Basics of snake skulls

This article will soon be available in Spanish!

Snakes have a lot more bones than we do, but they have a lot fewer types of bones. Aside from a few boas, pythons, pipesnakes, and blindsnakes with vestigial femurs, most snakes just have a few hundred vertebrae with one pair of ribs each (except in the neck & tail), and a skull.

The snake skull is a remarkable structure. Snake skulls are highly kinetic, with a lot more moving parts than our skulls. Human skulls have just one movable part: the temporomandibular joint, which opens and closes your mouth. Snake skulls have many joints and moving parts; they can move the left and right sides of their jaws independently, as well as the outer (maxilla) and inner (palatine+pterygoid) parts of their upper jaws. Many bones that are tightly knit together in the skulls of most animals are loosely connected by stretchy ligaments in snakes, allowing them to stretch their jaws over huge prey (pardon the goofy music in the linked video). Contrary to the popular phrase, snakes cannot actually "unhinge" their jaws (Harry Greene explains this very well in this video).

The right side of the skull of an alethinophidian snake (nose pointing to the right).
Bones with teeth are the maxilla (mx), palatine (pal), pterygoid (pt), and dentary (d).
From Cundall & Irish 2008. For a key to all abbreviations, click here.
The bones or parts of bones that are shaded are not present in all snake species.

Most snakes have teeth on four pairs of bones, two of which are the same as pairs of bones where humans do: the maxilla (most of our upper jaw) and the dentary (our lower jaw). In addition, almost all snakes have teeth on two bones that in humans form part of the roof of the mouth: the palatine and the pterygoid¹, which are connected one in front of the other. This means that snakes have two upper jaws on each side: an outer one (the maxilla) and an inner one (the palatine+pterygoid). If a snake has fangs, they are always on the maxilla². Some snakes, such as pythons, also have teeth on the premaxilla, where we humans have our incisors, although in most snakes the premaxilla is a part of the snout, has no teeth, and does not act as part of the jaws.

The right half of the skull of a snake, looking up from the bottom (nose pointing to the right).
Bones with teeth are the maxilla (mx), palatine (pal), pterygoid (pt), and dentary (d). The premaxilla (pmx) has no teeth.
From Cundall & Irish 2008. For a key to all abbreviations, click here.The bones or parts of bones that are shaded are not present in all snake species.

Tooth marks left by a
python bite (upper jaw
above, lower jaw below).

You can sometimes see this pattern of tooth marks left behind when a non-venomous snake lets go after biting something, and in fact many resources suggest that you can use the tooth pattern to determine³ whether or not a bite has come from a venomous snake (a viper at least, which are responsible for >99% of venomous snakebites in the USA), since most dangerously venomous snakes have different tooth patterns on account of their fangs, and most of their non-fang teeth don't usually come into contact with the target. I mentioned above that fangs are always on the maxilla, and that's because the maxilla is the primary prey-catching bone in the snake skull. As far as we know, fangs evolved only once, as enlarged teeth at the back of the maxilla in the ancestor of all living colubroid snakes about 75 million years ago. In many living species of snakes, this is still the situation, and the vast majority of these are not dangerous to humans (although some can inflict painful bites if allowed to chew for a few minutes, and a few can be deadly). In at least three cases (vipers, elapids, and atractaspidids), the fangs have moved up to the front of the maxilla, through the developmental suppression of the front part of the maxilla (and its teeth) in the snake embryo. I covered this and the evolution of grooved and hollow fangs in more detail in my article about snake fangs.

The right half of the skull of a snake, looking down from the top (nose pointing to the right).
No teeth are visible. From Cundall & Irish 2008. For a key to all abbreviations, click here.The bones or parts of bones that are shaded are not present in all snake species.

Although most people are most interested in the teeth and fangs, the rest of the snake skull is no less fascinating. The outer and inner upper jaw are connected by a toothless upper jaw bone called the ectopterygoid, which works like a lever to transfer muscular power from the muscles attached to the pterygoid out to the maxilla, which has no muscles of its own. When a snake is eating, the entire upper jaw (inner and outer parts) is raised and moved slightly backward, alternating the left and right sides and pulling the prey into the mouth: the characteristic "jaw-walking" or "pterygoid walk" motion of feeding snakes. So, the front of the pterygoid is attached to the back of the palatine, the ectopterygoid hangs off the outside of the pterygoid, and the maxilla hangs off of the other end of the ectopterygoid. In vipers, whose fangs fold, the maxilla and its fang are pushed forward by the ectopterygoid and pterygoid.

Roughly the same fang movements are made during striking and swallowing. Supratemporal (st), quadrate (q), mandible (ma), pterygoid (pt), ectopterygoid (ec), palatine (pa), prefrontal (pf), maxilla (mx). From Kardong 1977

The independent left and right movement
of the upper jaws of a viper.
Abbreviations as above. From Kardong 1977.

Amazingly, in most snakes there is no direct connection between the upper jaws and the braincase⁴. Instead, the palatine and maxilla are connected to the braincase by long ligaments, which give them great freedom of motion. The front end of the palatine is connected more firmly to the snout, albeit still with some freedom to move. The rear end of the maxilla is also connected by a ligament to the lower jaw. It's really the movements of the palatine and pterygoid that swallow the prey. The lower jaws mainly press the prey against the upper jaws, and the teeth on the dentary and maxilla rarely contact the prey and play little active role in swallowing.

The lower jaws or mandible participate in the process of feeding as well, and unlike in humans they have a loose attachment of the lower jaws to each other at the front of the dentary bones. The dentary bones are connected firmly at the back to the articular bones, which are connected to the quadrate bones at a flexible joint, which are connected to the back of the braincase by the supratemporal bones, also at a somewhat moveable joint. Together with the flexible palato-maxillary apparatus ("upper jaws"), this three-part lower jaw allows snakes to open their mouths very wide, walk their heads over, and consume things that are as big as they are without breaking them into smaller pieces or using their non-existent hands. The quadrate also attaches to the columella, which is the sole inner ear bone in reptiles; thus, the lower jaw also conducts sound to the ear.

So there you have it. The snake skull is divided into four functional units: the braincase, the snout, the palato-maxillary apparatus ("upper jaws") and the mandibular apparatus ("lower jaws"), each of which can move independently (well, except for the braincase, which is relatively stationary). The upper jaws are divided into two partially separated structural-functional units, a medial swallowing unit and a lateral prey capture unit, both of which work with the lower jaws to accomplish their tasks.

From Frazzetta 1970. Click for larger size.

A quick note about a special case: one of my favorite snakes, and one of the first I wrote about on this blog, Casarea dussumeri, are often called Round Island boas, although I chose to use the more apt "splitjaw snakes" in my article. As if the usual kinesis of the snake skull isn't enough, these snakes have a maxilla that is uniquely subdivided into two movable parts, called the anterior and posterior maxilla. The anterior maxilla has 10 teeth and the posterior maxilla has 12. It is thought that the divided maxilla evolved through incomplete development, because the maxilla of other snakes forms in two parts before fusing together in the embryo, and the function is thought to be to help Casarea encircle hard, cylindrical prey such as skinks.

We still have a lot left to learn about snake skulls. We didn't even cover half of the bones in this article. You don't actually so much find snake skulls as you do carefully prepare them. The individual bones are so small and light and fragile that they tend not to fossilize well, nor can they easily be found among the other bones of a snake's skeleton. Even normal cleaning and preparation methods can damage the fragile bones of tiny snake skulls. Thus, there is much left to discover about how they work!

Skull of Natrix natrix from Andjelković et al. 2017. Mobile connections marked with red dashed arrows and circles.Paired bones are shown in yellow (pa – palatine, pt – pterygoid, ec – ectopterygoid, mx – maxilla, st – supratemporal,q – quadrate, cp – compound bone, d – dentary, pf – prefrontal), unpaired bones are shown in green or grey (pmx – premaxilla, na – nasal, b – braincase, smx – septomaxillae & vomers).

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1 Although the pterygoids are stand-alone bones in the roof of the mouth of many vertebrates, in humans they are called the pterygoid processes of the sphenoid bone because they are fused to the sphenoid bone.^↩

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2 There is one very strange snake, Pythonodipsas carinata from Africa, that has an ungrooved fang on the palatine bone. They aren't any studies of their functional morphology so we don't really know exactly how they use their palatine fangs, but they use constriction to subdue their prey.^↩

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3 I don't necessarily recommend this, partly because if you've been bitten then it's too late, and partly because it's better just to learn the few venomous snake species that live in your area than it is to try to follow some "rule" that inevitably has exceptions.^↩

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4 Atractaspidids have a ball-and-socket joint between the prefrontal (part of the braincase) and the maxilla, which along with a gap, bridged by a ligament, between the pterygoid and palatine, allows them to "strike" with their fang backwards, with a closed mouth, using just the fang on one side, a useful if terrifying adaptation for envenomating prey in underground burrows. A hook-like ridge on the fang increases the size of the wound, presumably enhancing the absorption of venom.^↩

ACKNOWLEDGMENTS

Thanks to gibby for the use of their photograph.

REFERENCES

Albright, R. G. and E. M. Nelson. 1959. Cranial kinetics of the generalized colubrid snake Elaphe obsoleta quadrivittata. I. Descriptive morphology. Journal of Morphology 105:193-239.

Albright, R. G. and E. M. Nelson. 1959. Cranial kinetics of the generalized colubrid snake Elaphe obsoleta quadrivittata. II. Functional morphology. Journal of Morphology 105:241-291.

Andjelković, M., Tomović, L., & Ivanović, A. 2017. Morphological integration of the kinetic skull in Natrix snakes. Journal of Zoology, 303:188-198 <link>

Cundall, D. 1983. Activity of head muscles during feeding by snakes: a comparative study. American Zoologist 23:383-396.

Cundall, D. and H. W. Greene. 2000. Feeding in snakes. Pages 293–333 in K. Schwenk, editor. Feeding: Form, Function, and Evolution in Tetrapod Vertebrates. Academic Press, San Diego, CA.

Cundall, D. and F. Irish. 2008. The snake skull. Pages 349-692 in C. Gans, A. S. Gaunt, and K. Adler, editors. Biology of the Reptilia. Volume 20, Morphology H. The Skull of Lepidosauria. The University Of Chicago Press, Chicago, Illinois, USA <link>

Frazzetta. T. 1970. From hopeful monsters to bolyerine snakes? The American Naturalist 104:55-72 <link>

Frazzetta, T. 1971. Notes upon the jaw musculature of the Bolyerine snake, Casarea dussumieri. Journal of Herpetology 5:61-63

Irish, F. and P. Alberch. 1989. Heterochrony in the evolution of bolyeriid snakes. Fortschritte der Zoolologie 35:205.

Juckett, G. and J. G. Hancox. 2002. Venomous snakebites in the United States: management review and update. American Family Physician 65:1367-1375 <link>

Kardong, K. 1974. Kinesis of the jaw apparatus during the strike in the cottonmouth snake, Agkistrodon piscivorus. Forma et functio 7:327-354.

Kardong, K. V. 1977. Kinesis of the jaw apparatus during swallowing in the cottonmouth snake, Agkistrodon piscivorus. Copeia 1977:338-348 <link>

Lombard, R. E., H. Marx, and G. B. Rabb. 1986. Morphometrics of the ectopterygoid in advanced snakes (Colubroidea): a concordance of shape and phylogeny. Biological Journal of the Linnean Society 27:133-164 <link>

Maisano, J. A. and O. Rieppel. 2007. The skull of the Round Island boa, Casarea dussumieri Schlegel, based on high-resolution X-ray computed tomography. Journal of Morphology 268:371-384 <abstract>

Raynaud, A. 1985. Development of Limbs and Embryonic Limb Reduction. Pages 59-148 in C. Gans and F. Billett, editors. Biology of the Reptilia. Volume 15. Development B. John Wiley & Sons, New York <link>

Rieppel, O. 2012. “Regressed” Macrostomatan Snakes. Fieldiana Life and Earth Sciences 5:99-103 <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.

How many snakes are venomous and how many are constrictors?

Click here to read this post in Spanish
Haga clic aquí para leer esta publicación en español

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.^↩

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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>

Penning, D. A. and B. R. Moon. 2017. The king of snakes: performance and morphology of intraguild predators (Lampropeltis) and their prey (Pantherophis). The Journal of Experimental Biology 220:1154 <link>

Rossi, J. V. and R. Rossi. 1993. Notes on the captive maintenance and feeding behavior of a juvenile short-tailed snake (Stilosoma extenuatum). Herpetological Review 24:100-101 <link>

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

Sazima, I. 1989. Feeding behavior of the snail-eating snake, Dipsas indica. Journal of Herpetology 23:464-468 <link>

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.

Snakebite, antivenom research, and basic science

Click here to read in Spanish
Haga clic aquí para leer en español

In the past few weeks, a peculiar congruence of several seemingly-unrelated events took place. (At least) two new scientific papers about snake biology were published, a new video series was announced, some scientists entered contests, and the U.S. executive branch announced a budget proposal with deep cuts to science funding. However, these events aren't as unrelated at they might seem at first glance, and they have something to tell us about where snake biology, and science in general, are going in the future.

The science: part I (puff adders)

A puff adder (Bitis arietans)

Puff Adders (Bitis arietans) are among Africa's most widespread vipers. They are heavy-bodied snakes that are found in savannas and open woodlands. Like most vipers, they eat mostly rodents as adults, which they ambush from carefully-selected sites, which they sometimes occupy for weeks at a time. Recently, Xavier Glaudas and Graham Alexander published a new study showing that, even though Puff Adder strikes last less than two seconds, they can choose to either hold onto or let go of the prey depending on its size. Specifically, they hold onto small mice, shrews, birds, toads, and lizards, but strike & release larger rodents and rabbits, because retaliatory rat bites are dangerous to them. After they let go of these larger prey, which usually run off a short distance before the venom kills them, they track them down again using stereotypic strike-induced chemosensory searching behavior to locate the scent of non-toxic components of their own venom. This is really similar to findings by Bree Putman and Rulon Clark that Southern Pacific Rattlesnakes (Crotalus oreganus) were more likely to hold onto smaller rodents than to larger ground squirrels. You can watch 26 awesome videos selected from an archive of thousands of hours of video taken in the wild over more than two years.¹

This research matters because venomous snakes and their prey are in constant evolutionary arms races, leading to:

1. a mosaic of new biochemical compounds that are often useful in treating disease
2. a mosaic of new biochemical compounds that can make venomous snakebite really hard to treat

We'll come back to the second one in a minute. The obvious importance of human medicine and venomous snakebite treatment overshadow a third important reason to study snakes and what they eat. Although the beneficial role of snakes in rodent control is taken as gospel by many advocates of snake conservation, the amount of data that we actually have on what snakes eat in the wild is surprisingly small. For many species, we don't even have a general idea of what kinds of prey they like to eat. Given recent estimates that spiders eat about as much meat as people do worldwide, and the potential for snakes to reach very high population densities in certain habitats, it's likely that the top-down effects of snakes as predators are significant ecosystem services that most humans aren't aware of and thus undervalue. Indirect effects on other aspects of the ecology of snake prey species, such as predation release and disease transmission, link snake predation even more strongly to human health. This is particularly timely in light of recent predictions that 2017 will be a big year for white-footed mice and thus for Lyme disease in the northeastern USA, controversy over the reintroduction of Timber Rattlesnakes, one of the white-footed mouse's top predators, to Quabbin Island in Massachusetts², and the continuation of both the infamous Sweetwater Rattlesnake Roundup³ and the reformed Claxton Wildlife Festival and Lone Star Rattlesnake Days earlier this month.

The science: part II (how cobras got their flesh-eating venoms)

A Mozambique spitting cobra (Naja mossambica) spitting its venom

Spitting cobras are even more well-known than puff adders because of their defensive venom spitting abilities, showcased on the BBC's Life in Cold Blood. They are found in Africa and Asia and are thought to have evolved two or three times from non-spitting cobras. A new paper from the lab of Bryan Fry at the University of Queensland sheds some light on when and why venom spitting evolved. Elapid snakes, including cobras, have venoms rich in neurotoxins, which are highly potent toxins that are very effective at paralyzing their prey. Cobras also have less potent cytotoxins that kill cells directly, which is a bit weird. What is the function of these toxins?

Toxicity of snake venom to human cells grown in culture.
Warm colors indicate higher toxicity.
From Panagides et al. 2017

The hypothesis put forth here is that the first step towards venom spitting was the evolution of hooding behavior and morphology, which happened twice in elapids: once in "regular" cobras and once in King Cobras, which are more closely related to mambas. Only once a conspicuous visual display was present was there selective pressure for cytotoxic venom components delivered to the eyes of potential predators via spitting. Although the venom of both groups is cytotoxic, Hemachatus (rinkhals) and Naja cobras use three-finger toxins, whereas King Cobras use L-amino acid oxidase enzymes, consistent with the undirected, opportunistic nature of our current model of venom evolution by gene duplication and mutation. The authors suggest that further elevations in cytotoxicity are linked to bright bands and other aposematic colors or hood markings, although their paper did not attempt to quantify these attributes of cobra displays, which can be quite diverse even within species. Further evidence in support of the hypothesis is that Naja naja and Naja oxiana seem, based on their nested position, to have lost spitting but to have retained cytotoxicity, and their close relatives Naja atra and Naja kaouthia might represent steps down this evolutionary path, being capable of spitting only in some populations and with less accuracy than the African and southeast Asian clades of true spitting cobras.

This is an extremely cool and popular topic. It was covered by IFLS, The Wire, Gizmodo, and the Washington Post. It goes to show that people worldwide are fascinated by venomous snakes, and the Fry lab has done a great job capitalizing on that interest (among other accolades, Fry's graduate student Jordan Debono recently won the Queensland Women in Science Peoples' Choice Award [a contest that was decided by an online popular vote; more on this later] for her research on global snakebite treatments). One reason for this fascination has to do with the question of who, exactly, these cobras are defending themselves from? The most reasonable hypothesis, given the timing and geography of the diversification of spitting cobras and the precision with which they can target forward-facing eyes and hominoid faces, is primates. Us, and our ancestors, who have eaten and been eaten by snakes for millions of years. Studying spitting cobras is a window into our own evolutionary past, a way for us to learn about ourselves. But, let us not be misled into thinking that interactions between humans and cobras are a thing of the past.

The upshot: the truth about snakebite

You can follow the ASV @Venimologie

If you haven't read the blog by medical toxinologist Leslie Boyer, you really should. Earlier this month she wrote about the vicious circle of antivenom shortage in sub-Saharan Africa, where millions of people are bitten by venomous snakes every year, many of which die or suffer awful injuries because they lack access to good antivenom. This crisis has prompted the creation of the African Society of Venimology and a new series of snakebite training videos in English, French, and Spanish. The politics and economics of antivenom are complicated and reflect larger issues in medicine, education, quality control, supply and demand, and how global economics and corporations have failed to respond to the needs of local communities and consumers. In a nutshell, the issue is that antivenom manufacturers don't make enough good antivenom, because not enough people buy it. People don't buy it because it's expensive, and it's expensive because not that much is made. This is despite a huge need for it—but not everybody with a snakebite goes to a hospital and gets antivenom in Africa, partially because it's not certain there will be any and partially because a lot of patients and doctors don't know about antivenom, because it's not in widespread use (which is mostly because of the reasons above). Other exacerbating problems include that it's often not certified, fake products can price the real antivenom out of the market, and the infrastructure for distributing antivenom and information in Africa is sub-optimal (but improving). Fixing any one or even most of these problems won't fix the whole system—if any one of them break down, supply and demand will be out of balance and people won't get the care they need.

A lot of the same issues used to be present in Mexico, but product improvements, government outreach, and massive education efforts in the 1980s and 1990s dramatically reduced mortality from venomous snakebite and led Mexico to become a major producer and consumer of high-quality, affordable antivenom, so much so that the USA now imports some of these drugs from Mexico. The Mexican government enabled the Mexican antivenom industry to be competitive and reach its market, which is much larger than the domestic market for American antivenom manufacturers—medically-serious venomous snakebites (and scorpion stings) in the USA are mostly confined to the southwest, and the per-capita risk of snakebite is the lowest in the world. This creates its own unique problems. You may have heard about the controversy surrounding the discontinued coralsnake antivenom made by Wyeth, and there are compelling arguments that the Mexican polyvalent antivenoms Anavip (made by Bioclon for humans) and ViperSTAT (made by Veteria Labs for cats and dogs) are more effective and much less expensive (although this is due almost exclusively to the idiosyncrasies of the US healthcare finance system) than the only FDA-approved viper antivenom, CroFab (although BTG, the maker of CroFab, filed a complaint asserting that these Mexican products infringe on its patent).

Finally, the global importance of the availability of high-quality, affordable antivenom for Latin American, African, and other exotic snakes is only going to increase as venomous snakes become more popular as pets and in zoos. This is particularly true in parts of the world completely lacking venomous snakes or with only very benign, non-life-threatening species, such as northern Europe, Scandinavia and northern North America, where doctors may be totally unprepared for a snakebite emergency and may not have appropriate antivenom on hand. This is exactly the kind of situation where government funding, in the form of orphan disease R&D grants, could play a role in making it affordable for researchers and doctors to save lives.

For a great introduction to and more in-depth coverage of these issues, you should watch The Venom Interviews or read their coverage of the recent video series.

The future: sequence the Temple Pitviper genome

Temple or Wagler's Pitvipers (Tropidolaemus wagleri)
at the famous Temple of the Azure Cloud in Penang, Malaysia
You can vote to sequence their genome here!

Genomics of snakes is taking off in a big way, and we stand to learn a lot more about the evolution and function of snake venoms and the treatment of their effects. But, funding for basic science isn't a priority for many people, and more and more scientists are turning to crowd-funding their research or relying on limited funding from private foundations, which often decide which projects to fund through a crowd-sourced voting process. This isn't necessarily a bad thing; in fact, I think it's a great thing in many cases. But, it's important to realize that government funding for science is different from private funding in two crucial ways: 1) there is a lot more of it (at least for now), and 2) it's not driven by specific, private interests. A great example is the Orianne Society, a non-profit reptile conservation organization whose founding purpose was preventing the extinction of Eastern Indigo Snakes (Drymarchon couperi). Thanks to generous donations from private funding sources, the Society succeeded in purchasing large areas of critical habitat for this endangered snake and protecting them in perpetuity, probably the most effective and laudable conservation goal in existence. Another good example is the work of the Durrell Wildlife Conservation Trust, who have essentially saved a globally-rare snake, Casarea dussumieri, from extinction in the wild. I wish the quality conservation work that these organizations have become well-known for were more common, but to date their donors are some of the only large private backers of reptile research and conservation in the world.

Snakes are part of human economics, albeit to a lesser extent than many insects, fishes, birds, and mammals—they are hunted for food (although there are many issues surrounding better management of unsustainable harvests), kept as pets, their skins made into leather, and their venom harvested to make antivenom and other drugs. But, in their current form, these industries place very little emphasis on finding out more about snake biology in the wild; it just isn't necessary for them to make a profit, even though the information is important for what they do. Antivenom manufacturers are accountable to their shareholders, but trying to block FDA approval of Mexican antivenom is certainly not going to result in better treatment for snakebite victims in the USA, and American companies aren't investing in any research to create new, better products themselves, since drug development is expensive and risky, and they already have a monopoly on antivenom in the USA.

It's no secret that snakes and snake research have a PR problem: even scientific journals are less likely to publish research articles about snakes than about mammals and birds (although the bias is likely subliminal). Many people prefer cute fuzzy animals that are similar to humans, but research into the biology of un-fuzzy animals is equally important. There's a parallel to the divide between funding for basic and applied science. Basic science isn't usually as sexy as the exciting, fun applications that come later, like saving lives, curing diseases, or discovering new complex biological phenomena. However, important applied science like antivenom creation cannot happen without basic science, in particular basic science on snakes. Private companies can't afford to invest in basic science the way they once did. Which leaves government funding and that from a limited number of interested, private backers.

We should support public funding for science and elect politicians who will do the same; better treatment for snakebite should be the least partisan and most universally-agreed-upon goal in the world. I think the path between basic (snake ecology, venomics, and genomics) and applied (antivenom manufacturing and public health) science is shorter and clearer in this context than in many, but the same principles apply—you cannot have medicine, conservation, and the other good parts of civilization without science.

You can vote now through April 5th 2017 for a project sequencing the entire genome of the Temple Pitviper (Tropidolaemus wagleri) co-led by Ryan McCleary.

Stay tuned for more about the role of snake venom proteins in treating human diseases, and the role of snakes as predators in ecosystems.

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1 Naturally, I wanted to link to the full-text of the paper so that anyone interested in learning more could read it, but the publisher (Wiley) has a 12-month embargo on posting the PDF anywhere online. They actually expect you to pay between $6 and $38 to read the article. Now, I think it's great research, and it probably cost Glaudas, Alexander, and their university thousands of dollars and thousands of hours to do it. But, if you pay Wiley to read their paper, none of that money will go to them, nor to the scientists who peer-reviewed their work for free. It will go to Wiley, who Xav paid (maybe) to publish. They could have paid $3,000 to make it open access, but you can understand why they didn't. No wonder most most science is read by fewer than 10 people. It's an outdated model that can't go away fast enough. In contrast, the spitting cobra paper is open access, which cost its authors over $1,500. This is typical; academic authors almost always lose money on a publication.^↩

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2 Recent update here; you can write the governor of Massachusetts here.^↩

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3 Reports suggest that this year, like last year, a much larger number of live rattlesnakes were collected than markets could support, and at least one person died from a snakebite sustained while trying to capture a rattlesnake for a roundup.^↩

ACKNOWLEDGMENTS

Thanks to Bryan Fry for alerting me in advance of his publication, and to Colin Donahue, Markus Oulehla, and Ian Glover for the use of their photos.

REFERENCES

Bonnet, X., R. Shine, and O. Lourdais. 2002. Taxonomic chauvinism. Trends in Ecology & Evolution 17:1-3 <link>

Boyer, L. V. 2016. On 1000-Fold Pharmaceutical Price Markups and Why Drugs Cost More in the United States than in Mexico. The American Journal of Medicine 128:1265-1267 <full-text>

Boyer, L. V. and A.-M. Ruha. 2016. Pitviper Envenomation Guidelines Should Address Choice Between FDA-approved Treatments for Cases at Risk of Late Coagulopathy. Wilderness and Environmental Medicine. 27:341–342 <full-text>

Boyer, L. V., P. B. Chase, J. A. Degan, G. Figge, A. Buelna-Romero, C. Luchetti, and A. Alagón. 2013. Subacute coagulopathy in a randomized, comparative trial of Fab and F (ab′) 2 antivenoms. Toxicon 74:101-108 <full-text>

Cao, N. V., N. T. Tao, A. Moore, A. Montoya, A. Rasmussen, K. Broad, H. Voris, and Z. Takacs. 2014. Sea snake harvest in the Gulf of Thailand. Conservation Biology 28:1677-1687 <full-text>

Chew, M., A. Guttormsen, C. Metzsch, and J. Jahr. 2003. Exotic snake bite: a challenge for the Scandinavian anesthesiologist? Acta Anaesthesiologica Scandinavica 47:226-229 <full-text>

Chippaux, J.-P. 2012. Epidemiology of snakebites in Europe: a systematic review of the literature. Toxicon 59:86-99 <full-text>

Glaudas, X., T. C. Kearney, and G. J. Alexander. 2017. To hold or not to hold? The effects of prey type and size on the predatory strategy of a venomous snake. Journal of Zoology 10.1111/jzo.12450 <abstract>

Glaudas, X. and G. Alexander. 2017. Food supplementation affects the foraging ecology of a low-energy, ambush-foraging snake. Behavioral Ecology and Sociobiology 71:5 <link>

Margres, M. J., J. J. McGivern, M. Seavy, K. P. Wray, J. Facente, and D. R. Rokyta. 2015. Contrasting modes and tempos of venom expression evolution in two snake species. Genetics 199:165-176 <full-text>

McCleary, R. J. and R. M. Kini. 2013. Non-enzymatic proteins from snake venoms: a gold mine of pharmacological tools and drug leads. Toxicon 62:56-74 <full-text>

Natusch, D. J. D., J. A. Lyons, Mumpuni, A. Riyanto, S. Khadiejah, N. Mustapha, Badiah, and S. Ratnaningsih. 2016. Sustainable Management of the Trade in Reticulated Python Skins in Indonesia and Malaysia. IUCN, Gland, Switzerland <full-text>

Nyffeler, M. and K. Birkhofer. 2017. An estimated 400–800 million tons of prey are annually killed by the global spider community. The Science of Nature 104:30 <full-text>

Panagides, N., Timothy N. Jackson, R. Pretzler, M. P. Ikonomopoulou, Kevin Arbuckle, D. C. Yang, S. A. Ali, I. Koludarov, J. Dobson, B. Sanker, A. Asselin, R. C. Santana, I. Hendrikx, Harold van der Ploeg, J. Tai-A-Pin, R. v. d. Bergh, H. M. I. Kerkkamp, F. J. Vonk, A. Naude, M. Strydom, L. Jacobsz, N. Dunstan, M. Jaeger, W. C. Hodgson, J. Miles, and Bryan G. Fry. 2017. How the cobra got its flesh-eating venom: cytotoxicity as a defensive innovation and its co-evolution with hooding and spitting. Toxins 9 <full-text>

Putman, B. J., M. A. Barbour, and R. W. Clark. 2016. The foraging behavior of free-ranging Rattlesnakes (Crotalus oreganus) in California Ground Squirrel (Otospermophilus beecheyi) colonies. Herpetologica 72:55-63 <full-text>

Stock, R. P., A. Massougbodji, A. Alagon, and J.-P. Chippaux. 2007. Bringing antivenoms to Sub-Saharan Africa. Nature Biotechnology 25:173-177 <full-text>

Wade, L. 2014. For Mexican antivenom maker, US market is a snake pit. Science 343:16-17 <full-text>

Willson, J. D. 2016. Indirect effects of invasive Burmese pythons on ecosystems in southern Florida. Journal of Applied Ecology 10.1111/1365-2664.12844 <full-text>

Willson, J. D. and C. T. Winne. 2016. Evaluating the functional importance of secretive species: A case study of aquatic snake predators in isolated wetlands. Journal of Zoology 298:266-273 <full-text>

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