How many snakes are venomous and how many are constrictors?

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Data from all 3,631 living species of snakes in The Reptile Database

as of April 2017. I made the assumption that prey-killing behavior

didn't vary within genera, so if I found data for one species in a genus

I applied it to all others in the absence of specific data for those species.

Many people are aware that some snakes constrict their prey, and others use venom to kill their prey. Recently, somebody asked me what the breakdown was, and I had to admit that I didn't know exactly. My initial estimate was that 20% were venomous in a way that is medically-significant to humans, and that probably a similar number of species are opisthoglyphs that use venom that is not life-threatening to humans to subdue their prey (with a decent number of these pending discovery, confirmation, or further investigation). Estimating the percentage of constrictors was more difficult, but I suspected that it was no more than the percentage of snake species that use venom, and probably somewhat less. A lot of people don't realize that there is a huge third category of snakes that just seize their prey and swallow it alive, sometimes subduing it first by crushing it with strong jaws or pinning it to the ground with a coil (which hardly counts as constriction but could be an evolutionary precursor).

This inspired me to do some literature searching, and as I suspected nobody has ever attempted to estimate the exact percentages of snake species that use each kind of prey-killing behavior. As such, I have prepared a preliminary analysis, the full contents of which I intend to make publicly available after peer review. I hope that doing so will stimulate others to publish their observations of feeding behavior in poorly-known snakes (of which there are many), and add to the long history of discussion about the evolution of snake feeding modes, most of which took place before we had a solid grasp on the evolutionary relationships of extant snake families.

I found that the answer to this question is not as simple as it may seem. Many snakes unambiguously use venom or constriction, but many use neither, and some use both! Of course the data are not as detailed or abundant as we would like. What follows is a break-down of the categories I used, and some interesting exceptions that I uncovered.

Constrictors

Unambiguous constrictors make up just 11% of snake species, but include several well-known groups that are common in the popular consciousness, in zoos, and in the pet trade, including:

• Boas: 61 species, including the eponymous Neotropical Boa constrictor, anacondas (Eunectes), and smaller tree and rainbow boas (Corallus, Epicrates, Chilabothrus) as well as several (sub)families of booid snakes from various and sundry locations around the world—Candoia from New Guinea and Melanesia, sand boas (Eryx) from northeast Africa, the Middle East, and southwestern Asia, Charina and Lichanura from North America, Ungaliophis and Exiliboa from Central America, Acrantophis and Sanzinia from Madagascar, and Calabaria from tropical west-central Africa.
• Pythons: 40 species from Africa, Asia, and Australia
• Ratsnakes, kingsnakes, and close relatives: 43 species of New World colubrine colubrids in the clade Lampropeltini and their Old World counterparts, including:
• Lampropeltis kingsnakes, the consummate constrictors, which prey on other constricting snakes and are rarely, if ever, out-constricted because they are capable of exerting 20 kilopascals of pressure, twice as much as a ratsnake (average 10 kPa)
• southwestern North American species in the genera Pseudelaphe, Arizona, Rhinocheilus, Bogertophis, and Senticolis
• Pantherophis ratsnakes, as well as their sister taxon Pituophis (pine, bull, and gophersnakes), which often press their prey against rocks or other solid objects
• 2 species of live-bearing Eurasian Coronella and their close relative, the Frog-eating Rat Snake Oocatochus rufodorsatus from eastern Russia, Korea, Taiwan, and northeastern China
• 26 species of Old World Elaphe and their relatives in the genera Zamenis, Orthriophis, Oreocryptophis, Euprepiophis, and Archelaphe.

as well as some more obscure groups:

Anilius scytale constricting an amphisbaenian
From Marques & Sazima 1998

• Tropidophiids or "dwarf boas", which are not closely related to boids and certainly evolved constriction independently (34 species)
• Their close relative Anilius scytale (sort of; this snake has been observed to constrict large prey such as amphisbaenians)
• Loxocemus bicolor, the Mexican burrowing snake, a close relative of pythons
• Two speceis of Asian sunbeam snakes (genus Xenopeltis), which are also closely related to pythons
• At least some (maybe all) Asian pipesnakes (family Cylindrophiidae)
• Filesnakes (genus Acrochordus), which don't necessarily kill fish by constricting them but use their coils to hold them while they swallow
• some lamprophiine colubrids (especially the well-known African house snakes Lamprophis and Boaedon)
• the colubrine colubrid tribe Lycodontini (mostly wolf snakes, genus Lycodon)
• some snail-eating snakes (Dipsas) coil around snails as they pry them out of their shells
• even Wandering Gartersnakes (Thamnophis elegans)—sometimes! (more below)

These groups of snakes vary considerably in how often they employ constriction to kill their prey. Some probably use it almost all the time (although even ratsnakes eat prey that they don't constrict, such as bird eggs), whereas others use constriction only rarely, when encountering an unusually large or dangerous prey item relative to their size and strength (for example, one study showed that species of Python, Boa, Pantherophis, and Lampropeltis always constricted mice if they were at least 90% the diameter of the snake's head). Some, such as Regina alleni and Acrochordus filesnakes, may use constriction more so to immobilize the prey than to kill it/it probably doesn’t work that well under water (although Wandering Gartersnakes usually killed mice before eating them).

It seems that mammal-eating is a driver of the evolution of constriction in many cases: species that eat mammals are the only members of their genera/families that use constriction (Thamnophis elegans, Boiga irregularis, Lamprophis/Boaedon, some members of the Oxyrhopus/Clelia/Pseudoboa clade) and both these and species that are nested within mammal-eating clades but have shifted to other prey (Lampropeltis extenuatum, Elaphe quadrivirgata, Cemophora coccinea¹) tend to have more variable, less efficient constricting behavior that is generally only used to immobilize rather than to kill prey, if it is used at all. As Alan de Queiroz and Rebecca Groen put it: “Thamnophis elegans are not finely tuned constricting machines” and “Numerous trials in which a garter snake, holding a mouse in its jaws, was chaotically thrown about by the prey's movements support our interpretation that long constriction latencies do not reflect adaptive plasticity in T. elegans.”. Constriction probably functions to reduce the cost of feeding in terms of time, energy, and/or the probability that the prey will harm the snake.

Conspicuously not in this category, we have the poorly-named and misleading North American Racer, Coluber constrictor, which is not a constrictor (thanks for nothing, Linnaeus).

Venom

Black Mamba (Dendroaspis polylepis) eating a bird

It's pretty clear which snakes use strong venom to subdue their prey; most of these are dangerously venomous to humans and so we're well aware of them. There are five major groups:

• Viperids (341 species), including well-known pit vipers such as rattlesnakes, copperheads, and cottonmouths
• Elapids (359 species), including coralsnakes, cobras, mambas, kraits, sea snakes, and diverse terrestrial Australian snakes ranging from death adders (genus Acanthophis) to bandy-bandys (genus Vermicella)
• Genus Atractaspis (21 species), the stiletto snakes now known to be lamprophiids, which stab backwards with their fangs, mouth closed, to envenomate prey in subterranean burrows
• Non-front-fanged colubrine colubrids, most notably boomslangs (Dispholidus typus), twigsnakes (genus Thelotornis), and probably their close relatives in the genus Thrasops, all of which have many functional characteristics of front-fanged snakes while their elongated teeth remain at the rear of the (albeit rather short) maxilla
• some Asian natricine colubrids in the genera Rhabdophis, Macropisthodon, and Balanophis, which in addition to being (in a few cases lethally) venomous, also have the distinction of being among the only known poisonous snakes

Also, many snakes use venom to subdue their prey but are not dangerous to humans, either because they have fangs in the back of their mouth, have venom that is not adapted for causing physiological damage to mammals, or both. These include:

• numerous dipsadine colubrids from the Caribbean and Central and South America, such as Xenodon, Thamnodynastes, Hydrodynastes, Coniophanes, Erythrolamprus, Rhadinaea, Leptoderia, and Apostolepis (and a few from North America, such as Heterodon and Hypsiglena)
• some colubrine colubrids (genera such as Boiga, Leptophis, Tantilla, Toxicodryas, Platyceps, Oxybelis, Hierophis, Crotaphopeltis, Drymobius, Chilomeniscus, Ficimia, and Gyalopion) as well as the Asian genera Ahaetulla and Chrysopelea, sometimes split into a different subfamily (Ahaetullinae)
• at least some natricine colubrids, such as Paratapinophis praemaxillaris and some North American gartersnakes (Thamnophis)
• many species in the family Homalopsidae, 53 species of southeast Asian semi-aquatic snakes, some of which are also well-known for pulling apart large crabs and eating pieces of them
• some (maybe most) lamprophiids, including aparallactines (Amblyodipsas, Aparallactus, Micrelaps, Polemon, Xenocalamus), lamprophiines (Gonionotophis), psamophiines (Mimophis, Psammophis), and the weird genus Psammodynastes ("mock viper")

and probably many more. It's actually possible that this is the largest group, because some of the "unknown" and "neither" species probably actually belong here. An interesting exception are Turtle-headed Seasnakes (Emydocephalus annulatus) and Beaded Seasnakes (Aipysurus eydouxii), which eat fish eggs and have mostly lost their venom, fangs, and venom glands. Another example of a reduction in fangs are some fossorial species of Tantilla, which have only slightly enlarged and faintly grooved rear maxillary teeth, in contrast to the more well-developed rear fangs of most other members of this large genus. These snakes appear to specialize on beetle larvae rather than on centipedes, although no one has looked to see if their venom is any different as a result.

Neither

Dipsas indica coiling around a snail, from Sazima 1989

Most snakes (38% of species) seize their prey and swallow them alive. Generally these snakes are eating prey that are much smaller than they are, which lack serious physical defenses (although many of them may have chemical defenses that the snakes circumvent in other ways, such as through toxin resistance). These include:

• Scolecophidians: Almost 450 species of blindsnakes that eat ant and termite larvae and pupae
• Uropeltids or Shield-tailed Snakes: 55 species that eat almost exclusively earthworms
• Snail-eating snakes in the family Pareidae: 20 southeast Asian species with asymmetrical jaws
• About 300 species of mostly South American dipsadine colubrids that eat soft, gooey things like slugs, snails, earthworms, or frog eggs, including:
• the most speciose genus of snakes, Atractus (currently with 140 species)
• the genus Geophis, currently in a four-way tie for the 5th-most speciose snake genus with 50 species
• some slender arboreal snakes in the genus Sibon, which crawl backward through crevices to wedge snails into them, providing an anchor against which they use their body muscles to pull out the soft parts
• Asian Thermophis
• North American Carphophis and Contia
• Most Old and New World natricine colubrids
• most gartersnakes (Thamnophis)
• watersnakes (Nerodia) and their relatives (Regina, Seminatrix, Clonophis, Tropidoclonion)
• slug-eating Storeria
• Asian ecological analogues (e.g., Amphiesma, Hebius, Opisthotropis, Xenochrophis)
• Numerous colubrine colubrids, such as:
• New World racers and coachwhips (Coluber)
• Indigo snakes (Drymarchon), which are well-known for crushing their prey in their strong jaws
• Indian ratsnakes (Ptyas)
• the Mole Snake (Pseudaspis cana)
• Egg-eating snakes (Dasypeltis), which have no need to kill the bird eggs that they eat or prevent them from escaping
• Calamariinae, an obscure subfamily of 89 species of colubrids from Asia that are thought to eat mostly earthworms

Some of the aforementioned goo-eaters do use their coils to support the shells of snails while they pry out the soft innards. Dipsas coils around the snail’s shell and Sibynomorphus use as s-shaped loop of their body to support the shell, whereas some Sibon crawl backward through crevices to wedge snails into them, providing an anchor against which they use their body muscles to pull out the soft parts.

Both

Finally, there are some really interesting examples of snakes that use both venom and constriction to subdue their prey, although not always at the same time. Perhaps most impressive but least well-documented in the scientific literature are two viper species that sometimes use constriction in conjunction with venom: Ovophis monticola and O. okinavensis².

Pseudonaja textilis constricting a mouse
From Mirtschin et al. 2006

A review by Rick Shine & Terry Schwaner brought together data on numerous Australian elapids that, although they clearly have and use venom, also use their coils to subdue and hold prey while envenoming it. In many of these species, including tiger snakes (Notechis), brown snakes (Pseudonaja), curl/myall snakes (Suta), whip snakes (Demansia), Australian coral snakes (Simoselaps), crowned snakes (Cacophis), and olive seasnakes (Aipysurus laevis), the coils are not used alone as the primary method of prey subjugation, and one recent paper suggested that we think of them as "part of a 'combined arsenal' of prey subjugation strategies".

To explain the "apparent paradox of why a species should use both venom and constriction to subdue its prey", Shine & Schwaner offered three possible non-mutually-exclusive explanations:

1. The venom may be of low toxicity and thus slow to act, so holding onto the prey with either jaws or coils might allow more venom to be injected
2. Species with short fangs, such as Pseudonaja, and/or that feed on on heavily armored prey , such as skinks, may use constriction to give themselves additional time to find a "chink in the armor" and envenomate their prey
3. Using constriction in addition to venom may prevent snakes from losing track of bitten and envenomated prey that escape, or from being harmed by retaliating prey that are held onto

The Australian elapids recorded to use constriction feed mainly on lizards and frogs, although mammals are common prey items of Pseudonaja and Notechis. Puff Adders (Bitis arietans) choose to release large rodents and rabbits, but hold onto smaller prey, although they have not been reported to use constriction (and given their specialized body shape, they probably do not, nor do they need to since they are equipped with long fangs, strong venom, and strike-induced chemosensory searching). However, immobilizing prey with coils probably plays a larger role in prey subjugation for many rear-fanged species with slower-acting venom, such as:

• colubrine colubrids Boiga irregularis, Macroprotodon, Platyceps gracilis, Stegonotus, Telescopus, Trimorphodon
• dipsadine colubrids from the Caribbean (Alsophis, Cubophis), Central & South America (Clelia, Helicops, Imantodes, Oxyrhopus, Philodryas, Tropidodryas, Siphlophis, Phimophis, and Pseudoboa), and North America (Diadophis, Farancia)
• the sibynophiine colubrid Sibynophis collaris
• some homalopsids, like Fordonia, Hypsiscopus, and Myron
• a few lamprophiine lamprophiids, such as Lycophidion
• pseudaspine lamprophiids Pseudaspis and Pythonodipsas
• some pseudoxyrhophiine lamprophiids Leioheterodon and Madagascarophis
• some psammophiine lamprophiids (e.g., the Montpellier Snake and its relatives in the genus Malpolon, Hemirhagerrhis, Psammophis, and Rhamphiophis)
• even Wandering Gartersnakes (Thamnophis elegans)—sometimes!

Elaphe quadrivirgata not constricting a frog (Rana ornativentris)
Mori (1991) showed that these snakes constrict large mice,
pin small mice with a single coil, and swallow frogs alive

In many cases, only large endothermic prey (usually mammals) are constricted, whereas snakes will swallow small, easily subdued prey alive. Even some specialized constrictors will consume small prey whole, suggesting that almost all snakes can change strategies depending on what type of prey they are subduing. The bottom line is that, if you're a snake that's eating mammals, you need to have either constriction or venom, and maybe both, because:

1. Mammals are big, or at least a lot of snakes like to eat mammals that are relatively large compared to their body size
2. They are endotherms with the metabolic capacity for sustained struggling
3. They can fight back with sharp teeth and strong jaws capable of seriously injuring or killing a snake, in a way that a frog or a lizard cannot

This generalization is supported by observations showing that mammals tend to be killed by constriction prior to being swallowed more often than prey such as frogs, and that larger prey tend to be killed by constriction first, then swallowed. Evidently the amount of struggling is one cue used by Thamnophis elegans to decide whether or not to constrict prey. Experiments carried out by Akira Mori and others have shown that "the degree of such behavioral flexibility is, to some extent, species-specific, and it has been suggested that dietary specialists change their behavior more efficiently than dietary generalists, especially when they are young".

Unknown

After my initial pass at collecting these data (during which I made several sweeping assumptions, some of which later turned out to be oversimplifications), I was left with 36% of species unknown. Following a more thorough literature search, I managed to get this down to 10%, which is still 363 species of snakes. In many cases I made assumptions based on generalizations about the biology of groups of snakes—for instance, I assumed that all scolecophidians use neither constriction nor venom, that all vipers use venom, and so forth. But many dipsadine and colubrine colubrids, and many lamprophiids have not been directly studied, and I could find no reports in the literature about their feeding habits. In some cases we don't even know what they eat, and ecological diversity in these groups is very high, such that there are few consistent patterns that I could use to infer prey subjugation mode for these 370 species. Teach yourself about obscure snakes and help fill in the blanks!

A few examples:

• anomochilids (dwarf pipesnakes)—we don't even know what they eat
• many Malagasy pseudoyrhophiine lamprophiids (e.g., Ithycyphus, Alluaudina)
• lamprophiids from mainland Africa, such as Bothrolycus, Chamaelycus, and Dendrolycus
• obscure dipsadines—e.g., Cryophis, Tantalophis
• obscure colubrines—e.g., Bamanophis, Hemerophis
• most of the xenodermids (Fimbrios, Parafimbrios, Stoliczkia, Xylophis)
• species known only from a few specimens, like Xenophidion

Evolution of prey subjugation strategies in snakes

Phylogenetic tree from Greene 1994
For an overview of some of the updates, click here

The most recent similar review was done by Harry Greene in 1994, in which he revised earlier hypotheses he put forth with Gordon Burghardt in the journal Science 16 years before. We now know a lot more about the snake family tree than we did in 1994, particularly the fine details of relationships within the Caenophidia. Overall, the basic pattern has held up rather well—constriction evolved first in basal alethinophidians during the late Cretaceous, accompanying or preceding most other evolutionary innovations that permit snakes to consume large prey, such as kinetic skulls. Greene pointed out that this was before the origin of rodents, often mentioned as potentially relevant to the evolution of snake prey-killing behaviors. Constriction was then lost at least twice—once in uropeltids (which feed underground on earthworms, although I'm not actually aware of any detailed observations of uropeltid feeding behavior) and at least once in basal colubroids, where it might have been  at first replaced by venom. Venom was then subsequently lost in numerous caenophidian lineages, replaced by re-evolution of constriction in some or by other specializations (tooth diastemata for holding skinks, egg-eating) in others, and in some caenophidian lineages snakes use both as appropriate, sometimes together (or they may elect to use neither even if both are available).

Both constriction and venom reduce the cost of feeding in terms of time, energy, and/or the probability of the prey harming the snake, but in constricting snakes, everyday locomotion and large prey neutralization are coupled, whereas in venomous snakes they are independent (snakes don't use their fangs to get around). This could be one reason why venom as an evolutionary innovation led to a more speciose radiation of snakes; it's also more susceptible to evolutionary arms races, because prey can evolve resistance to certain venom compounds, but not to constriction. Specialization for constriction is more than just behavior—constricting species also have more vertebrae per unit length than non-constricting species. And there are costs to both, which must be outweighed by the benefits of that defining snake trait: being able to consume prey almost as large, and sometimes much larger, than yourself!

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1 An interesting exception are Scarletsnakes, Cemophora coccinea, the closest relatives of kingsnakes, which feed mostly on reptile eggs but also use their coils to hold lizard prey in the rare instances when they eat them. It is certain that Scarletsnakes evolved from constricting ancestors but because they almost never eat prey that need to be killed beforehand, evidently they rarely constrict.^↩

---

2 okinavensis has been shown not to be closely related to other Ovophis, but no new genus has yet been created for it because more data are needed.^↩

ACKNOWLEDGMENTS

Thanks to Karen Morris for asking me this question, and to Alpsdake and Danny Davies for the use of their photos.

SELECTED REFERENCES

For a full list of all the references I consulted in preparing this post, click here

Andrade, R. d. O. and R. A. M. Silvano. 1996. Comportamento alimentar e dieta da "Falsa-coral" Oxyrhopus guibei Hoge & Romano (Serpentes, Colubridae). Revista Brasileira de Zoologia 13:143-150 <full-text>

Auffenberg, W. 1961. Additional remarks on the evolution of trunk musculature in snakes. The American Midland Naturalist 65:1-16 <full-text>

Bealor, M. T. and A. J. Saviola. 2007. Behavioural complexity and prey-handling ability in snakes: gauging the benefits of constriction. Behaviour 144:907-929 <ResearchGate>

Bealor, M. T., J. L. Miller, A. de Queiroz, and David A. Chiszar. 2013. The evolution of the stimulus control of constricting behaviour: inferences from North American gartersnakes (Thamnophis). Behaviour 150:225-253 <full-text>

de Queiroz, A. and R. R. Groen. 2001. The inconsistent and inefficient constricting behavior of Colorado western terrestrial garter snakes, Thamnophis elegans. Journal of Herpetology 35:450-460 <full-text>

Franz, R. 1977. Observations on the food, feeding behavior, and parasites of the striped swamp snake, Regina alleni. Herpetologica 33:91-94 <full-text>

Gans, C. 1976. Aspects of the biology of uropeltid snakes. Pages 191-204 in A. d. A. Bellairs and C. B. Cox, editors. Morphology and Biology of Reptiles. Linnean Society Symposium Series No.3. Academic Press, London.

Götz, M. 2002. The feeding behavior of the snail-eating snake Pareas carinatus Wagler 1830 (Squamata: Colubridae). Amphibia-Reptilia 23:487-493 <ResearchGate>

Greene, H. W. 1994. Homology and behavioral repertoires. Pages 369-391 in B. Hall, editor. Homology: The Heirarchical Basis of Comparative Biology. Academic Press, San Diego <Google book>

Greene, H. W. and G. M. Burghardt. 1978. Behavior and phylogeny: constriction in ancient and modern snakes. Science 200:74-77 <abstract>

Hampton, P. M. 2011. Ventral and sub-caudal scale counts are associated with macrohabitat use and tail specialization in viperid snakes. Evolutionary Ecology 25:531-546 <link>

Holm, P. A. 2008. Phylogenetic biology of the burrowing snake tribe Sonorini (Colubridae). PhD dissertation. University of Arizona <full-text>

Jackson, K. and T. H. Fritts. 2004. Dentitional specialisations for durophagy in the Common Wolf snake, Lycodon aulicus capucinus. Amphibia-Reptilia 25:247-254 <full-text>

Loop, M. S. and L. G. Bailey. 1972. The effect of relative prey size on the ingestion behavior of rodent-eating snakes. Psychonomic Science 28:167-169 <full-text>

Marques, O. A. V. and I. Sazima. 2008. Winding to and fro: constriction in the snake Anilius scytale. Herpetological Bulletin 103:29-31 <link>

Martins Teixeria, D., M. Luci Lorini, V. G. Persson, and M. Porto. 1991. Clelia clelia (Mussurana). Feeding behavior. Herpetological Review 22:131-132 <link>

Mehta, R. S. and G. M. Burghardt. 2008. Contextual flexibility: reassessing the effects of prey size and status on prey restraint behaviour of macrostomate snakes. Ethology 114:133-145 <full-text>

Mirtschin, P. J., N. Dunstan, B. Hough, E. Hamilton, S. Klein, J. Lucas, D. Millar, F. Madaras, and T. Nias. 2006. Venom yields from Australian and some other species of snakes. Ecotoxicology 15:531-538 <full-text>

Mori, A. 1991. Effects of prey size and type on prey-handling behavior in Elaphe quadrivirgata. Journal of Herpetology 24:160-166 <link>

Mori, A. and K. Tanaka. 2001. Preliminary observations on chemical preference, antipredator responses, and prey-handling behavior of juvenile Leioheterodon madagascariensis (Colubridae). Current Herpetology 20:39-49 <full-text>

Mushinsky, H. R. 1984. Observations of the feeding habits of the short-tailed snake, Stilosoma extenuatum in captivity. Herpetological Review 15:67-68 <link>

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

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Shine, R. 1977. Habitats, diets, and sympatry in snakes: a study from Australia. Canadian Journal of Zoology 55:1118-1128 <abstract>

Shine, R. and T. Schwaner. 1985. Prey constriction by venomous snakes: a review, and new data on Australian species. Copeia 1985:1067-1071 <link>

Stettler, P. H. 1959. Zur Lebensweise von Dipsas turgidus (Cope), einer schneckenfressenden Schlange. Aquarien und Terrarien 8:238-241.

Vidal, N. and S. B. Hedges. 2002. Higher-level relationships of snakes inferred from four nuclear and mitochondrial genes. Comptes Rendus-Biologies 325:977-985 <link>

Willard, D. E. 1977. Constricting methods of snakes. Copeia 1977:379-382 <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.

What the Provincial Snakes of Canada Should Be

This post will soon be available in Spanish!

In case, like many Americans, you need a map

Happy Canada Day! And indeed there is a lot to celebrate, in particular Canada's new liberal government and the positive effects it has had on science and the environment. Three summers ago, I wrote in two parts (I and II) about what the symbolic snakes of each of the US states should be, inspired by the witty and spot-on post 'The State Birds: What They SHOULD Be' from thebirdist.com. In response to a tweet from Canadian Field Naturalist, a journal that publishes ecology, behaviour, taxonomy, conservation, and other topics relevant to Canadian natural history, and because Canadian provinces also have various representative symbols (none reptilian, except for the feathered kind, which I might add are somewhat better chosen than those of the US states), this summer I decided to cover the US's northern neighbor as well. Does Canada even have any snakes, you might ask? In fact, Canada is home to 27 species of snake, which might surprise those of us who have grown up in regions farther south. That's enough for every province and territory to have two provincial snakes, with one left over, although the uneven geographic distribution of species precludes that, as we'll see. I followed the same "no duplication" rule as I did for the State Snakes, but I allowed snakes that had been used as U.S. State Snakes to be used again, because almost all of the species found in Canada had also been used for a U.S. state. Feel free to chime in with your opinion about what your favorite province's snake should be, if it differs from my choice.

1. Alberta. Prairie Rattlesnake (Crotalus viridis)

Prairie Rattlesnake (Crotalus viridis)

Alberta, well-known for its dinosaurs, also harbors a fairly substantial diversity of modern reptiles for a place with such long winters. Seven species of snake can be found in the province, but perhaps the most quintessential are Prairie Rattlesnakes. Prairie Rattlesnakes in Alberta occur in shortgrass prairies, dry grasslands, and sagebrush in the southeastern part of the province. At the northwestern edge of their range, Prairie Rattlesnakes in Alberta take 5-8 years to reach sexual maturity, and give birth to 4-12 live young, which are quite large (~11" long; compared to ~9" in the more southerly parts of their range). Females may remain with their young for up to 10 days after giving birth. Historically, Prairie Rattlesnakes were found as far west as Calgary and almost as far north as Red Deer, but the species has declined in many areas due to persecution and habitat loss. Venomous snakes are rarely very popular, but provincial symbol-hood might help establish rattlesnakes as wildlife to be valued rather than pests to be exterminated (and Alberta is already quite progressive about protecting its snakes).

2. British Columbia. Sharp-tailed Snake (Contia tenuis)

Sharp-tailed Snake (Contia tenuis)

BC might be my favorite province, principally because of the Nanaimo Bar, a three-layer no-bake dessert created in the eponymous coastal city of Nanaimo. I chose the Sharp-tailed Snake to represent BC because in some ways it resembles a reversed Nanaimo Bar—the dorsal coloration is similar to the graham-cracker-and-almond base, the color of the sides to the vanilla custard center (sort of), and the belly to the delectable chocolate-and-coconut topping. These snakes are found on Vancouver Island, the nearby Gulf Islands, and possibly on the adjacent mainland. These cute little snakes eat slugs, including the infamous banana slugs, which I bet don't taste anywhere near as good as Nanaimo Bars. Descriptions of Sharp-tailed Snakes were first published in 1852 (by herpetologists Spencer Fullerton Baird & Charles Frédéric Girard, who received collections made the decade before in the Puget Sound area), exactly 100 years before the first printed recipes featuring Nanaimo bar ingredients were published in the Women's Auxiliary to the Nanaimo Hospital Cookbook (although I'll admit that's a pretty tenuis connection).

3. Manitoba. Western Hog-nosed Snake (Heterodon nasicus)

Western Hog-nosed Snake (Heterodon nasicus)

Even though Manitoba is very well-known for its Narcisse Gartersnake Dens, it has greater snake diversity than several of the other provinces, for which the gartersnake must be reserved. Some of Manitoba's most interesting snakes are Western Hog-nosed Snakes, which are found in sandy areas in the southwestern part of the province. As with other snakes at the northern limits of their range, they have a short activity season—they mate in May and lay 5-12 eggs in late June or early July, which then hatch by August. A study of Western Hog-nosed Snakes in Spruce Woods Provincial Heritage Park, Manitoba, found that they emerge from their burrows on any day when they could achieve a body temperature of at least 29°C (84°F). Like gartersnakes (though not quite to the same extent), these snakes can achieve fairly high densities in certain areas, so I think they could be good candidates for expanding our knowledge of snake ecology and behavior in the wild into phylogenetically-uncharted territory, challenging the statement made by Rick Shine in 1987 that "It's a good thing you Yanks have garter snakes, or you wouldn't have anything to study."

4. Newfoundland & Labrador. Maritime Gartersnake (Thamnophis sirtalis pallidulus)

Maritime Gartersnake (Thamnophis sirtalis pallidulus)

Newfoundland and Labrador is the only Canadian province without any native snakes. However, in recent years southwestern Newfoundland in the vicinity of St. David's has apparently been colonized by Maritime Gartersnakes, a beautiful subspecies of Common Gartersnake. Although no genetic analyses have been performed, it's likely that this population was founded by individuals shipped across the Gulf of St. Lawrence in hay bales or other cargo from Québec, New Brunswick, Nova Scotia, or Prince Edward Island. A poll by the CBC revealed that 12% of respondents thought that the recent colonization was "actually kind of cool", whereas a discouraging 49% of respondents were "not happy about it at all". It's rumored that gartersnakes were purposefully but unsuccessfully released in the St. John's area in eastern Newfoundland decades ago, either by farmers hoping to control rat populations or by someone who brought them back from the mainland hoping to sell them as pets (though both scenarios are likely more urban legend than fact). A string of recent mild winters may have allowed the gartersnakes in western Newfoundland to persist, but the extent to which climate change will enable a Florida-pythons scenario writ-small in Newfoundland remains to be seen. At the very least, this could be a golden opportunity for snake biologists to study what happens when snakes enter an ecosystem from which they have been absent for thousands of years, a rare event even in an age of snake invasions.

5. New Brunswick. Smooth Greensnake (Opheodrys vernalis)

Smooth Greensnake (Opheodrys vernalis)

Soctsman Andrew Leith Adams was an army physician who served in India, Egypt, and Canada during the 1800s. He spent his spare time studying the natural history of these countries, about which he later wrote several books, including his 1873 Field and forest rambles, with notes and observations on the natural history of eastern Canada. In it, he wrote "The Reptiles of New Brunswick are neither numerous nor formidable.", which, compared with the snake fauna he doubtless experienced in Egypt and India, was certainly true. He mentioned several snake species, in particular noting that "One of our most common fangless snakes is the active little green species (C. vernalis)", using the C. to abbreviate the genus Coluber, which Linnaeus had used for practically all snakes except boas and rattlesnakes. This handsome species has also frequently gone by the binomial Liochlorophis vernalis, among a half-dozen other genera into which it has been placed over the years.

6. Northwest Territories. Red-sided Gartersnake (Thamnophis sirtalis parietalis)

Mating ball of Thamnophis sirtalis parietalis

Red-sided Gartersnakes are the only snakes found in the Northwest Territories, where they achieve high densities near Fort Smith between the southern shore of the Great Slave Lake and Wood Buffalo National Park. Because there are few suitable hibernacula, thousands of individuals share the same den. Long winters and short, cool summers have resulted in a mating system that is unusual among snakes, although it is also possibly the most well-known because it is easily studied. Upon emergence from the in mid-April, snakes spend 2-3 weeks hanging around the entrance, during which time males compete fiercely to mate with females, forming colossal "mating balls". They then migrate over 2.3 miles (3.75 km) to their summer marshland habitat, where they remain until late August, giving birth to litters of young that are relatively small in number (~12 vs. ~19 in Manitboa) and large in body size (191 mm SVL vs. 154 mm in Manitoba). Females in the NWT rarely give birth in two successive years, instead saving up energy from one year in order to reproduce the next. They also mature at larger body sizes (570 mm SVL vs. 527 mm in Manitboa) than snakes further south. I bent the rules a little here since both Newfoundland and the NWT have only T. sirtalis (they have different subspecies, and this species might be split up fairly soon). 

7. Nova Scotia. Ring-necked Snake (Diadophis punctatus)

Brown-morph and normal Diadophis punctatus from Nova Scotia
From Gilhen 2011

Ring-necked Snakes are cute little snakes that mostly eat invertebrates, although they have been known to snack on the occasional salamander. In Nova Scotia, they can be found almost throughout the province, and an unusual brown morph occurs, particularly on Big Tancook Island in Mahone Bay along the east coast. According to the notebooks of Harry Piers, an early 20th century naturalist, museum curator, and historian, ringnecks were known to the native Mi'kmaq People as “the worst snake, Um-taa-kum (k)”, although it's not clear why. One communal nest found under a boulder near McCabe Lake in Halifax County contained 117 eggs, which must have been laid by at last 15, and probably many more, females (clutch size ranges from one to eight).

8. Nunavut. Ellesmere Island erycine (Eocene boa)

Drawing of Ellesmere Island erycine vertebra
Dotted lines show best-guesses at broken-off parts
A. Dorsal and B. right lateral view
From Estes & Hutchison 1980

Unfortunately, there are no living wild snakes in Nunavut. Initially I was going to get around this by writing only about the true provinces, but then I found evidence that a 50-million-year-old fossil snake vertebrae was found on Ellesmere Island, above the Arctic Circle at about 78.5° north (find it here at the awesome new Paleobiology Database Navigator). This vertebra belonged to an undescribed species of boid snake probably related to rubber boas, and it was found in an Eocene fossil deposit that used to be a lush river delta and floodplain, with abundant swamps, alongside pike, bowfin, and gar, mud & softshell turtles, alligators, monitor lizards, giant salamanders, and even primates. The single bone is part of the collection of the Canadian Museum of Nature (specimen number 32403) and hasn't been assigned to a species or even a genus because it's broken. Paleontologists are fairly confident that it is an erycine boid based on comparisons made with a half-dozen other extinct genera that probably belong in this group. Recent phylogenies of booids elevate Erycinae to a family, but do not include extinct taxa, so it's difficult to say for sure how these snakes were related to each other and to living species.

9. Ontario. Eastern Foxsnake (Pantherophis vulpinus)

Eastern Foxsnake (Pantherophis vulpinus)

Ontario has more snake species to choose from than any other province, including seven that are found nowhere else in Canada. At the JMIH meeting in Reno last summer, I posed the question of which one best represented Ontario to herpetologist Jacqueline Litzgus, a native of Ontario and a professor at Laurentian University. She was unhesitant in recommending the Eastern Foxsnake, the only species of snake whose range is mostly in Canada (which perhaps makes it sort of a national snake as well, although the common gartersnake is found in more provinces). Foxsnakes are large constrictors that are closely related to cornsnakes and (slightly less closely) to ratsnakes. They probably recolonized northern North America more quickly after the retreat of the glaciers than most snakes because of their mobility and the flat terrain left behind in the midwest. We once thought that the two species had a disjunct range, with the western foxsnake (formerly P. vulpinus) being found in the USA between the Missouri River and Lake Michigan, separated by a foxsnake-less area in northeastern Indiana and the lower peninsula of Michigan from the eastern foxsnake (formerly P. gloydi), which was found south and east of Lake Huron in Ontario, Michigan, and Ohio. However, a 2011 study used evidence from a single mitochondrial gene to suggest that the Mississippi River seemed to be a more significant genetic barrier and that western foxsnakes east of the Big Muddy in Wisconsin and Illinois were more closely related to eastern foxsnakes than they were to western foxsnakes in Iowa and Minnesota. Because the type specimens for both former foxsnake species were within the eastern lineage, this species became P. vulpinus (the older name), P. gloydi disappeared, and the "new" western foxsnake was named P. ramspotti. Runner up: Massasauga (Sistrurus catenatus), because of the town of Missisauga, Ontario.

10. Prince Edward Island. Red-bellied Snake (Storeria occipitomaculata)

Red-bellied Snake (Storeria occipitomaculata)

Located in the Gulf of St. Lawrence, Prince Edward Island was formed as a sandstone peninsula 250-300 million years ago. The end of the ice age 15,000 years ago and the retreat of the glaciers laid down glacial till and increased the sea level, disconnecting PEI from the mainland. PEI only has three species of snakes, all of which colonized the island within the last 15,000 years. Despite the fact that no lizards or turtles have been able to make the same crossing, PEI is still way ahead of Québec's similarly-sized Île d'Anticosti, which lies ~190 miles (~300 km) to the north and has no native species of amphibians or reptiles. Of the tiny red-bellied snake, PEI naturalist John Mellish wrote in the 1870s "This variety is numerous, is smaller in size, and seems to be less courageous than some of the other species". Although Mellish got this much right, he was as prone to exaggeration as many modern observers, interspersing his species accounts with tales of snakes charming their prey, swallowing their young, and attacking people. In reality, red-bellied snakes mostly attack slugs, and their peculiar lip-curling display is hardly threatening to a human.

11. Québec. Milksnake (Lampropeltis triangulum)

Milksnake (Lampropeltis triangulum)

Québec is best emblematized by the Milksnake, which was first described by a French herpetologist, Bernard Germain de Lacépède, in 1789. Lacépède's two-volume masterpiece, Histoire Naturelle, is a classic work in herpetology. Although Lacépède mostly used French vernacular names,  ("le triangle" for the milksnake, after the double triangles on top of its head), he used Linnaeus's Latin binomial system about 65% of the time in a 59-page table in the third section of the second volume, which covered legless amphibians and reptiles. However, because he was not consistent in his use of Latin binomials, the taxonomic community decided in 1987 that the names in volume two were not valid (volume one, which covers turtles, lizards, and amphibians, contains a 3.5' x 1.75' fold-out table that was consistently binomial, so these names remain valid). Four snake names, including Lampropeltis triangulum, were rescued because of their long history of use. The other three (Agkistrodon piscivorus, Langaha madagascarensis, and Python reticulatus) were much longer-used than L. triangulum, which probably wouldn't have made the cut if not for an earlier decision by the ICZN as part of a case involving the mistaken identity of Linnaeus's scarletsnake (Cemophora coccinea) specimen and the name he gave it, Coluber doliatus, which was mistakenly used for the milksnake for over 150 years. The 1967 case invalidated doliatus and fixed triangulum as the specific epithet of the milksnake, which prevented it from later being invalidated with the rest of Lacépède's snake names. In this way the species is somewhat rebellious (in a nomenclatural sense), which I think would please many Québécois.

12. Saskatchewan. Gophersnake (Pituophis catenifer)

Gophersnake (Pituophis catenifer)

On the first page of one of my favorite novels, Farley Mowat's Owls in the Family, the author describes growing up in Saskatoon, Saskatchewan: "When you stepped off the end of the Railroad Bridge you stepped right onto the prairie and there you were—free as the gophers. Gophers were the commonest thing on the prairie. The little mounds of yellow dirt around their burrows were so thick, sometimes, it looked as if the fields had yellow measles." Although I like owls, these days I more often have another gopher predator in mind—the eponymous gophersnake (Pituophis catenifer), also less-aptly known as the bullsnake. These harmless creatures are often mistaken for rattlesnakes, because they have a superficially similar pattern (and they do rattle their tails, although they have no specialized noise-making structure). Confusion over the common name led Edward Abbey or one of his editors to include the scientific name of the eastern indigo snake (aka the blue gophersnake), Drymarchon corais couperi, for the bullsnake in the essay 'The Serpents of Paradise' in the 1968 edition of Desert Solitaire (although it is correct in 1988 edition).

13. Yukon. ?

I hope they find a snake

The Yukon Territory has no living snakes and no snake fossils (yet). This is actually quite ironic, because most living North American snakes crossed into our continent from Asia over the Bering Land Bridge, and some of them almost certainly slithered through what is today the Yukon. It is possible that somewhere in the southern Yukon exists a population of gartersnakes, which are found in the southern NWT and also possibly in the Alaskan panhandle. Three reliable sight records and one specimen (now lost) from remote areas along Taku & Stikine Rivers in Alaska give us hope, although unfortunately neither basin enters the Yukon. Other snake sightings of snakes from Alaska include odd T. sirtalis and T. ordinoides specimens from more urban areas, which almost certainly represent translocations (genetic evidence supports this in at least one case). T. sirtalis are found just 200 miles (320 km) south of the Yukon border in BC. It isn't completely crazy to imagine snakes living at such northerly latitudes; European Adders (Vipera berus) are found above the Arctic Circle in Scandinavia. If nothing else, gartersnakes from British Columbia will probably disperse there eventually if climate change keeps up with predictions.

ACKNOWLEDGMENTS

Thanks to Ben Lowe, David O'Connor, JD Willson, Todd Pierson, Andy Teucher, Michael, Gary Nafis, and Nick Scobel for the use of their photos, to Jackie Litzgus for helping me make the decision about Ontario, and to Gareth Hopkins for introducing me to Nanaimo bars.

REFERENCES

Manitoba Thamnophis on the side of a U-Haul truck

Anonymous. 1987. Opinion 1463. De Lacépède, 1788-1789, Histoire Naturelle des Serpens and later editions: rejected as a non-binominal work. Bulletin of Zoological Nomenclature 44:265-267 <link>

Baird, S.F. and C. Girard. 1852. Descriptions of new species of reptiles, collected by the U.S. exploring expedition under the command of Capt. Charles Wilkes, U.S.N. First part. - Including the species from the Western coast of America. Proceedings of the Academy of Natural Sciences of Philadelphia 6:174-177 <link>

Brongersma, L.D. 1972. On the “Histoire naturelle des Serpens” by de la Cépède, 1789 and 1790, with a request to reject this work as a whole, and with proposals to place seven names of snakes, being nomina oblita, on the Official index of rejected and invalid names in zoology, and to place three names of snakes on the Official list of specific names in zoology (Class Reptilia). Bulletin of Zoological Nomenclature 29:44-61 <link>

Crother, B.I., M.E. White, J.M. Savage, M.E. Eckstut, M.R. Graham, and D.W. Gardner. 2011. A reevaluation of the status of the Foxsnakes Pantherophis gloydi Conant and P. vulpinus Baird and Girard (Lepidosauria). ISRN Zoology 2011 <link>

Estes R, Howard Hutchison J, 1980. Eocene lower vertebrates from Ellesmere Island, Canadian Arctic Archipelago. Palaeogeography, Palaeoclimatology, Palaeoecology 30:325-347 <link>

Gilhen, J. 2011. The Brown Morph of the Northern Ringneck Snake, Diadophis punctatus edwardsii, on Big Tancook Island, Mahone Bay, Nova Scotia. The Canadian Field-Naturalist 125:69-71  <link>

Hodge, R.P. 1976. Amphibians and Reptiles in Alaska, the Yukon, and Northwest Territories. Alaska Northwest Pub. Co.

Larsen KW, Gregory PT, Antoniak R, 1993. Reproductive ecology of the Common Garter Snake Thamnophis sirtalis at the northern limit of its range. American Midland Naturalist 129:336-345 <link>

Leavesley, L.K. 1987. Natural history and thermal relations of the Western Hognose Snake (Heterodon nasicus nasicus) in southwestern Manitoba. MS thesis. University of Manitoba, Winnipeg, Manitoba.

Rossman, D.A., N.B. Ford, and R.A. Seigel. 1996. The Garter Snakes: Evolution and Ecology. University of Oklahoma Press, Norman, Oklahoma. (Shine quote opens chapter 4, page 55)

West, R.M., M.R. Dawson, and J.H. Hutchison. 1977. Fossils from the Paleogene Eureka Sound Formation, N.W.T., Canada; occurrence, climatic and paleogeographic implications. Milwaukee Public Museum Contributions in Biology and Geology 2:77-93.

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