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Friday, October 30, 2015

Are there any countries without snakes?

This post will soon be available in Spanish
Este post estará pronto disponible en español

Global distribution of all snake species combined
Public domain from Wikipedia
Terrestrial data from Ernst & Ernst (2011) and Cogger et al. (1998)
Sea snake data based on Campbell & Lamar (2004), Phillips (2002),
Ernst & Ernst (2011), and Spawls & Branch (1995)
Snakes are found in almost every country in the world, but there are a few places without wild1 snakes. Snake-free land generally falls into two categories: remote islands, mostly formed by volcanism or as atolls, that have never been part of a continental land mass and/or have been isolated from continents for a long time, and continental areas that are or were covered by ice within the last 26,000 years and haven't been recolonized since (for example, there are snake fossils from northern Canada, where no snakes live now, from a time when it was much warmer). There are also snake-free parts of the oceans, and probably there are some urban areas that are so disturbed that no snakes live there any more (e.g., downtown Manhattan), although they once did.


Iceland is a volcanic archipelago just outside the Arctic Circle. Despite its high latitude, Iceland is warmed by the Gulf Stream and has a temperate climate, so snakes might actually do fairly well there, especially if they could take advantage of its plentiful geothermal features, as the high-altitude hot-spring snakes of Tibet (genus Thermophis) have done. However, Iceland has never been connected to any continent—instead, it was formed about 20 million years ago by a series of volcanic eruptions in the Mid-Atlantic Ridge, which separates the Eurasian and North American plates. It's been at about its current latitude the entire time, and, as far as anyone knows, has never been colonized by snakes. Today, the closest snakes are adders (Vipera berus) in both Scotland (470 mi away) and Norway (600 mi away), both of which are separated by a great deal of very cold ocean.


Unlike Iceland, Ireland was once connected to other land masses. Parts of it are at least 1.7 billion years old. At the end of the Precambrian, two pieces of rock that would become Ireland could be found beneath the sea, one piece connected to the continent of Laurentia and the other piece to the smaller continent of Avalonia, both around 80° South. Over the next 50 million years, these two parts drifted northward, eventually uniting and breaking sea level near the equator about 440 million years ago, in the Silurian Period. Throughout the late Paleozoic Era, Ireland sank back under the sea and gained 65% of its modern mass as limestone deposits from huge coral reefs. At the beginning of the Mesozoic, Ireland was at the latitude of present-day Egypt and had a desert climate, and by the time snakes evolved (150 million years ago, in the late Jurassic-early Cretaceous) Ireland had separated from any other land mass, and has been connected on and off to this day. There is some debate over how recently a land bridge connected Ireland with Great Britain and, by extension, mainland Europe, with the consensus resting on the idea that Ireland was isolated by ocean by 16,000 years ago, at which time the climate was still quite cold and there was a lot more ice in Ireland than there is now. Although it's not insane to think that snakes might have colonized Ireland from Europe sometime during the 90 million years that preceded the Pleistocene Ice Ages, as they have since re-colonized Great Britain, so far no one has found any snake fossils in Ireland. But, viviparous lizards, natterjack toads, and common frogs have managed to make it to Ireland, and the slowworm has been introduced there, so it could happen one day. Likely successful colonists include adders (Vipera berus), grass snakes (Natrix natrix), or smooth snakes (Coronella austriaca) from Great Britain, France, or Scandinavia. The Irish climate is highly moderated by the gulf stream, with much milder winters than expected for such a northerly area, so snakes could do quite well there.

Cape Verde

Cape Verde is an island country consisting of 10 volcanic islands in the central Atlantic Ocean, 350 miles off the coast of the western African countries of Mauritania and Senegal. The Cape Verde Islands were all formed by the same volcanic hot spot, the oldest 26 million years ago and the youngest just 100,000 years ago. They have never been colonized by snakes from mainland Africa. There is a single reference to the Striped Sand Snake (Psammophis sibilans) on the island of Sal in a 1951 paper that, according to the authors, was an accidental introduction from Guinea-Bissau. Neither this snake nor any other has ever been recorded again from Cape Verde, although the archipelago is home to 31 endemic lizard species, more than any other island chain in the Macaronesian region.

New Zealand

New Zealand was part of Gondwana (aka Gondwanaland), the more southerly of the two supercontinents formed by the breakup of Pangaea 200-180 million years ago. Gondwana comprised the present-day continents of South America, Africa, Australia, India, and Antarctica as well as New Zealand. Today, New Zealand is the highest part of a mostly-submerged continent called Zealandia that broke away from Gondwana between 100 and 80 million years ago. Since that time, New Zealand has developed a unique flora and fauna that does not include any terrestrial snakes, which makes sense since it has been isolated since around the dawn of their evolution (and has been mostly submerged several times since). However, a steady trickle of reports of sea snakes, borne by oceanic currents beyond their normal range to New Zealand waters and beaches, was summarized in 1997, at which time an amazing 69 records of 2 species were known, dating back to 1837 (more records and a third species have been added since). About 90% are of pelagic sea snakes (Hydrophis platurus; formerly Pelamis platurus, also known as yellow-bellied sea snakes), a very widespread species that is infamous for vagrancy and recently made headlines when one washed ashore in Ventura County, California. The remaining 10% of records are of banded sea snakes (Laticauda colubrina), a species that normally sticks more closely to shores, and judging by their morphology most of these have likely come to New Zealand from Fiji or Tonga. In 1995, one specimen in the British Museum collected in New Zealand in 1925 and formerly classified as L. colubrina was re-identified as a new species from New Caledonia, L. saintgironsi, by herpetologists revising the widespread Laticauda colubrina complex.

Map of pelagic sea snake records from New Zealand
From Gill 1997
High sea surface temperatures in 1969-1975 and again in 1988-1990 coincided with major influxes of tropical and subtropical fishes, sea turtles, and sea snakes (up to 16 a year) carried to New Zealand waters by the East Australian Current. Most records are of single animals, but in March 1985 four H. platurus were found on Tokerau Beach in Northland. About three-quarters of sea snake records are from Austral autumn (March-May), and many are from the north coast of the north island, but H. platurus has been found all around the North Island, including in the Cook Strait, and once even on the north coast of the South Island (at Pakawau, Golden Bay, in March 1974)! All L. colubrina records are from the north-east coast of the North Island, except for one at Castlepoint, Wairarapa, in August 1977. All records are of adult snakes, and most (79%) were alive when found, usually washed ashore, but occasionally swimming freely. One even swam up a stream near the sea! Even more amazingly, several sea snakes have been found alive inland from the coast, including a May 1938 record of H. platurus "some distance" from the sea at Table Cape on the Mahia Peninsula, a January 1990 record of L. colubrina "well above" the high-tide line at Whangaruru Harbour, an April 1938 record of H. platurus 200 feet from the sea on a lawn at New Plymouth, and, most incredible, a September 1945 record of L. colubrina alive at Te Aroha, near Hamilton, which is over 12 miles from an estuary over a range of hills or over 27 miles from the ocean along the Waihou River. Unlike H. platurus, which is almost incapable of moving on land, L. colubrina is reasonably good at terrestrial locomotion, which could explain the inland presence of these snakes. Alternatively, the author of the review paper suggested that the snakes could have been carried inland by birds.2

New Zealand also owns the Chatham Islands 560 miles to the east, the Kermadec Islands 620 miles to the north, and Tokelau 2000 miles to the northeast3, but no sea snakes have been reported from these islands, probably because so few people live there. Like vagrant birds, even the records from mainland New Zealand surely represent just a small percentage of the total number of marine reptiles that have reached New Zealand over the years. However, New Zealand is still widely considered to have no native snakes, since H. platurus  stop feeding at sea temperatures below 18°C and die at temperatures between 14.5 and 17°C (the average sea temperature in the coldest month in northern New Zealand is 16°C).


Kiribati is a Pacific Island nation that straddles the region of the central Pacific Ocean where the Equator and the International Date Line cross, making it the only country that is in all four hemispheres. It consists of four island groups totaling 32 atolls and one coral island. Of these, approximately the eastern half (the Phoenix and Line Islands) are apparently devoid of snakes; at least, they are listed as having no snakes in the most up-to-date and authoritative guide to the reptiles of the Pacific Islands. This guide takes a conservative approach in listing only species that are confirmed by a museum specimen or literature record, so it's possible that at least pelagic sea snakes are found in the waters of eastern Kiribati. What is certain is that the western half of Kiribati (Banaba and the Gilbert Islands) is home to breeding populations of banded sea snakes (Laticauda colubrina), and possibly pelagic sea snakes as well. Additionally, there is a single record of an ornate reef seasnake (Hydrophis ornatus), a species that is normally found much farther west, from the Gilbert Islands. This might represent a vagrant, but more likely it is a misidentified or mislabeled specimen. So, Kiribati has no terrestrial snakes, unless you count banded sea snakes, which mate, lay eggs, and sometimes digest food on land, but hunt, catch prey, and spend much of their time in the ocean.


Tuvalu is a Pacific Island nation south of Kiribati comprising three reef islands and six atolls and totaling 10 square miles, making it the fourth smallest country in the world. Like Kiribati, Tuvalu has no terrestrial snakes unless you count L. colubrina, but unlike Kiribati it has literature records of pelagic sea snakes off its shores. Happily, Tuvalu has decided to honor this species by putting it on one of its coins! It's a commemorative coin rather than a coin that's actually part of normal circulation, but still, it's pretty cool to have a snake on your money. Tuvalu is also home to at least 9 species of lizards and the introduced cane toad, so it's possible that snakes could show up there one day. In fact, it's even possible that a native, endemic blindsnake could have escaped detection on Tuvalu (or any other Pacific island) to this day. The only reason the Federated States of Micronesia aren't on this list is because of two unexpected species of endemic blindsnakes, Ramphotyphlops adocetus and R. hatmaliyeb, described in 2012 from two small islands, one in the eastern part of FSM and the other in the western part.


Nauru is a relatively isolated Pacific Island nation and is one of the only countries smaller than Tuvalu (at 8.1 square miles, only Monaco and Vatican City, both in Europe, are smaller). Unlike many Pacific Island nations, Nauru is a single island. Nauru has no native terrestrial snakes, but it does have H. platurus off its shores, and it also has what is likely an introduced species, the ubiquitous Indotyphlops braminus or Brahminy Blindsnake, the only unisexual species of snake. It's actually amazing to me that we're on the seventh entry and haven't encountered this species yet, considering how widespread it is globally. The original native range of I. braminus is unknown, but it probably evolved in continental Asia. Because a single individual constitutes a reproductively-competent population, it has since spread all over the world, and it's unclear how long it has been established on Nauru or elsewhere in the Pacific. Many similarly-widespread species in the Pacific owe their distribution to human-assisted transport, the precise timeline of which is difficult to determine. Given the harm done to Nauru's environment by phosphate mining during the 20th century, it's unlikely that any native terrestrial snake would have survived.

Marshall Islands

The Marshall Islands (see above map) have close political ties with the USA, but they are self-governing. They are located north of Kiribati, west of the FSM, and south of Wake Island. The authoritative guide to the reptiles of the Pacific Islands lists only I. braminus from the Marshall Islands, but other sources suggest that at least a few brown treesnakes (Boiga irregularis), infamously introduced to Guam, have been found there as well, and it's possible that H. platurus and possibly other sea snakes are found off its shores. Both the Gilbert Islands in Kiribati to the south and Pohnpei and Kosrae in FSM to the west have L. colubrina, although an official page states that the Marshall Islands have no sea snakes. So, as far as we know the Marshall Islands have no snakes that are native and terrestrial (unless you count I. braminus as native, considering that we don't know how long it's been there).

Vatican City

The Vatican is a walled enclave within the city of Rome, Italy, with an area of 110 acres and a population of 842, making it the smallest internationally-recognized independent state in the world, both by area and population. I couldn't find any references confirming or denying the presence of wild snakes in the Vatican, but other wildlife seem to be pretty minimal, which makes sense considering that Rome has been a large city for thousands of years. But, snakes and other wildlife can hang on in some amazingly urbanized places, so I wouldn't completely rule out the presence of a few of the eight species of snakes that can surely be found in the surrounding Italian countryside. Monaco, another European microstate with a very dense population and a high degree of urbanization, is another possibility for a snake-less nation, although, given Monaco's reputation as a playground for the rich and famous (30% percent of its population are millionaires), there are certainly some who meet an alternate definition of the word "snake" within its walls.

So there you have it: a maximum of ten countries out of 196 "without snakes", depending on where you want to draw the line. If we start expanding into territories or disjunct sections of larger countries, the list grows considerably, including places like Greenland, the Falkland Islands, Bermuda, Hawaii4, Wake Island, Johnston Atoll, Howland & Baker Islands, the Marquesas Islands, the Pitcairn Islands, Sala y Gomez, Isla Malpelo, St. Helena, the Faroe Islands, the Isle of Man, many Arctic and Antarctic islands, and Antarctica itself, which is owned by no country. And of course, as you can see from the map at the top, there are also large mainland areas of northern Europe, Asia, and North America, as well as the southern tip of Patagonia, that are too cold for snakes (although Vipera berus gets above the Arctic Circle in Scandinavia), not to mention the Atlantic, Arctic, and Antarctic Oceans5.

In the course of the research I did for this post, I found many travel articles promoting the snakelessness of some of these places as overwhelmingly positive, as I'm sure it is for many ophidiophobic travelers. But, the risk that snakes pose is way, way smaller than the fear we have of them, and in my mind the real danger is that many people see eradication of snakes as a positive thing, despite the fact that many of them are in real danger of extinction. Mauritius barely made it off this list, with one of two native species extinct and the other hanging on thanks only to captive breeding and reintroduction efforts. St. Kitts & Nevis could lose its only native snake, the Saba or orange-bellied Racer (Alsophis rufiventris), and native snakes have gone extinct or become critically endangered on many other islands throughout the Pacific and Caribbean due to centuries of forest clearance, overgrazing, development, and the introduction of invasive species, not to mention the many continental snake species threatened by sprawling development and habitat fragmentation. So, please, let's keep this list from growing.

1 Given the growing popularity of herpetoculture, I'd be willing to bet that there are captive snakes in every country, although a few countries have stringent laws banning any captive snakes, including as pets as well as in zoos and research facilities.

2 Studies have shown that, although many Pacific birds avoid pelagic sea snakes, naive Atlantic birds will try eat them (only to throw them up, since they are apparently poisonous as well as venomous). New Zealand's birds might be sufficiently naive to try to eat one.

3 Zug's Reptiles and Amphibians of the Pacific Islands lists Tokelau as having no snakes, not even sea snakes, but does not cover the Chatham or Kermadec Islands.

4 Hawaii has introduced Brahminy Blindsnakes and, unlike many Pacific Islands, it is known that these colonized the island chain more recently, in 1930, when they were imported from the Philippines in potted palm trees. Hawaii also has pelagic sea snakes and there are a few records of introduced brown treesnakes and boa constrictors, but neither species has established a breeding population (yet).

5 A study evaluating the probability that pelagic sea snakes could enter the Caribbean and Atlantic through the Panama canal, as lionfish have, concluded that there were no real barriers to their colonization of the eastern side of the Americas, but so far this has not happened.


Thanks to Kerry Nelson for doing some of the background research for this post as part of a discussion in the Wild Snakes: Education & Discussion Facebook group.


Edwards, R. J., and A. J. Brooks. 2008. The Island of Ireland: Drowning the Myth of an Irish Land-bridge? Pages 19-34 in J. J. Davenport, D. P. Sleeman, and P. C. Woodman, editors. Mind the Gap: Postglacial Colonisation of Ireland. Special Supplement to The Irish Naturalists’ Journal <link>

Gill, B. J. 1997. Records of turtles and sea snakes in New Zealand, 1837-1996. New Zealand Journal of Marine and Freshwater Research 31:477-486 <link>

Heatwole, H., S. Busack, and H. Cogger. 2005. Geographic variation in sea kraits of the Laticauda colubrina complex (Serpentes: Elapidae: Hydrophiinae: Laticaudini). Herpetological Monographs 19:1-136 <link>

Hecht, M. K., C. Kropach, and B. M. Hecht. 1974. Distribution of the yellow-bellied sea snake, Pelamis platurus, and its significance in relation to the fossil record. Herpetologica 30:387-396 <link>

McKeown, S. 1996. A Field Guide to Reptiles and Amphibians in the Hawaiian Islands. Diamond Head Publishing.

Vasconcelos, R., J. C. Brito, S. Carranza, and D. J. Harris. 2013. Review of the distribution and conservation status of the terrestrial reptiles of the Cape Verde Islands. Oryx 47:77-87 <link>

Wynn, A. H., R. P. Reynolds, D. W. Buden, M. Falanruw, and B. Lynch. 2012. The unexpected discovery of blind snakes (Serpentes: Typhlopidae) in Micronesia: two new species of Ramphotyphlops from the Caroline Islands. Zootaxa 3172:39–54 <link>

Zug, G. R. 2013. Reptiles and Amphibians of the Pacific Islands: A Comprehensive Guide. University of California Press, Berkeley, California, USA <link>

Creative Commons License

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

Tuesday, September 29, 2015

Can snakes hear?

Last month I wrote about whether snakes sleep, a topic that is far more interesting than the minuscule amount of research devoted to it. Another common question is whether snakes can hear, since they don't have external ear openings. The short answer is yes, snakes can hear, but the long answer is (as usual) more complicated. Happily, there is a good deal of research on this question, including a recent review. In general, many popular sources and some scientific ones have incorrectly claimed snakes to be deaf, whereas a plethora of behavioral, neurological, and physiological experiments, particularly those performed by the eminent Princeton hearing researcher Ernest Glen Wever in the 1960s and 70s, by UC-San Diego neurologist Peter Hartline in the 1970s, and by herpetologist and anatomist Bruce Young from the 1990s to the present, have conclusively shown that snakes can detect and respond to sounds.

Anatomy of the human ear
Most tetrapods have a three-part ear (outer, middle, and inner) that is useful for detecting airborne sounds. The boundary between the outer and middle ear is called the tympanic membrane or "ear drum", and its function is to convert airborne sounds from the outer ear into fluid-borne ones in the inner ear1, by way of one or more middle ear bones. Sounds are ultimately converted by auditory hair cells called stereocilia into nerve impulses, which travel to and are interpreted by the brain. At many stages along the way, the sounds are amplified by the vibrations they produce in the different parts of the ear, including the middle ear bones (more on these in a minute). It's been suggested that this three-part system evolved (possibly multiple times) around the beginning of the Triassic Period, in concert with the evolution of sound production in insects, the probable prey of many early amniotes. Many modern animals, such as songbirds, bats, dolphins, humans, frogs, and crocodilians, have very sensitive hearing that can detect extremely quiet airborne signals in spite of the presence of other competing noises.

Micro-CT scan of a ball python's skull and ear.
Red: mandible; dark blue: quadrate;
green: columella; purple/light blue: inner ear chambers

From Christensen et al. 2012
Click here for an interactive 3-D model.
You're probably familiar with the three bones of the middle ear in mammals, the malleus, incus, and stapes (also known as the hammer, anvil, and stirrup). Snakes and other reptiles have only a single middle ear bone, which is usually called the columella, although it is homologous with the mammalian stapes. The malleus and the incus evolved from the articular and quadrate bones in the lower jaw of early mammal-like reptiles, leaving modern mammals with a single lower jaw bone, the dentary. Modern reptiles still have three bones in their lower jaws, where they play a role in detecting vibrations, particularly those propagating through the ground. Most modern lizard ears are essentially like those of modern mammals, with a small external ear leading to a large ear drum close to the body's surface, which passes sound from the air (or the jawbones) to the columella and thence to the inner ear. In contrast, snakes lack all traces of an outer ear as well as an ear drum. Instead, a snake's columella is in direct contact with, and picks up vibrations from, its quadrate bone (the dark blue bone in the diagram above). You might suspect that this arrangement would only be useful for detecting ground-borne vibrations, and you'd be partially right: snakes are exquisitely sensitive to ground-borne vibrations. But, they can also detect airborne sounds.2

Diagram of the ear of a watersnake (Nerodia)
Modified from Wever 1978
Both older and several more recent experiments suggest that snakes can hear the vibrations produced by airborne sounds. Physiological data suggest that they are able to detect certain airborne frequencies directly using the inner ear, although the specific bioacoustic mechanisms remain poorly known. Instead, most airborne sounds are probably detected in using "somatic hearing". This happens when airborne sound waves strike a snake's body  and some of their energy is transferred to its bones, tissues, and organs, particularly the head and lung. The snake's vibration-sensitive hearing system can then pick up on and translate the vibrations from the rest of its body into fluid-borne vibrations and, ultimately, nerve impulses. So a snake probably can't hear, say, most music3 or human speech directly, but it can hear the sound of its own body vibrating in response to those sounds. So, instead of being deaf, snakes essentially have two auditory systems that are at least peripherally distinct. Whether signals from these two systems are integrated into a single neural pathway, as is the case for the eye and the pit organ, or whether they serve different functions, remains to be studied and determined.

The length and arrangement of the auditory hairs in the inner ears of snakes appears to be fairly uniform across species, at least relative to the variation seen in lizards, which can have very different auditory hair anatomy among families and often even among closely-related species. Snakes mostly have simple, tuatara-like papillae, which suggests that they have secondarily lost a more complex type of auditory organ. This might be due to the aquatic or burrowing lifestyle of their ancestors and/or to specializations of their lower jaws in response to their unusual eating habits. There is some variation in inner ear anatomy (and presumably in hearing capacity) among snakes: burrowing snakes have the longest papillae, arboreal snakes the shortest, and terrestrial snakes have papillae of intermediate length. Many mammals have over 10,000 auditory hair cells, whereas most snakes have only about 250 (although acrochordids have nearly 1,500). Supporting cells of unclear function are relatively more numerous in snakes and these cells have ultrastructural features that suggest that they are more specialized than those of other reptiles.

Hearing range of various animals, not including snakes
The louder and lower frequency airborne sounds are, the more easily a snake can detect them. This isn't entirely unlike our own hearing—although we do hear high-pitched airborne sounds directly more easily than snakes do, we also rely on amplification provided by our ear drums, inner ear hairs, and other parts of our bodies. Studies have shown that snakes can hear sounds in the 80-600 Hz range optimally, with some species hearing sounds up to 1000 Hz (for comparison, the range of human hearing is from 20-20,000 Hz). This means that a snake could hear middle C on a piano, as well as about one octave above and two below, but neither the lowest key (which is 27.5 Hz) nor the highest (which is 4186 Hz). The average human voice is around 250 Hz, which means that snakes can hear us talking as well. Of course, there is likely a lot of variation among snake species, and the hearing of most species has not been examined, so these are generalizations.

Use the player above to hear how the airborne parts of Led Zeppelin's classic "Good Times, Bad Times" would sound to a snake. Parts of the song below 80 Hz (some bass & drums) or above 600 Hz (almost all guitar, vocals, and cymbals) have been muted. This doesn't include their sensitivity to the groundborne vibration parts of the song, which you could simulate by turning the bass on your speakers all the way up.

Audibility curves for living reptiles, including birds (left). The lower
the curve, the quieter a sound can be detected at a given frequency.
You can see that snakes cannot hear very quiet sounds, but
otherwise are not that much worse than other reptiles
(although their hearing sucks compared to, say, owls).
Note the different y-axes. From Dooling et al. 2000.
What do snakes do with their hearing? Unlike frogs, birds, and insects, snakes don't seem to use sound for communication with each other. Although many snakes hiss and some use tail rattling, growling, scale rubbing, or cloacal popping to send messages to their would-be predators, these sounds are mostly above 2,500 Hz, so the snakes themselves cannot hear them. Some species are capable of producing sounds whose frequency overlaps with their hearing range, such as the loud, robust hisses of pinesnakes and gophersnakes (Pituophis), the bizarre and intimidating growling sounds of king cobras (Ophiophagus), and the famous rattles of some large rattlesnakes (Crotalus). Some people have suggested that rattlesnakes find their hibernacula by following the rattling sounds of other rattlesnakes, but this idea has been disproven because the power output of rattling is insufficient to serve as a long-distance signal, and playback experiments have not yielded a behavioral response to rattling.

Snakes might eavesdrop on the alarm calls of other, more vocal animals, as some lizards do with bird alarm calls, but probably not since most of these calls are between 2,500 and 10,000 Hz, well above their optimal frequency range. Most likely, snakes use their hearing to monitor their environment for sounds produced by approaching predators or prey, many of which are ground-borne vibrations. Snakes can hear in stereo and can use their hearing to determine the directionality and thereby the sources of sounds. One genus of snakes that probably relies quite heavily on vibration to hunt are Saharan sand vipers (Cerastes). These snakes ambush lizards and rodents from a position partially or completely buried in sand. Experiments have shown that their reliance on chemosensing and thermal cues was minimal and that, although snakes with their eyes obscured had altered strike kinematics, they were still able to capture prey.

1 This is necessary because "hearing" evolved under water. Many fishes and fully aquatic amphibians (such as amphiumas) have a network of hair-like cells all over their body, which is called a lateral line system. The lateral line allows them to sense water-borne vibrations using their entire body like one big eardrum. When early amniotes emerged onto land, the inner ear was still adapted to detecting fluid-borne vibrations, and the eardrum and outer ear evolved to facilitate collection of airborne sounds and translation of them into fluid-borne ones. These adaptations were further refined as amniotes began to hold their bodies off the ground (lizards, mammals) or fly (birds), minimizing their ability to pick up ground-borne vibrations with their ears. Snakes probably have a better capacity to pick up ground-borne vibrations than most amniotes, since at least some part of their body is in contact with the ground (or a tree) most of the time. To date, no one has examined hearing in fully aquatic snakes.

2 Many burrowing and aquatic amniotes have lost their external ear opening, because their need to detect airborne sounds is minimal, they can rely mostly on ground-borne vibrations, and their middle/inner ear could be damaged during burrowing or swimming if it was exposed. 
Amphisbaeneans and other lizards lacking external ears hear mostly ground-borne vibrations, which makes sense considering that many of them are fossorial and spend most of their lives with most of their bodies in contact with the ground. Amphisbaeneans have lost more of their airborne sound detection capacity than most burrowing lizards, in that, like snakes, they have also lost their tympanum and have their columella connected directly to their lower jaw (some naked mole rats have a similar jaw-middle ear connection and rely heavily on vibrational communication). One leading hypothesis suggests that snakes evolved from burrowing ancestors, and another suggests that they evolved from aquatic ancestors, so perhaps snakes lost and then regained an ability to hear airborne sounds. Other limbless squamates, such as pygopod geckos, specialize in making high-frequency vocalizations and have sensitive hearing to match.

3 At least two studies have investigated whether cobras can hear the music played by snake charmers, and concluded that cobras are responding to tactile and visual stimuli, not auditory.


Christensen, C. B., J. Christensen-Dalsgaard, C. Brandt, and P. T. Madsen. 2012. Hearing with an atympanic ear: good vibration and poor sound-pressure detection in the royal python, Python regius. The Journal of Experimental Biology 215:331-342 <link>

Clack. J.A. 1997. The evolution of tetrapod ears and the fossil record. Brain, Behavior, and Evolution 50:198-212 <link>

Dooling, R.J., R.R. Fay, and A.N. Popper. 2000. Comparative Hearing in Birds and Reptiles. Springer, New York, NY, USA <link>

Dooling, R. J., Lohr, B., & Dent, M. L. 2000. Hearing in birds and reptiles. Pp. 308-359 in Comparative Hearing in Birds and Reptiles. Ed. by Robert J. Dooling, Richard R. Fay, and Arthur N. Popper. Springer New York <link>

Friedel, P., B. A. Young, and J. L. van Hemmen. 2008. Auditory localization of ground-borne vibrations in snakes. Physical Review Letters 100:48701 <link>

Fuong, H., Keeley, K. N., Bulut, Y., & Blumstein, D. T. 2014. Heterospecific alarm call eavesdropping in nonvocal, white-bellied copper-striped skinks, Emoia cyanura. Animal Behaviour, 95:129-135 <link>

Hartline, PH. 1971. Physiological basis for detection of sound and vibration in snakes. Journal of Experimental Biology 54:349-371 <link>

Ito, R., & Mori, A. 2010. Vigilance against predators induced by eavesdropping on heterospecific alarm calls in a non-vocal lizard Oplurus cuvieri cuvieri (Reptilia: Iguania). Proceedings of the Royal Society of London B: Biological Sciences, 277:1275-1280 <link>

Köppl, C., Manley, G. A., Popper, A. N., & Fay, R. R. 2014. Insights from Comparative Hearing Research. Springer New York <link>

Manley, G. A. 2012. Peripheral hearing mechanisms in reptiles and birds (Vol. 26). Springer Science & Business Media <link>

Manley, G. A., & Fay, R. R. (Eds.). 2013. Evolution of the Vertebrate Auditory System. Springer Science & Business Media <link>

Wever, E. G. 1978. The Reptile Ear: Its Structure and Function. Princeton: Princeton University Press <not available online>

Wever, EG and JA Vernon. 1960. The problem of hearing in snakes. Journal of Auditory Research 1:77-83 <not available online>

Young, B. A. 1997. A review of sound production and hearing in snakes, with a discussion of intraspecific acoustic communication in snakes. Journal of the Pennsylvania Academy of Science 71:39–46 <not available online>

Young, B. A. 2003. Snake bioacoustics: toward a richer understanding of the behavioral ecology of snakes. The Quarterly Review of Biology 78:303-325 <link>

Young, B. A., & Aguiar, A. 2002. Response of western diamondback rattlesnakes Crotalus atrox to airborne sounds. Journal of Experimental Biology 205:3087-3092 <link>

Young, B. A., & Morain, M. 2002. The use of ground-borne vibrations for prey localization in the Saharan sand vipers (Cerastes). Journal of Experimental Biology 205:661-665 <link>

Young, B. A., N. Mathevon, and Y. Tang. 2014. Reptile auditory neuroethology: What do reptiles do with their hearing? Pages 323-346 in C. Köppl, G. A. Manley, A. N. Popper, and R. R. Fay, editors. Insights from Comparative Hearing Research. Springer, New York <link>

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

Monday, August 31, 2015

Do snakes sleep?

Do snakes sleep? Do they dream? These may seem like obvious questions, especially since almost every species of mammal, bird, reptile, amphibian, fish, and invertebrate studied has been found to exhibit some kind of resting phase. But sleep is hard to study in snakes, at least in part because they seem never to close their eyes. Consequently, there is shockingly little research on sleep in snakes. A Google Scholar search for the terms "snake+sleep" returns papers about venomous snakebites to sleeping victims, sleepwalkers dreaming about snakes, and papers by Stanford geophysicist Norman H. Sleep on the geology of the Snake River in Idaho. But, despite the dearth of research, I promise this post won't be too much of a snooze...

Human EEG "brainwaves"
Sleep is a behavior that involves an immobile posture, decreased responsiveness to arousing stimuli such as noise and light, and rapid reversibility (the ability to quickly "wake up", as distinct from hibernation or a comatose state). The physiological criterion most frequently used to define sleep is the slowing down of "brain-waves" on an EEG. An EEG (electroencephalogram) measures electrical activity in your brain, which is caused by your brain cells talking to one another. Brain activity, which happens even during sleep, appears as wavy lines on an EEG recording, hence brain 'waves'. When mammals and birds are sleeping, they exhibit two alternating patterns of EEG activity: 1) slow-wave sleep (SWS, also called synchronized, quiet, or non-REM sleep), which is characterized by high amplitude (75-400 μV), low frequency (0.5-4 Hz) EEG waves, and 2) "paradoxical" sleep (PS, also called desynchronized, active, or REM sleep), which is characterized by low voltage (5-10 μV), high frequency (13-30 Hz) EEG waves that are physiologically more like those in awake animals (hence the name "paradoxical"). In humans and cats, paradoxical sleep is associated with rapid-eye movement (REM, measured by electro-oculography or EOG), complete muscle relaxation (measured by electromyography or EMG), muscle twitching, irregular breathing/heartbeat, and, in humans at least, with dreaming.

Lizards wearing EEG-recording equipment while awake and asleep
From Flanigan 1973
Although sleeping patterns are enormously variable across the animal kingdom, most mammals and birds tested exhibit both SWS and PS, or variations on that theme. In some basal mammals and birds (echidnas, platypus, ostriches), eye movement and relaxed muscle tone are associated with both quiet and active sleep. Periods of rest or quiescence associated with EEG changes similar to those seen in mammalian sleep are clearly present in turtles and in crocodilians, but EEG data suggest that these animals do not exhibit REM sleep. Some experiments have found REM-like sleep in lizards, whereas others have not. Experiments in which lizards, turtles, and crocs were subjected to continuous arousal for 24-48 hours showed that they spent more time sleeping afterwards and that their brains produced more high-voltage spikes. Tortoises given the drug atropine, derived from the mandrake plant and used to produce deep sleep in humans since at least the fourth century B.C.E., also produced more spikes, suggesting that EEG spikes are in fact analogous signs of quite sleep in reptiles and mammals. Interpreting EEG data is complicated because SWS waves differ between mammals and reptiles, perhaps because reptile and mammal brains differ in structure, particularly with respect to the neocortex, the source of these waves in mammals. Furthermore, some reptiles sometimes seem to exhibit sleep-like brain activity when they are awake, perhaps because ectotherms basically fall asleep when they get cold.

Waking (top) and sleeping (bottom) python EEG
and EMG waves. From Peyrethon & Dusan-Peyrethon 1969
The single study of a snake was done by French comparative sleep researchers J. Peyrethon and D. Dusan-Peyrethon, who also studied sleep in fish, caimans, cats, and mice in the 1960s at the Laboratoire de Médecine Expérimentale in Lyon. They used EEG to monitor the brainwaves of a four-foot African Rock Python (Python sebae) over two days. They reported that sleep-like brain waves were produced almost 16 hours a day, increasing to over 20 hours following feeding, and that these brainwaves corresponded with slower breathing and heart rate, some muscle relaxation, and perhaps a lowered behavioral response threshold. They did not see any evidence for active sleep in the EEG. As far as I can tell, this is the only study ever conducted on sleep in a snake.

Snakes do have circadian rhythms, and many snakes are active only at particular times of day. Racers (Coluber), hog-nosed snakes (Heterodon), patch-nosed snakes (Salvadora), and sipos (Chironius) are strictly diurnal, whereas aptly-named nightsnakes (Hypsiglena), broad-headed snakes (Hoplocephalus), and kraits (Bungarus) are strictly nocturnal. But many snakes do not fit nicely into these categories. Good examples include ratsnakes (Pantherophis) and many vipers, but many other snakes may be active at any time of the day or night, depending on the time of year, so it's hard to predict when or for how long they might be expected to sleep. You often observe snakes exhibiting sleep-like behavior, sitting in one spot for hours, days, or even weeks at a time, like the Puff Adder (Bitis arietans) in the video at left. But the thing is, that snake is actually foraging. A viper might sit motionless for many days, such a long time that if a mammal exhibited that same behavior, we might think it was sick or dead! But in fact this is how many snakes forage for prey, hyper-alert to their immediate surroundings, ready to ambush, strike, and envenomate small animals that stray too close. Do they sleep when they are waiting, or are they awake the entire time? Radio-telemetry studies of bushmasters (Lachesis muta) in the wild suggest that they might have strict cycles of attentiveness, "awesomely alert during darkness and almost as if drugged by day", with relatively abrupt transitions each way. On the other hand, many marine mammals and migratory birds do not seem to sleep for long periods of time without suffering any obvious consequences. When engaged in constant activity, these animals close one eye and sleep one half of their brain at a time. Other animals, including perhaps some lizards, sleep one hemisphere at a time in contexts of high predation risk. Might snakes that use sit-and-wait foraging strategies do something similar?

I photographed this Sonoran Lyresnake (Trimorphodon lambda)
during the day, but it was found at night. Their skinny slit-like
pupils enhance their night vision, making distant
objects sharper by increasing the depth of field,
like using a small aperture on a camera lens.
If lyresnakes sleep, it's probably during the day.
How would a researcher tell if a snake was sleeping? Snakes never close their eyes. Or, more accurately, their eyelids are always closed, but they are covered by clear scales. Either in the wild or in captivity, observations of snakes seeming to "wake up" (implying that they were sleeping) are rare: motionless snakes rarely twitch, and other signs of PS are either normal for snakes (such as irregular breathing/heartbeat) or anatomically impossible (REM). You could imagine a series of experiments where an experimenter used EEG and high-speed infrared videography to record the brainwaves and behavioral responses of snakes to arousing stimuli. What stimuli to use is an open question, since snakes don't necessarily respond to bright lights or loud noises even when they're awake. Because snakes inhabit a primarily chemosensory world, it might be possible to wake one up using a smell. The human experience would suggest that the onset of chemosensory signals is inherently too gradual to really be surprising, but this might or might not be true for snakes. What about the infrared sense of some snakes? Could a bright infrared light wake them up? Can snakes see when they're asleep? What would that even be like? Only further studies will tell for sure.

So here's what we know: snakes probably do sleep, perhaps most of the time, but we don't really know when, for how long, how deeply, or whether or not they have paradoxical sleep, including dreaming. Sleep patterns are probably quite diverse across the >3500 species, of which only one has been examined. Many snakes do yawn, but this has been interpreted either as a means to gather chemical cues or to reposition musculoskeletal elements, in contrast with the hypothesized functions of yawning in humans (possibly regulating brain temperature, causing increases in blood pressure, blood oxygen, and/or heart rate in order to improve motor function and alertness, or as a social cue). Sleep is such a basic element of human biology, so if you ask me, the subject of sleep in snakes, and broader questions about the diversity, evolution, and function of sleep across the animal kingdom, should be keeping researchers awake at night.


Thanks to Kendal Morris for suggesting this question, and to Harry Greene, David Cundall, and Gordon Burghardt for sharing their observations.


Ayala-Guerrero, F., & Huitrón-Reséndiz, S. 1991. Sleep patterns in the lizard Ctenosaura pectinata. Physiology & Behavior 49:1305-1307 <link>

Bauchot, R. 1984. The phylogeny of sleep in vertebrates [birds, reptiles, amphibians, fish]. Annee Biologique (France) 23:367-392 <link>

Brischoux, F., Pizzatto, L., & Shine, R. 2010. Insights into the adaptive significance of vertical pupil shape in snakes. Journal of Evolutionary Biology 23:1878-1885 <link>

Campbell, S. S., & Tobler, I. 1984. Animal sleep: a review of sleep duration across phylogeny. Neuroscience & Biobehavioral Reviews 8:269-300 <link>

De Vera, L., González, J., & Rial, R. V. 1994. Reptilian waking EEG: slow waves, spindles and evoked potentials. Electroencephalography and Clinical Neurophysiology 90:298-303 <link>

Flanigan, W. F. 1973. Sleep and wakefulness in iguanid lizards, Ctenosaura pectinata and Iguana iguana. Brain, Behavior, and Evolution 8:417-436 <link>
Greene, H. W., & Santana, M. 1983. Field studies of hunting behavior by bushmasters. Estudios de campo del comportamiento de caza por parte de las cascabelas mudas. American Zoologist 23:897 <link>.

Hartse, K.M. and A. Rechtschaffen. 1974. Effect of atropine sulfate on the sleep-related EEG spike activity of the tortoise, Geochelone carbonaria. Brain, Behavior, and Evolution 9:81-94 <link>

Libourel, P. A., & Herrel, A. 2015. Sleep in amphibians and reptiles: a review and a preliminary analysis of evolutionary patterns. Biological Reviews <link>

Peyrethon, J., & Dusan-Peyrethon, D. 1969. Etude polygraphique du cycle veille-sommeil chez trois genres de reptiles. CR Soc Biol (Paris) 163:181-186 <not available online>

Rattenborg, N. C. 2006. Do birds sleep in flight? Naturwissenschaften 93: 413-425 <link>

Roe, J. H., Hopkins, W. A., Snodgrass, J. W., & Congdon, J. D. 2004. The influence of circadian rhythms on pre-and post-prandial metabolism in the snake Lamprophis fuliginosus. Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology 139:159-168 <link>

Siegel, J. M. 2008. Do all animals sleep? Trends in Neurosciences 31: 208-213 <link>

Siegel, J. M., Manger, P. R., Nienhuis, R., Fahringer, H. M., Shalita, T., & Pettigrew, J. D. 1999. Sleep in the platypus. Neuroscience 91: 391-400 <link>

Tauber, E.S., J. Rojas-Ramirez, and R. Hernandez-Peon. 1968. Electrophysiological and behavioral correlates of wakefulness and sleep in the lizard (Ctenosaura pectinata). Electroencephalography and Clinical Neurophysiology 24:424–443 <link>

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

Tuesday, July 7, 2015

Snakes that decapitate their food

Crab-eating Snake (Fordonia leucobalia) eating a crab
A few years ago I wrote an article about southeast Asian crab-eating snakes, the only snakes (at the time) known to break apart their food instead of swallowing it whole. Although I ended that article by wondering how many more strange snake dietary adaptations we might discover, I didn't actually anticipate writing a sequel to that article—it was so unique that the BBC filmed it for their series Life in Cold Blood, and I doubted that anyone would discover another snake that tore apart its prey. You can imagine my surprise when recently I was asked to review a paper about another snake that breaks its food apart! I was also delighted that this snake was a scolecophidian, because I feel that they are underrepresented both on this blog and in snake biology in general. It is a bit unsatisfying that it is the Brahminy Blindsnake (Indotyphlops braminus, formerly known as Ramphotyphlops braminus), the best studied scolecophidian by far by virtue of its enormous range and unusual breeding habits, but I think this exciting discovery could become extended to some or most of the other >400 species of blindsnakes.

A blindsnake with decapitated termite heads
stuck to the back of its head
Late last year, herpetologist Yosuke Kojima, a postdoctoral researcher at Kyoto University, and entomologist Takafumi Mizuno, a graduate student at Kyoto Institute of Technology, made a chance finding. They had been close friends since elementary school and shared an interest in behavioral and chemical ecology. Together, they planned some experiments to learn more about interactions between blindsnakes and their primary prey, ants. Mizuno's lab also kept colonies of termites (in this case, Reticulitermes speratus), which are also eaten by blindsnakes. Blindsnakes are unusual in that they eat many small prey at a time rather than a few large prey infrequently. Blindsnakes often eat 20 or more prey items at a time, and the maximum number of prey items ingested by a single individual is 1,431 for Anilios (Ramphotyphlops) nigrescens from Australia. Because blindsnakes often gorge themselves when feeding in an ant or termite nest, they often eat very quickly, using a raking technique of the mandibles (in leptotyphlopids) or of the maxillae (in typhlopids). Nate Kley's lab at Stony Brook University has taken some fantastic videos of blindsnake feeding techniques.

Time-sequence of a blindsnake ingesting and decapitating
a termite worker. From Mizuno & Kojima 2015
Supplementary video here
As Mizuno fed termites to the blindsnakes, he observed something very unusual. The blindsnakes typically grabbed and swallowed the termites backwards. Most snakes usually swallow their prey head-first, so this was weird enough. But, it gets weirder. Often, when the snake had maneuvered a termite so that only its head stuck out of the snake's mouth, it would rub its face on the bottom of the tank, decapitating the termite. All of the termite soldiers and about half of the termite workers offered to the blindsnakes were decapitated. Occasionally, a snake would regurgitate a termite that it had consumed whole, decapitate it, and re-consume the body. Decapitated termite heads became attached to the back of the snake’s head or were scattered around the bottom of the cage. The snakes never ate the decapitated heads. There did not appear to be a cost to decapitation—whether a snake decapitated a termite or not, the time required to completely ingest it was about 3 seconds. However, twice blindsnakes were observed swallowing termites head-first, which took only about 1-1.5 seconds. This may not seem like a big difference, but when you're eating hundreds or thousands of prey items in one sitting, it can add up!

Intact termite heads in the feces of a blindsnake
From Mizuno & Kojima 2015
Why do blindsnakes remove the heads of their prey? One reason might be that termite heads contain glands full of toxic chemicals called terpenes. But, unlike predators that remove the skin of various amphibians to avoid the toxins in their skin glands, blindsnakes don't always remove the heads of their prey, suggesting that they aren't that susceptible to terpene poisoning. It's even been suggested that some blindsnakes might be sequestering defensive chemicals from the ants and termites that they eat, just as gartersnakes sequester tetrodotoxin from newts, in which case they might actually prefer the part of the termite with more chemicals. A more likely hypothesis is that the heads are less digestible than the termites' bodies. Between 26 and 100% of the termite heads consumed by blindsnakes in Mizuno & Kojima's experiment remained undigested in the snakes' feces. Additionally, the snakes preferred to eat the worker termites rather than the more heavily-armored soldier termites, and the few soldier termites they did eat were newly-molted. Removing the termites' scleritized heads might allow blindsnakes to pack more soft, squishy bodies into their stomachs, maximizing the nutrition they get out of their meals. It's a bit like you or me peeling a banana or an orange, or removing the husk from a coconut. Since soldier termites have pinching mandibles, removing their heads might also prevent the blindsnakes from being bitten from the inside, which is a bit like you or me...removing the horns of a cow before eating it, if we ate cows alive and whole, I guess?

Evidently the raking maxillae of typhlopids
are sufficiently dexterous to manipulate
prey inside the mouth to position them
for decapitation.
From Kley 2001
Since snakes don't have hands, they've got to remove any indigestible parts using the only maneuverable part they do have—their jaws. Unlike other blindsnakes (which use bilaterally synchronous jaw movements similar to those of all other vertebrates) but like alethinophidians, typhlopid blindsnakes can move the left and right sides of their highly mobile upper jaws independently and asynchronously. Despite its sophistication, the ratcheting movements of their maxillary raking mechanism are insufficient, by themselves, to allow them to decapitate their prey. We must await further functional-morphological studies to assess the role of the toothless lower jaw, which could act as a wedge or blade, in this process. Since snakes cannot really "bite", arthropods, with their jointed limbs and bodies, might be the only type of prey that a snake could pull apart. There are a fair number of snakes that eat arthropods, but most of them are relatively obscure. Besides the crab-eating snakes, one might look for prey-dismembering behavior in sonorines, a tribe of desert-dwelling snakes from southwestern North America, other North American snakes such as the colubrines Tantilla and Opheodrys and the natricine Regina, the dwarf racers of Africa and the Middle East (genus Eirenis), the centipede-snakes of Africa (genus Aparallactus), or certain kukrisnakes (genus Oligodon). In addition to the typhlopid blindsnake in this study, two short notes from the 1950s and 60s document similar decapitation behaviors in two different species of leptotyphlopids (Epictia goudotii [formerly Leptotyphlops phenops] from Central America and Rena dulcis [formerly L. dulcis] from Texas), despite their radically different jaw morphology. I won't be surprised if it turns up in other scolecophidian families as well, since this most-basal group of living snakes probably co-evolved with the early radiation of ants and termites, their favorite prey.


Thanks to Brendan Schembri for the use of his photo, and to Takafumi Mizuno and Yosuke Kojima for giving me the opportunity to write about their discovery in advance of its publication and for translating it into Japanese.


Kley, N.J. 2001. Prey transport mechanisms in blindsnakes and the evolution of unilateral feeding systems in snakes. American Zoologist 41:1321-1337 <link>

Mizuno, T. and Y. Kojima. In press. A blindsnake that decapitates its termite prey. Journal of Zoology 10.1111/jzo.12268 <link>

Prestwich, G.D., B. Bierl, E. Devilbiss, and M. Chaudhury. 1977. Soldier frontal glands of the termite Macrotermes subhyalinus: Morphology, chemical composition, and use in defense. Journal of Chemical Ecology 3:579-590 <link>

Reid, J.R. and T.E. Lott. 1963. Feeding of Leptotyphlops dulcis dulcis (Baird and Girard). Herpetologica 19:141-142  <link>

Savitzky, A.H., A. Mori, D.A. Hutchinson, R.A. Saporito, G.M. Burghardt, H.B. Lillywhite, and J. Meinwald. 2012. Sequestered defensive toxins in tetrapod vertebrates: principles, patterns, and prospects for future studies. Chemoecology 22:141-158 <link>

Shine, R. and J.K. Webb. 1990. Natural history of Australian typhlopid snakes. Journal of Herpetology 24:357-363 <link>

Smith, H.M. 1957. Curious feeding habit of a blind snake, Leptotyphlops. Herpetologica 13:102 <link>

Stokes, A.N., A.M. Ray, M.W. Buktenica, B.G. Gall, E. Paulson, D. Paulson, S.S. French, E.D.B. III, and J. E.D. Brodie. 2015. Otter predation on Taricha granulosa and variation in tetrodotoxin levels with elevation. Northwestern Naturalist 96:13-21 <link>

Vidal, N., J. Marin, M. Morini, S. Donnellan, W.R. Branch, R. Thomas, M. Vences, A. Wynn, C. Cruaud, and S.B. Hedges. 2010. Blindsnake evolutionary tree reveals long history on Gondwana. Biology Letters 6:558-561 <link>

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