If you know of one, please let me know.

Digital painting by Stuart Jackson-Carter; www.sjcillustration.com

Although there is some debate about the amount of intent used to get there, Pelagic Sea Snakes sometimes congregate around calm areas where ocean currents converge, ("slicks"), where flotsam, debris, and pelagic organisms are often concentrated. By one 1519 explorer's account, Pelagic Sea Snakes were "innumerable" along one such slick on the west coast of Costa Rica. Pelagic Sea Snakes are "float-and-wait" predators, meaning that they passively drift in the water waiting for fishes to come near. A similar strategy is used by many terrestrial snakes, such as vipers and large pythons, except that in the open ocean, many fishes probably approach purposefully, meaning to take shelter beneath the seemingly inanimate snakes. The snakes then strike sideways or by swimming rapidly backwards. Their venom, like that of most sea snakes, is made up of only one or two exceptionally potent compounds, unlike the complex venoms of most terrestrial snakes. Partially as a result of their biodiverse habitat and immobile foraging behavior, Pelagic Sea Snakes play host to a diversity and abundance of epibionts almost twice as great as that of any other kind of sea snake.

Crustacean epibionts from Pelagic Sea Snakes

Most marine snake epibionts are invertebrates. Barnacles are ubiquitous, and familiar marine creatures such as crabs, shrimp, snails, and oysters are also found living on sea snakes, alongside more obscure marine animals such as hydrozoans (hydras) and bryozoans ("moss animals"). Polychaete worms and ticks round out the epibiont fauna, and algae, diatoms, and a type of protist called foraminiferans ("forams" for short) represent a sort of flora, although none of these organisms are true plants. Most amazing to me are two chordates, a tunicate and a clingfish, that were recently documented as epibionts of Pelagic Sea Snakes. Tunicates, also known as sea squirts, are marine filter feeders that have a sac-like body structure as adults. Tunicate larvae are free-swimming and resemble tadpoles, but at metamorphosis an adhesive disc on their "head" transforms into a stolon, or "foot", which they use to cling to a rock or, in this case, a sea snake. The pelvic fins of clingfishes are modified into a sucking disc, which they use to hold onto their snake hosts. How they avoid being eaten, I do not think anyone knows yet.

In order to keep this menagerie under control, Pelagic Sea Snakes shed frequently. On average, a Pelagic Sea Snake will shed its skin once every three weeks, whereas most other snakes go for one to two months between sheds. Additionally, while in most snakes the frequency of shedding decreases with age, it remains frequent into adulthood in Pelagic Sea Snakes. Because the open ocean is devoid of surfaces against which to rub to facilitate shedding, Pelagic Sea Snakes use a behavior known as "knotting" to initiate the process and to remove the shed skin and any associated epibionts. You can see a good example of knotting behavior in this video of a captive Pelagic Sea Snake:

Pelamis platurus never leave the water
and cannot move on land. Most that land on beaches die.

Why do so many animals live on Pelagic Sea Snakes? One explanation may be the protection associated with settling upon one of the world's most venomous serpents. Pelagic Sea Snakes are not eaten by most seabirds or fishes (although naïve Atlantic fishes will consume them, and sometimes die from it) and so neither are their epibionts. Perhaps natural selection has favored the crabs, barnacles, and tunicates that live on sea snakes over those that land on more palatable substrates. Furthermore, the complex interplay among various members of the sea snake epibiont community may allow more species to coexist there. For instance, predatory epibionts such as larval crabs may benefit the sea snakes by controlling populations of other, more detrimental epibionts, such as barnacles, which probably slow or block the update of oxygen by the snake's skin during long dives.

Sea snakes are among the most amazing of serpents, and Pelagic Sea Snakes are among the most amazing of sea snakes. From their saffron bellies to their lung, used to control buoyancy, to their roles as substrates for unique ecosystems, these snakes might just be the most incredible snakes out there.

ACKNOWLEDGMENTS

Thanks to William Flaxington, Hung-Jou Chen, Chayajit, and Stuart Jackson-Carter for their photos and digital illustrations, and to Joe Pfaller for answering my questions about sea snake epibionts.

REFERENCES

Brischoux, F. & H. B. Lillywhite (2011). Light-and flotsam-dependent ‘float-and-wait’foraging by pelagic sea snakes (Pelamis platurus). Marine Biology 158:2343-2347 <link>

Castro, J. J., J. A. Santiago & A. T. Santana-Ortega (2002). A general theory on fish aggregation to floating objects: An alternative to the meeting point hypothesis. Reviews in Fish Biology and Fisheries. 11:255-277 <link>

Graham, J. B. (1974). Aquatic respiration in the sea snake Pelamis platurus. Respiration Physiology 21, 1-7 <link>

Greene, H. W. (1997) Snakes: The Evolution of Mystery in Nature. Berkeley: University of California Press <link>

Pfaller, J. B., M. G. Frick, F. Brischoux, C. M. Sheehy, and H. B. Lillywhite. 2012. Marine snake epibiosis: a review and first report of decapods associated with Pelamis platurus. Integrative and Comparative Biology 52:296-310 <link>

Rubinoff, I. & C. Kropach (1970). Differential reactions of Atlantic and Pacific predators to sea snakes. Nature 228, 1288-1290 <link>

Zann LP, Cuffey RJ, Kropach C. 1975. Fouling organisms and parasites associated with the skin of sea snakes. In: Dunson WA, editor. The biology of sea snakes. Baltimore: University Park Press. p. 251–65

POSTSCRIPT

Cetacean photographer Eduardo Lugo captured this image of a Pelagic Sea Snake being pushed up out of the water by a dolphin, almost as if it was riding on its back:

Perhaps Pelamis is heading towards a lifestyle as a dolphin epibiont? Lugo says they were swimming with the dolphins from a Wildlife Connection ecotour boat when the dolphins decided to play with the snake.

Life is Short, but Snakes are Long by Andrew M. Durso is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.

What the State Snakes Should Be: Part II

Click here to read this post in Spanish!

Haga clic aquí para leer este blog en español!

Several weeks ago, I debuted Part I of 'What the State Snakes Should Be', inspired by 'The State Birds: What They SHOULD Be' from thebirdist.com. With apologies for the late follow-up (I've been on vacation), I now present...

Part II

26. Montana. Bullsnake (Pituophis catenifer)

Pituophis catenifer

These large, harmless, common snakes are known for their loud hiss, which they augment using a flap of skin on the end of their windpipe. They also rattle their tail against dry leaves in order to intimidate their would-be predators. Also known as gophersnakes or blowsnakes, they are commonly mistaken for rattlesnakes, which they superficially resemble. Bullsnakes are found throughout the plains of central and eastern Montana, as well as in the Bitterroot Valley of western Montana. Appropriate to Big Sky Country, bullsnakes are among the longest of North American snakes, reaching incredible lengths of 9 feet as adults! Radiotelemetry studies have found that individuals spend up to 90% of their time in underground burrows, so these snakes must be quite abundant in areas where they are frequently encountered.

27. Nebraska. Western Hog-nosed Snake (Heterodon nasicus)

Heterodon nasicus

I studied these snakes in Illinois for my Master's degree, but nowhere have I seen them so abundant as in the Nebraska sandhills. Western Hognoses love sand, in which they burrow and lay their eggs. They also frequently unearth the buried eggs of other species, including those of lizards and turtles. Like their eastern cousins, they also eat amphibians and possess elaborate anti-predator displays. These snakes are easily observed in open areas during the day by anyone willing to hike around the beautiful sandhills region of the Cornhusker State.

28. Nevada. Desert Nightsnake (Hypsiglena chlorophaea)

Hypsiglena chlorophaea

Known for its nightlife, the Silver State is well-represented by Nightsnakes, which are secretive residents of deserts throughout the west. Nightsnakes are nocturnal, as evidenced by their vertical pupils, and eat lizards and amphibians, as well as lizard and snake eggs on occasion. They are most active on moonless nights after rain. Few people will have seen a Nightsnake, but they occur throughout Nevada. I also heard that the Nevada Nightsnakes might be a competitive team against the Mississippi Mudsnakes this year.

29. New Hampshire. Eastern Hog-nosed Snake (Heterodon platirhinos)

Heterodon platirhinos (dark phase)

Eastern Hognoses are well known for their elaborate anti-predator behavior, which involves vomiting, defecating, and flipping over onto their backs. Research in the southern part of the Granite State has shown that prey likely limits their distribution in the northeast, as they are found on barrier islands with small amphibians but not those without. A recent radio-telemetry study at the New Boston Air Force Station revealed much about the habitat preferences of these snakes. Overall optimal habitat was identified as hemlock forests having continuous canopy and understory architecture interspersed with fine-scale openings, in close proximity to wetlands and with a high density of leaf litter, debris, and rocks as well as homogeneous surface temperatures within critical thermal limits. Eastern Hognoses mostly eat amphibians and occur in two color phases, dark and patterned.

30. New Jersey. Northern Pine Snake (Pituophis melanoleucus)

Pituophis melanoleucus

Much of the pioneering research on pinesnake biology has taken place in the New Jersey Pine Barrens. We know a lot about the surprisingly social lives of these large snakes - for instance, they communally bury their eggs in habitual spots used year after year by the same females. Pinesnakes prefer sandy, well-drained soils such as those in the the New Jersey Pinelands, which may provide residence for some of the largest populations of pinesnakes in the Northeast. Their reputation as ornery is mostly undeserved, much like that of their fellow Garden State residents (something I can admit despite having been born in neighboring New York).

31. New Mexico. New Mexico Blindsnake (Rena dissectus)

Rena dissectus

Having just been to New Mexico, I know first-hand that there are a lot of snakes there to choose from. In the interest of representing the widest range of phylogenetic diversity, I decided that the New Mexico Blindsnake should represent the state, in part because I was fortunate enough to find one while I was there (my first wild scolecophidian!) and in part because they can be found in only a few states in the US. These diminutive serpents eat ants and termites and burrow in loose soil. This species was discovered by E. D. Cope in 1896 along a road to a silver mine at Lake Valley, New Mexico. Runners up: Narrow-headed Gartersnake (Thamnophis rufipunctatus), Mexican Gartersnake (Thamnophis eques), Chihuahuan Nightsnake (Hypsiglena jani), New Mexico Ridge-nosed Rattlesnake (Crotalus willardi obscurus).

32. New York. Brownsnake (Storeria dekayi)

Storeria dekayi

You might think the Empire State would be better typified by a grander snake, but there are several good reasons that Brownsnakes are special to New Yorkers (or should be). The first specimen of a Brownsnake was collected in New York by Dr. James DeKay, a zoologist and author of the 1842-1844 book Zoology of New York. He found the snake while it was ""swimming across a large bay on the Northern coast of Long Island." John Holbrook, the father of North American herpetology, named the snake for DeKay, making it the only North American snake whose name is a double patronym (the genus Storeria being in honor of David Storer, a Massachusetts herpetologist; see Massachusetts).

33. North Carolina. Southern Hog-nosed Snake (Heterodon simus)

Heterodon simus

Southern Hog-nosed Snakes aren't doing too well throughout most of their range. Habitat destruction and degradation, fire ants, and mortality on roads are among their major threats. The Sandhills of North Carolina are their stronghold, and we'd like to keep it that way. The North Carolina Herp Society supports Project Simus, a non-profit research program with the goal of monitoring Southern Hognoses in NC and learning more about their biology through radio telemetry and other techniques. North Carolina recently named a State Frog, a State Salamander, and a State Marsupial, so a State Snake could be next! Runners up: Carolina Pygmy Rattlesnake (the beautiful red phase) or Outer Banks Kingsnake or Carolina Watersnake (both endemic subspecies found in the barrier islands).

34. North Dakota. Racer (Coluber constrictor)

Coluber constrictor

Racers are one of North America's most widespread snakes, found in every state except Alaska and Hawaii. They are highly variable in color, ranging from brown to black to green to blue. In North Dakota, they are greenish-blue to gray with a bright yellow belly and a white chin patch. They aren't called Racers for nothing: their speed is astounding and it is common to see these snakes for just a second or two as you walk through a grassland. Racers inhabit the sagebrush prairies of western North Dakota and are commonly found near sources of water. They have large eyes which aid them in their pursuit of their prey during the day. Young racers have a distinctive speckled pattern that slowly fades as they mature. Due to their widespread nature, this species might be a good candidate for a national snake as well.

35. Ohio: Kirtland's Snake (Clonophis kirtlandii)

Clonophis kirtlandii

These small and interesting snakes were originally slated for Indiana, until I learned that not only were many of the seminal studies of them carried out in the Buckeye State and that they are named for an Ohio politician, malacologist, and co-founder of the Cleveland Museum of Natural History, Jared Potter Kirtland. Kirtland's Snakes are found only in the midwest, where they inhabit crayfish burrows. Because of the intensive agriculture that dominates rural areas of Indiana and other midwestern states, some of the best known Kirtland's Snake populations are found in urban areas. Runners up: Lake Erie Watersnake (an endemic subspecies), Black Racer (actual State Reptile).

36. Oklahoma. Western Diamond-backed Rattlesnake (Crotalus atrox)

Crotalus atrox

Much maligned symbol of the west, Western Diamondbacks are in much better shape than their slightly larger eastern cousins, in spite of heavy collection in some areas for use in rattlesnake roundups (festivals with the express purpose of executing as many rattlesnakes as possible in the misguided belief that this somehow makes people in the surrounding area safer). Corporate sponsorship and economic contributions to local economies have helped these festivals persist in the Sooner State and others, much to the detriment of wild rattlesnake populations. In fact, Western Diamondbacks and other rattlesnakes are not nearly as dangerous as cars, cigarettes, dogs, or many other things that people willingly accept as part of their lives. Granted, if one bites you you'd best get to the emergency room sooner than later, but they hardly deserve their vicious reputation, and confer many benefits to those with whom they share the landscape, including pest control.

37. Oregon. Common Gartersnake (Thamnophis sirtalis)

Thamnophis sirtalis

Although these snakes can be found in every state except Arizona, Hawaii, and Alaska, I have never seen more beautiful Common Gartersnakes than those in Oregon. Add that to the incredible coevolutionary relationship between these snakes and their toxic newt prey discovered in Oregon, and you have a good recipe for a state snake. Common Gartersnakes are capable of resisting the neurotoxic effects of tetrodotoxin, which paralyzes the muscles and nerves of most other predators. More resistant gartersnakes live in areas where newts are more toxic, are more brightly colored, and crawl more slowly.

38. Pennsylvania. Eastern Wormsnake (Carphophis amoenus)

Carphophis amoenus

It's tempting to put this smallest eastern snake for Rhode Island, but because it was discovered in the Keystone State by the famous Philadelphian and entomologist Thomas Say in 1824, I think it's more apt for Pennsylvania. Say described its opalescent scales and called it "a very pretty and perfectly harmless serpent," noting that "it is found beneath stones and prostrate logs, but not very frequently." Wormsnakes eat invertebrates and so are beneficial to have in and around your garden. Runner-up: Narrow-headed Gartersnake (Thamnophis brachystoma), found almost exclusively in Pennsylvania.

39. Rhode Island. Ring-necked Snake (Diadophis punctatus)

Diadophis punctatus

At least in the east, these snakes are small, with gorgeous yellow color beneath marked with black spots. Farther west, they are orange or red instead. The yellow ring around the neck gives the species its name. Described by Linnaeus in the 11th edition of his Systema Naturae, it was one of the first species of North American snakes known to European biologists. Ringnecks are usually found close to water underneath rocks and logs, although they rarely swim. Rhode Islands's many historic stone walls are ideal habitat for this species. Eating salamanders and invertebrates, these snakes are harmless and beneficial. Don't miss the playoff game between the Rhode Island Ringnecks and the Nevada Nightsnakes!

40. South Carolina. Cornsnake (Pantherophis guttatus)

Pantherophis guttatus

The Cornsnakes of the famous Okeetee Club of southern SC are famed for their bright colors. Popular pets, these snakes have been bred in captivity to produce a variety of color morphs not found in the wild. Cornsnakes eat lizards and small mammals and are named for their highly contrasting ventral pattern, which resembles an ear of Indian corn. Carl Kauffeld first wrote of the Okeetee Club in his book Snakes and Snake Hunting, wherein he recounts several of his experiences trying to find cornsnakes in their natural habitats.

41. South Dakota. Prairie Rattlesnake (Crotalus viridis)

Crotalus viridis

These rattlesnakes are fairly common in the Great Plains of the central USA wherever rocky outcrops (including man-made ones such as railroad track beds) provide suitable hibernation sites. They are closely related to Western Rattlesnakes (see Wyoming), with which they shared a common ancestor about 9 million years ago. Following their rise, the rain shadow of the Rocky Mountains fell over central North America, causing a drying of the climate that led to the gradual replacement of open woodlands by prairie. Differentiation of the eastern form involved isolation plus adaptation to the expanding grasslands east of the Rocky Mountains. Today Prairie Rattlesnakes are common across the western two-thirds of South Dakota, where they prey heavily on rodents.

42. Tennessee. Rough Greensnake (Opheodrys aestivus)

Opheodrys aestivus

Rough Greensnakes are beautiful denizens of riparian woods throughout the Volunteer State. They were first recorded from "Carolina", which included Tennessee at the time. Also known as vine snakes, these arboreal, camouflaged snakes eat insects and spiders. Because they are so well-camouflaged, the best way to spot them is often at night using a flashlight. Difficult to keep in captivity, I would volunteer to study these any time, as they are among the most graceful and popular of snakes.

43. Texas. Gray-banded Kingsnake (Lampropeltis alterna)

Lampeopeltis alterna

Texas has 85 species of snakes, more than any other state. I thought that Texans would like to have the longest or largest snake for their state snake (they'd probably call it their national snake), but both, as well as the largest rattlesnake, are more iconic of other places. As such, they will have to do with one of the most beautiful and coveted, the Gray-banded Kingsnake. These secretive snakes are found only in dry, rocky areas of the Trans-Pecos and Chihuahuan regions of the state, where they are active at night. Although popular in the pet trade, very little is known about the ecology of these snakes in the wild. Much of their habitat is inaccessible, made more so by strict laws regulating the recreational pursuit of snakes (herping or snake-hunting) in the state of Texas. Runners-up: Speckled Racer (Drymobius margaritiferus), Concho Watersnake (Nerodia paucimaculata), Brazos Watersnake (Nerodia harteri), Texas Indigo Snake (Drymarchon corais).

44. Utah. Wandering Gartersnake (Thamnophis elegans)

Thamnophis elegans

Because I currently live in Utah, I can attest to the ubiquity of these snakes almost throughout the state. So named because of their propensity to stray far from water, Wandering Gartersnakes have something in common with the early Mormon settlers of the Beehive State, who emigrated from their original homeland in New York through the Midwest to eventually end up in what is today Utah. Wandering Gartersnakes eat fish, frogs, and small mammals, and lack the resistance of some of their congeners to newt toxin because they do not co-occur with newts over much of their range.

45. Vermont. Black Ratsnake (Pantherophis obsoletus)

Pantherophis obsoletus

Familiar to many in the eastern US, ratsnakes are on the ropes in Vermont. Records from the west-central part of the state date from recent decades, with possible isolated populations in other areas of the Green Mountain State (though these records could represent releases of captive animals). Ratsnakes have been designated a Species of Greatest Conservation Need in Vermont’s Wildlife Action Plan. Popular in captivity, we are just beginning to learn about the ecology of wild ratsnakes, which are highly accomplished climbers and important nest predators. Their communal nesting ecology at high latitudes and their intriguing foraging and social behaviors are likely just the tip of the iceberg.

46. Virginia. Smooth Earthsnake (Virginia valeriae)

Virginia valeriae

These small brown snakes come in two types, rough and smooth. The Rough Earthsnake (Virginia striatula) is found in the southeastern part of the state, whereas the more widespread Smooth Earthsnake (Virginia valeriae) is found across the eastern two-thirds, and also in isolated populations in the western tip. Virginia also shares with adjacent states an unusual population of Smooth Earthsnakes, called Mountain Earthsnakes (V. v. pulchra or, sometimes, simply V. pulchra), found in high-altitude glades in Highland County, Virginia, and adjacent WV, MD, and PA. Mountain Earthsnakes have scale characteristics intermediate between the other two, although they are more closely related to Smooth Earthsnakes.

47. Washington. Sharp-tailed Snake (Contia tenuis)

Contia tenuis

Sharp-tailed Snakes are small and locally common. They are named for the needle-like spine on the end of their tail, which nevertheless is not actually very sharp and with which they certainly cannot harm a human. This is a good snake to have around your garden, as they eat slugs and other invertebrates harmful to plants. Sharp-tails are mostly found in Oregon and California, but an isolated population occurs in central Washington, where dozens of individuals can sometimes be found together underneath cover objects. Sharp-tailed Snakes may turn out to be more widespread in Washington, especially since they were first discovered in 1852 by members of the U.S. Exploring Expedition near Puget Sound, a region from which no further specimens have been found. Perhaps state snakehood would promote further exploration.

48. West Virginia: Timber Rattlesnake (Crotalus horridus)

Crotalus horridus

Kudos to West Virginia for choosing a snake for their state reptile in real life! As a reward, they get to keep it. The Timber Rattlesnake isn't an inapt choice, as they are found in mountainous forests almost throughout the state, wherever suitable overwintering habitat exists. A recent analysis of the diet of Timber Rattlesnakes in the northeastern US suggested that they may help regulate tick populations through consumption of their mouse hosts, thereby probably reducing the risk of human exposure to Lyme disease and other tick-borne pathogens. Runner up: the other (Rough) Earthsnake (Virginia striatula).

49. Wisconsin. Butler's Gartersnake (Thamnophis butleri)

Thamnophis butleri

Butler's Gartersnakes are found in open-canopy wetlands in the southern Great Lakes region. In reality, enough Wisconsinites dislike Butler's Gartersnakes for getting in the way of development in the Milwaukee area that it's got about as much of a chance of getting chosen as the state snake as the Spotted Owl has of becoming the state bird of Oregon. However, efforts to manage and preserve the remaining habitat might just succeed, and could be significantly helped along by placing a little more value on these little snakes. In the land of visionary land manager Aldo Leopold, I agree with this One Wisconsin Now blogger that good stewardship should trump special interests when it comes to Butler's Gartersnakes.

50. Wyoming. Western Rattlesnake (Crotalus oreganus)

Crotalus oreganus

These relatively small rattlesnakes are fairly common in the arid west anywhere that rocky outcrops provide suitable hibernation sites. They are closely related to Prairie Rattlesnakes (see South Dakota). These two species shared a common ancestor about 9 million years ago, populations of which were separated by the rise of the Colorado Plateau during the Miocene epoch. Volcanic activity in the southern area of the plateau prevented contact between the two populations. Further differentiation of the western form into six subspecies involved adaptation to various cooler climates west of the Rocky Mountains. The subspecies that occurs in the Cowboy State today is the Faded Midget Rattlesnake, a diminutive snake with a somewhat subdued pattern.

Feel free to chime in with your opinion about what your state's snake should be, if it differs from mine. What do you think the National Snake would be, if the USA had one? Vote in the poll at the right, or share your opinion in the comments below. If you missed Part I, check it out!

ACKNOWLEDGMENTS

Thanks to Pierson Hill, Todd Pierson, JD Willson, Taylor Henry, Dan Johnson, James Turek, and Gary Nafis for use of their photographs.

Life is Short, but Snakes are Long by Andrew M. Durso is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.