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Friday, October 30, 2015

Are there any countries without snakes?


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

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.

Ireland

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
(1837-1997)
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

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

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

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.

Cover of a joke book that's blank inside
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.


ACKNOWLEDGMENTS

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.

REFERENCES

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.




2 comments:

mike arthur said...

You mentioned the Chatham and Kermadec Island groups, both of which are governed by New Zealand and therefore part of NZ.. I guess if there were snake populations there New Zealand wouldn't be considered snake free?
An interesting point. Since the late 1800's unconfirmed reports have popped every now and then, of a small population of Australian copperheads on the rugged isolated west coast of the south islands. While none of these reports have been officaly confirmed , given the areas isolation and lack of human inhabitants and the copperheads secrecy it's not inconceivable that there is something to these report...

Andrew Durso said...

Thanks for your thoughtful comment Mike. There certainly is a lot more to the question "Are there snakes in New Zealand?" than I ever thought. I would argue that most people probably don't think of the Chatham and Kermadec Islands when they think of New Zealand; probably most people have never even heard of them, especially outside of NZ. I do think it's possible that snakes could be there, especially in the subtropical Kermadecs, most likely sea snakes but possibly others as well (look at those Micronesian blindsnakes!). On the other hand, if there were snakes there, saying that NZ has snakes for that reason would be like saying that there are Brown Treesnakes in the USA because they are on Guam—technically accurate, but somewhat misleading. It's certainly true that the vast majority of the North and South Islands have no snakes, most of the time (unconfirmed reports of Austrelaps notwithstanding). That's one of the things I like most about snakes—they are always surprising us!