Screech Owls and Blindsnakes: An Unlikely Mutualism

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Adult Eastern Screech Owl at a nest box

In the 1970s and 80s, a pair of biologists at Baylor University in Waco, Texas, Fred Gehlbach and Robert Baldridge, were studying screech owl nesting ecology. These small owls nest in tree cavities and eat a variety of small animals, from insects to mice. Like most raptorial birds, Eastern Screech Owls usually kill their prey before bringing it home to feed to their nestlings. Gehlbach and Baldridge observed some of the screech owls in their study carrying live Texas Blindsnakes (Rena [formerly Leptotyphlops] dulcis) to their nests in experimental nest boxes like those used by wood ducks and bluebirds (pictured at right). When they checked the nests the next day, they found, to their surprise, between one and fifteen live blindsnakes living among the owl chicks in fourteen different nests! In some cases, the snakes lived with the baby owls for at least a week! Many of the blindsnakes bore scars from adult owl beaks, but few had been killed.

If you're not familiar with blindsnakes (aka scolecophidians), don't worry; few people are. There are about 400 species of these 'seriously strange serpents', as Darren Naish calls them over at TetZoo, distributed chiefly in the world's tropical regions (the Texas Blindsnake is one of the few temperate exceptions). Most have small eyes (or none at all, as their name suggests), smooth round scales, and eat invertebrates. Their jaw architecture is entirely unique: their jaws act like little scoops to effectively shovel ant and termite larvae and pupae into their mouths. Check out the video from BBC's Life in Cold Blood below, or visit the homepage of blindsnake biologist Nate Kley at Stony Brook University.

Almost as cute as baby snakes

How does this help baby screech owls? Gehlbach and Baldridge wanted to find out, so they measured the diversity and abundance of invertebrates in the owl nests with and without live blindsnakes, as well as the health and survival of the baby owls (which they were already measuring). They found that nests with blindsnakes had significantly fewer mites, insects, and arachnids, and that baby owls from these nests were 25% more likely to survive and grew as much as 50% faster; in other words, the presence of the blindsnakes improved the health of the baby owls and the fitness of the adults. The effects were more pronounced for the youngest owl babies, which hatch as many as six days later than their oldest sibling. As the nail in the coffin, Gehlbach and Baldridge tested whether or not the blindsnakes actually ate the invertebrates they found in the owl nests, and sure enough, they chowed down on the soft-bodied fly larvae that kill baby owls in nearly 30% of nests.

Texas Blindsnake (Rena dulcis)

They also noticed that blindsnakes were more likely to be found in nests after it rained, probably because the mother owls had an easier time of finding the blindsnakes when they were crawling around on the surface, which many fossorial snakes tend to do when rainwater fills their burrows. Gehlbach and Baldridge also found that blindsnakes could only survive about two weeks in owl nest boxes that did not contain baby owls, suggesting that they were dependent on insect larvae that entered the nest inside food brought by the mother owl. These snakes can climb trees, so presumably it isn't too challenging for them to climb down out of a nest box after it is vacated by owls; one gravid female blindsnake was found in a nest box, so it is possible that they lay their eggs there before leaving. Some nests contained dead blindsnakes, which Gehlbach and Baldridge hypothesized had been eaten by the baby owls after their food supply had run out. In feeding experiments, baby screech owls readily consumed dead blindsnakes as well as other snakes of similar size, such as Rough Earthsnakes (Virginia striatula).

Skull architecture of Rena dulcis

The skulls of blindsnakes are just amazing, and it's thanks to the research efforts of blindsnake anatomist Nate Kley of Stony Brook University that we know so much about them. Kley has characterized the feeding behavior of two families of blindsnakes, the Leptotyphlopidae, which use  scooping motions of the lower jaw known as mandibular raking, and the Typhlopidae, which use similar motions of the upper jaws, called maxillary raking. It's remarkable how similar the two strategies are given that the snakes are using entirely different parts of their bodies to employ them and that they are separated by about 110 million years of evolution. High-resolution CT scans of the skill of Rena dulcis are also available from the good people at UT Austin's DigiMorph project. The jaws (upper in typhlopids, lower in leptotyphlopids) move about independently of the skull to a remarkable degree. You can get a really good idea of that motion by watching videos of leptotyphlopids here, here, and here, and of typhlopids here and here. As soon as they're in the mouth, those larvae are goners! These snakes are unlike all others in that they eat  huge numbers of prey items very quickly, thanks to their unique jaw architecture. One Blackish Blindsnake (Austrotyphlops nigrescens) from Australia was recorded to have eaten over 1,431 ant larvae/pupae in one sitting! Some blindsnakes have cloacal secretions that aid in repelling attacking ants or chemically camouflaging the blindsnakes, which live inside ant mounds. The list of amazing attributes goes on and on - and there is much more for scientists to find out!

ACKNOWLEDGMENTS

Thanks to Count_Strad, Toby Hibbits, Gary Nafis, and Nate Kley for use of their photos and figures.

REFERENCES

Gehlbach, F. and R. Baldridge. 1987. Live blind snakes (Leptotyphlops dulcis) in eastern screech owl (Otus asio) nests: a novel commensalism. Oecologia 71:560-563. <link>

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

Malagasy Leaf-nosed Snakes

Langaha madagascarensis male

Madagascar has been called the "eighth continent" as a result of its large size, unique habitats, and high faunal and floral (not to mention cultural and linguistic) endemism. Of the ninety-six species of snakes inhabiting the island, only two are found anywhere else: one is a sea snake (the widespread Pelamis platura) and the other is a ubiquitous introduced species (the parthenogenetic blindsnake Ramphotyphlops braminus). Most of the rest belong to the subfamily Pseudoxyrhophiinae, and each deserves its own article. But one has to start somewhere, and perhaps the best place to start is with one of the most unique Malagasy snakes, and one of my favorites: Langaha madagascarensis, the Malagasy Leaf-nosed Snake.

Langaha madagascarensis female

Langaha is so unique that it has been placed in its own genus ever since it was described, and was one of only eight¹ genera recognized in Bonnaterre's 1790 Ophiologie, a book that covered 224 species of snake. That's right: at a time when snakes as different as wormsnakes, saw-scaled vipers, sea snakes, and blunt-headed tree snakes were being grouped together as "typical snakes" in the genus Coluber, Langaha was considered unusual enough to justify its own genus! Today there are three recognized species of Langaha, but the most is known about L. madagascarensis.

Left: Captive juvenile Langaha madagascarensis exhibiting hanging behavior; photo from Krysko 2003
Right: Seed pods of the Ophiocolea floribunda, a Malagasy legume whose genus is Greek for 'hollow snake'

As their name implies, Leaf-nosed Snakes have bizarre nasal appendages. What's more, these structures are sexually dimorphic to a degree unusual among snakes. Female Leaf-nosed Snakes have a more elaborate, serrated nasal appendage, whereas males bear a longer, pointier one. These structures are present at birth, suggesting that they have some function beyond sexual signaling between rival males or potential mates. Often, these snakes are seen hanging from branches with their heads pointing towards the ground - perhaps the structures serve to drain water off the snake? Several Malagasy plants, including some legumes and bignonias, have long pointed seed pods that hang down from the plant, providing possible models that the snake may imitate with its posture and nasal appendage. No one knows for certain.

Male (right) and female
(left) L. madagascarensis 

This is a timely post in that it comes on the heels of newly published research on Malagasy Leaf-nosed Snakes. An article by recent Cornell University graduate Jessica Tingle has just appeared in the journal Herpetological Conservation and Biology documenting novel aspects of the behavioral ecology of this unusual snake. Everything known about the behavior of Langaha to date has been learned from observing captive individuals. Tingle's paper presents the first data collected on the behavior of Langaha in the wild. She observed several of these snakes foraging for and eating lizards, although one sentence in her paper stands out to me as typical of snake behavior studies: "The vast majority of their time (90%) was spent not moving at all." Although this sounds boring, it provides evidence that these snakes are primarily ambush predators, rather than active foragers (although Tingle did observe one Langaha chasing skinks on the ground). Spending months in Madagascar, Tingle was able to observe only a few snakes, and much remains to be learned about their natural history and ecology.

Plate showing a male Langaha madagascarensis from Bonnaterre's 1790 Ophiologie

From observations made on Langaha in captivity by Kenney Krysko of the Florida Museum of Natural Sciences, we know that Leaf-nosed Snakes lay eggs. When they hatch, the nasal appendages of juveniles are folded up so that their egg tooth can be used to break out of the egg. The appendage gains its normal shape after 36 hours. Juveniles exhibit the same vertical 'hanging' behavior as adults, which Krysko also suggests helps them mimic the seed pods of Malagasy plants (and perhaps deter predation, though by what predator is unclear).

Hatchling Langaha madagascarensis, from Krysko 2003

The other two species of Langaha are very poorly known. In Darren's TetZoo article, he states that only female Langaha alluaudi have nasal appendages, but I have been unable to find another source corroborating this fact, although I did find a photo on Flickr purported to be a male L. alluaudi (it looks similar to a male L. madagascarensis, also sometimes called L. nasuta, to me). Female L. alluaudi have longer, straighter nasal appendages than L. madagascarensis, and female L. pseudoalluaudi have shorter, more upturned ones (no word on what male L. pseudoalluaudi might look like). Why these differences? Perhaps differences in microhabitat or sexual preference are the cause. Who can say?

Female (left) and male(?, right) Langaha alluaudi

Female L. pseudoalluaudi

Although Madagascar is unique, it is similar to the rest of the world in at least one sad way: its natural places are disappearing quickly. Most of its forests have already been logged or converted to slash and burn agriculture, and what little remains is dwindling daily. If more effective conservation measures are not taken,  including supporting the human communities that depend on the rich natural resources of this hottest of biodiversity hotspots, we may never find out what Langaha's nose is for.

Male L. madagascarensis consuming Chalarodon madagascariensis
Photo from Herp. Con. Bio. gallery for Tingle 2012

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1 Three of these eight genera turned out not to be snakes at all: the limbless lizards Anguis and Amphisbaena, and  the limbless amphibian Caecilia.↩

ACKNOWLEDGMENTS

Thanks to Dick Bartlett, Jessica Tingle, David d'O, Bernard Dupont, Russell Speight, and G.E. Schatz for use of their photos.

REFERENCES

Bonnaterre PJ (1790) Ophiologie, in Tableau encyclopédique et méthodique des trois règnes de la nature. Panconoke, Paris <link>

Krysko KL (2003) Reproduction in the Madagascar leaf-nosed snake, Langaha madagascariensis (Serpentes: Colubridae: Pseudoxyrhophiinae). African Journal of Herpetology 52:61-68 <link>

Krysko KL (2005) Feeding behaviour of the Madagascar leaf-nosed snake, Langaha madagascariensis (Serpentes: Colubridae: Pseudoxyrhophiinae), with an alternative hypothesis for its bizarre head structure. African Journal of Herpetology 54:195-200 <link>

Tingle JL (2012) Field observations on the behavioral ecology of the Madagascan Leaf-nosed Snake, Langaha madagascariensis. Herpetological Conservation and Biology 7:442-448 <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.

Africa's Giant Gaboon Vipers

For as long as I can remember, I've been impressed by Gaboon Vipers (Bitis gabonica). These western African behemoths can reach 5 3/4 feet in length and over 14.5 inches in girth, and weigh up to 25 pounds with an empty stomach. They are the heaviest vipers and possess the longest fangs, up to one and a half inches in length! Furthermore, their geometric dorsal pattern, as intricate as it is beautiful, is ideally suited to camouflaging them against the leafy forest floor, where they lie in wait for their endothermic prey: birds, rodents, rabbits, monkeys, small antelope, porcupines.

A Gaboon Viper, beautifully camouflaged

Like many vipers, Gaboon Vipers are ambush predators, a lifestyle to which they are supremely adapted. Long folding fangs and deadly venom allow them to kill their prey while keeping a safe distance from it. A very low metabolism permits them to wait in one spot for weeks, until the perfect opportunity presents itself. They spend between three-quarters and 95% of their time just sitting quietly, sometimes for up to three months at a time. Every so often, a viper, particularly a male during the breeding season of March through May, will embark on a long-distance movement of one quarter to two thirds of a mile, sometimes in a single day.¹ The preferred habitat of Gaboon Vipers is a mosaic of forest, thicket, and grassland, although they will sometimes enter sugarcane fields and rural gardens. As with most snakes, life as a Gaboon Viper is probably pretty dull.

The impressive fangs of a Gaboon Viper

In spite of its impressive size, or perhaps because of it, Gaboon Vipers are, like many of their kin, docile and retiring. "On two occasions, I accidentally stepped directly on B. gabonica during the course of radiotracking, only becoming aware of this after feeling squirming movement beneath my foot. At no point during either encounter did the snake hiss or show aggression in any manner", writes Jonathan Warner in his dissertation, which also contains evidence that hippos, elephants, and leopards may walk right by Gaboon Vipers without noticing them. Being stepped on and squashed by these large herbivores might be the primary cause of mortality for adult vipers, which are not vulnerable to many natural predators.

You can see why

Although Gaboon Vipers produce prodigious amounts of venom (nearly 10 mL), the toxicity is rather low compared to other venomous snakes, and there are only a few detailed clinical reports of bites. They are undoubtedly dangerous snakes, but envenomations are few compared to such infamous species as the Russell's Viper. Like most snakes, particularly slow-moving ones with good camouflage, Gaboon Vipers usually sit still and remain unnoticed whenever a human comes nearby (so in other words, pretty much the exact same thing they were already doing).

Gaboon Viper plate from Duméril, Bibron, & Duméril's Erpétologie Générale;
unfortunately, this is one of the only plates not in color

Like most vipers, female Gaboon Vipers give birth to a litter of live young once every two to three years, usually between 20 and 40. Females do not eat while pregnant. Little is known about their reproductive behavior, but males combat one another over females, which must be an impressive sight. Much recent research on Gaboon Vipers has taken place in South Africa, where they are known as Gaboon Adders. In the southernmost populations, which are disjunct from the main range of the species, the climate is subtropical and seasonal differences in activity are observed, but radiotelemetry studies conducted in tropical areas of Cameroon and Nigeria show no seasonal changes in behavior.²

East African Gaboon Viper (B. g. gabonica)

What's the thing on their nose for? It is much larger in the West African subspecies than in the East African one. Hypotheses range from enhancing crypsis to doing nothing at all. Darren Naish at Tetrapod Zoology has addressed this question, but it seems he met with about the same amount of success as I did in finding a compelling, well-supported reason why these snakes have horns. I couldn't find any studies that examined whether the horns had a sensory function, although it certainly seems possible.

West African Gaboon Viper (B. g. rhinoceros)

I learned something new about these vipers recently. It seems that, among other heavy-bodied snakes, they have evolved the ability to retain their feces for incredibly long periods of time - months to years, after which time 5-20% of the body weight of a single snake may be feces. While this would kill a human, retained fecal material may be functioning as metabolically inert ballast in these species, which require a stationary inertial base for striking. Available data suggest that enhanced uptake of water and nutrients can also be achieved in snakes retaining feces - the poisonous urates (read: pee) are excreted more frequently. Amazing.

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1 One exception is that these snakes always move following shedding, which occurs about twice a year, perhaps to distance themselves from potential predators attracted by the sloughed material or to avoid external parasites in the old skin that could reattach to the snake.^↩

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2 Snake biologists in Africa face challenges unfamiliar to we North Americans: "In several instances, I had to abort tracking efforts due to B. gabonica locations in close proximity to potentially dangerous game; namely [Water Buffalo, Rhinoceros, Elephant, Hippopotamus, and Crocodile]", writes Jonathan Warner in his dissertation.^↩

ACKNOWLEDGMENTS

Thanks to Tim Vickers, Wolfgang Wuster, Ivica, Markus Oulehla, and Jonathan Warner for their photos.

REFERENCES

Lillywhite HB, de Delva P, Noonan BP (2002) Patterns of gut passage time and chronic retention of fecal mass in viperid snakes. In: Schuett GW, Höggren M, Douglas ME, Greene HW (eds) Biology of the Vipers. Eagle Mountain Publishers, Eagle Mountain, UT, pp 497-506

Linn I, Perrin M, Bodbijl T (2006) Movements and home range of the gaboon adder, Bitis gabonica gabonica, in Zululand, South Africa. Afr Zool 41:252-265

Luiselli L (2006) Site occupancy and density of sympatric Gaboon viper (Bitis gabonica) and nose-horned viper (Bitis nasicornis). J Trop Ecol 22:555-564

Marsh NA, Whaler BC (1984) The Gaboon Viper (Bitis gabonica): Its biology, venom components and toxinology. Toxicon 22:669-694

Warner JK (2009) Conservation Biology of the Gaboon Adder (Bitis gabonica) in South Africa. PhD dissertation, School of Animal, Plant, and Environmental Sciences, University of the Witwatersrand, Johannesburg, South Africa.

This Gaboon Viper quilt was made for me by
my mother on my 21st birthday.
The geometric pattern lends itself perfectly
to quilting.

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

Galápagos Racers

For answers to your questions about the Galápagos Racer/Marine Iguana chase scene from Planet Earth II, click here!

Sadly, snakes are inactive this time of year in northern Utah. With lower-than-average temperatures dipping below 0° F every night, I've had a lot of time indoors to read and daydream about snakier times and places. You can imagine my envy of my colleagues Susannah French, Nick Kiriazis, and Lori Neuman-Lee, who are currently in the Galápagos Islands studying Marine Iguanas. Nick, a student teacher at South Cache Middle School in Hyrum, Utah, is blogging about their research experiences at his blog, The Learning Scientist, which you should check out. Before they left, I instructed them that they were not to pass up an opportunity to observe the endemic racers of the Galápagos, the only snakes to inhabit the famous archipelago (other than one sea snake species, found offshore).

Galapagos Snake from Bartholome Island

Before I began the research for this article, I was under the impression that there was only a single species of Galápagos Racer. But speciation is quick to act in the birthplace of research on evolutionary principles, and in fact there are five species, each inhabiting different groups of islands. This isn't too surprising. As with most organisms inhabiting the Galápagos (and archipelagos in general), new species evolve on different islands over a relatively short period of time. Archipelagos are natural classrooms for evolutionary biologists, each island differing slightly in a number of qualities: size, rainfall, elevation, isolation. These differing characteristics, combined with long periods of reproductive isolation from populations on other islands, result in the evolution of endemic species to each island or group of closely spaced islands. Many groups of organisms have colonized the volcanic Galápagos from South America since the islands rose from beneath the sea some 8 million years ago. In that time, many of the plants and animals have diversified and speciated, leaving behind a pattern of relationships so telling that the idea of evolution by natural selection was formulated based on observations Charles Darwin made of the islands' fauna (for a recap, follow the link above to see a video to which my friend Rosemary Mosco contributed artwork).

Galapagos Snake eating a lava lizard (Microlophus sp.)

Although one might think that Darwin probably discovered most of the species native to the Galápagos Islands, others had been there before him. The first mention of these snakes in the scientific literature came 80 years before Darwin was born, by explorer William Dampier, a natural historian whose scientific accomplishments have been largely overshadowed by his reputation as a buccaneer. In his 1729 memoir, New Voyage Round the World, he wrote "There are some Green Snakes on [the Galápagos]; but no other land-animal that I did ever see." (Although they are hardly green.) In 1839 Darwin wrote "There is one snake which is numerous; it is identical, as I am informed by [French herpetologist Gabriel] Bibron, with the Psammophis Temminckii from Chile." This turned out not to be true, and the snakes were officially described as a new species in 1860 by Albert Günther, who named it Herpetodryas biserialis, a snake "light brown with a dark brown dorsal band" and having "maxillary teeth...of moderate size,...nearly equal length,...and entirely smooth". In 1912 John Van Denburgh, Curator of the Department of Herpetology at the California Academy of Sciences, wrote a monograph on the snakes of the Galápagos as part of a report on an expedition taken by the Academy in 1905-06. In it, he gave what is still the most complete account of the snakes' (by then moved to the genus Dromicus) natural history and ecology, and described four additional species (one of which was later synonomized with an earlier description by Austrian biologist Franz Steindachner). In accordance with the prevailing geologic thinking of the day, Van Denburg suggested that the snakes, along with the other Galápagos fauna, had reached the Galápagos via a land bridge, rather than by oceanic dispersal.

Plate from Steindachner 1876

Galápagos racers mating

Today these five species are known as Pseudalsophis biserialis (which occurs in two phases, dark and light, and is found on most islands), P. dorsalis (which is striped and found on Santiago, Rábida, Baltra, Santa Cruz, and Santa Fé), P. hoodensis (which is striped and found only on Gardner and Española, formerly known as Hood Island), P. slevini (which is banded and found on Fernandina, Isabela, and Pinzón), and P. steindachneri (which is striped and found on Santiago, Rábida, Baltra, and Santa Cruz). One interpretation is that these five species comprise a clade closely related to the mainland species P. elegans, found in Ecuador and Peru and supporting Bibron's suggestion via Darwin that Galápagos racers are related to and descended from mainland snakes. Variation in pattern and scalation is present but relatively minor. Another is that there were two independent colonizations of the Galápagos by South American snakes: one by Philodryas chamissonis from Chile (this is Bibron's Psammophis temminckii) that gave rise to P. hoodensis, and the other, by P. elegans, responsible for the other species. Others have suggested that P. slevini and P. steindachneri are descended from one ancestor (possibly a species of Antillophis from the Caribbean), P. hoodensis from another (P. chamissonis), and P. biserialis and P. dorsalis from yet a third (P. elegans, which might have invaded more than once). These hypothesized dispersal pathways are similar to those suggested for Tachysphex wasps from Chile, Microlophus lizards from Peru, and shrubs of the family Nolanaceae from Peru and Chile.

A Galápagos Snake among some Marine Iguanas

To me, the first explanation seems the most parsimonious; that is, it is simplest to assume that all snakes on the Galápagos archipelago are descended from a single ancestor (P. elegans), and this is what the most up-to-date taxonomy reflects. Similarities in ecology might account for the morphological similarities that led earlier herpetologists to suggest Chilean and Caribbean ancestry. Although on some islands multiple species are found, this could be explained by multiple movements among islands of the archipelago following clonization and subsequent speciation. A 2008 review by University of Texas evolutionary biologist Christine Parent and her colleagues found that most of the Galápagos terrestrial fauna with known phylogenies (family trees), such as tortoises and finches, have diversified in parallel with the geological formation of the islands, supporting the idea that they colonized the islands only once. Because no detailed molecular phylogeny is available for Galápagos snakes, the final answer to the question of their origin and relationships has not yet been revealed.

Galápagos snake eating a small iguana

I was surprised to find how poorly known these snakes were given the infamy of the islands they inhabit. Because they are probably important predators on Galápagos finches, mockingbirds, and small lizards, as well as on non-native rodents, they deserve more study (although as Nick has pointed out, permission to study animals in the Galápagos can be difficult to obtain). Along with many of the Galápagos' other reptiles and birds, the snakes were probably almost driven to extinction by introduced cats and rats, against which they had not evolved defensive behaviors. Their natural predators probably include Galápagos mockingbirds. Today, tourism and development, although limited in the Galápagos, probably threatens these snakes as much as invasive species, which are beginning to be brought under control. Nick, Lori, and Susannah are busy studying the effects of tourism on the Marine Iguanas - who is studying the Galápagos snakes?

Even in the Galápagos, snakes are not immune to vehicular manslaughter

ACKNOWLEDGMENTS

Special thanks to Nick Kiriazis for inspiring me to write this article with his blog, and thanks to Lori Neuman-Lee, Manuel Mejia, Dave Irving, Jim Moulton, Rosalind Gomes, and Phillip Marsh for their pictures.

REFERENCES

Grehan J (2001) Biogeography and evolution of the Galápagos: integration of the biological and geological evidence. Biol J Linn Soc 74:267-287 <link>

Günther A (1860) On a new snake from the Galápagos islands. The Annals and Magazine of Natural History 3:78-79

Parent CE, Caccone A, Petren K, 2008. Colonization and diversification of Galápagos terrestrial fauna: a phylogenetic and biogeographical synthesis. Philosophical Transactions of the Royal Society B: Biological Sciences 363:3347-3361 <link>

Steindachner F (1876) Die schlangen und eidechsen der Galapagos-inseln. Zoologisch-botanischen Gesellschaft, Wien, Germany. <link>

Thomas R, 1997. Galápagos terrestrial snakes: biogeography and systematics. Herpetol Nat Hist 5:19-40 <link>

Van Denburgh J (1912) Expedition of the California Academy of Sciences to the Galapagos Islands, 1905-1906. IV. The snakes of the Galapagos Islands. Proceedings of the California Academy of Sciences (Series 4) 1:323-374 <link>

Zaher H, Grazziotin FG, Cadle JE, Murphy RW, Moura-Leite JC, Bonatto SL, 2009. Molecular phylogeny of advanced snakes (Serpentes, Caenophidia) with an emphasis on South American Xenodontines: A revised classification and descriptions of new taxa. Pap Avulsos Zool (Sao Paulo) 49:115-153 <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.

The Unusual Soft Anatomy of Snakes

This year I had the opportunity to help my friend Lori Neuman-Lee dissect a number of Wandering Gartersnakes (Thamnophis elegans) for her research on the effect of toxic chemicals on reptile physiology. During my Master's, I had the opportunity to help teach a Comparative Anatomy course, during which I learned a great deal about the internal anatomy of vertebrates. However, dissecting an animal for research requires greater accuracy and precision than dissecting for teaching, and we decided to read up on snake anatomy before we got started. Because we found few resources to aid us in our work, we video-taped one of the dissections to help future would-be snake anatomists locate and identify snake organs, several of which can be a little tricky. Check out the video below and learn to dissect a snake! Lori is doing the dissection in the video, and like many things, she makes it look easy. I would recommend some pretty intense practice first if you want to become as accomplished as she is. Salvaged, all-too-common road-killed specimens often make for ideal practice if you don't mind bits of them being smashed, and they sometimes have interesting things in their stomachs.

A few notes: Snakes are long - it's in the blog title. But the implications of being long for the internal anatomy of an animal are not usually considered. For example, in humans and most other animals, paired organs, such as kidneys, lungs, and gonads, are found next to one another, across the body's plane of symmetry. This is not so in snakes; there simply isn't room. Add to their body shape the fact that a great deal of the body cavity must sometimes be filled with eggs or prey items, and there's little room left for the vital organs: heart, lungs, liver, kidneys, spleen and pancreas. That's why snakes have A) evolved elongate organs, B) evolved staggered paired organs, and C) lost some organs or members of paired organs.

Many snake organs are similar in shape to their overall body form. The liver, stomach, gonads, kidneys, and lung are all elongate. Those that come in pairs are either staggered, such as the kidneys and gonads (right always anterior to left), or asymmetrical, such as the lungs. See the tiny left lung near the heart? In a real snake it's almost impossible to find. It is a vestigial organ, meaning it does not function in breathing any more, although in some sea snakes it does have a co-opted function: it helps regulate buoyancy much like the swim bladder of a fish. These adaptations are part of what makes snakes so amazing and unique.

Finally, because 2013 has been designated the Year of the Snake by non-profit conservation group Partners in Amphibian and Reptile Conservation, I hope to help them promote snake research and snake conservation through frequent writing and outreach. As always, thanks for your comments and your readership. Life is Short but Snakes are Long received over 22,000 hits in 2012 and I'm looking forward to an even bigger 2013!

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

Magnificent Meizodon

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It isn't often that I'm sent a photo of a snake that I can't identify, but last week Alvaro Pemartin found the time both to finish translating all of my old blog posts into Spanish (many thanks to him!) and to obtain photographs of a snake that I had never heard of before. When he sent them to me, I was struck by how beautiful and distinctive the snake was, and it turned out to be quite difficult to identify. I shouldn't have been surprised, because it is from a herpetologically-poorly-known region of the world, western Africa. Alvaro works as a doctor in Guinea, and his nurse, Sandrine Chabassieu, photographed the snake as it crawled across their porch one day.

The mystery snake

Although Kate Jackson's new key to identifying snakes of western and central Africa is a great tool, we couldn't use it to identify this snake because we didn't have close-up pictures of the all-important scale characters that can be indispensable in identifying species of snakes. The backup method, sending the photos to as many people who might know as possible, eventually proved effective when Laurent Chirio, of the Muséum National d'Histoire Naturelle in Paris, France, wrote me that "This is without any doubt a beautiful Meizodon coronatus. I found some specimens with this kind of colour pattern in Guinea."

I wanted to learn what I could about this snake, because it was so striking and previous unknown to me. There isn't a lot out there. Meizodon coronatus, also known as the Western Crowned Snake, is one of five species in Meizodon, a genus of poorly known colubrine snakes found in sub-Saharan Africa. Western Crowned Snakes are found from Senegal to the Congo along the coast of western Africa, while the other four species are found in eastern and central Africa. The Western Crowned Snake was the first species of Meizodon described, by Hermann Schlegel in 1837, who called it Calamaria coronata in his first major published work (Essai sur la Physionomie des Serpens) as assistant curator of the Natural History Museum of Leiden in the Netherlands. The species was later moved to Coronella (subgenus "Mizodon") by Giorgio Jan of the Milan Museum in 1866, then placed in Meizodon in 1955 by Arthur Loveridge.

Plate from Jan 1866

No genes of any species of Meizodon have been sequenced, so it's difficult to say exactly how they are related to other snakes, but if their placement in Colubrinae is correct, then they are probably closely related to other west African species of colubrine, such as the egg-eating Dasypeltis and wolf-toothed Lycodon. These snakes are descended from the same common ancestor as North American kingsnakes and ratsnakes, from which they diverged about 33 million years ago.

Another of Sandrine's photos

Meizodon are primarily predators of lizards, especially skinks, although they are also known to eat geckos, small mammals, and frogs. They are not as specialized for feeding on skinks as their relatives the wolf snakes (Lycodon), on which an upcoming article will focus, but their genus name describes their teeth, which increase in robustness toward the back of the jaw. Meizodon coronatus seem to be a diurnal foragers. A few individuals were observed foraging along the base of a crumbling wall by Godfrey Akani and colleagues at Rumueme, Nigeria. These snakes probed with their heads into holes and crevices where geckos and other lizards were sleeping. Typically, Meizodon are apparently found in refugia such as under rocks, within hollow trees, and underneath loose bark during the day. Don Broadley of the Zimbabwe Natural History Museum  recalls capturing several Meizodon semiornatus that were sheltering inside tree hollows in a flooded forest in western Botswana, along with the psammophine snakes Psammophylax and Psammophis. Broadley noted that several snakes were sometimes captured per tree, including evidence of shed skins and skeletons, although these observations might be atypical given the flooded nature of the forest at the time of Broadley's visit.

The best of Sandrine's photos, in my opinion, showing the gorgeous anterior pattern.

Likely viviparous, Meizodon coronatus inhabits savannahs, forests, plantations, and urban areas. They are mentioned in a study conducted by Godfrey Akani and colleagues on anthropogenic causes of snake mortality in west African suburbs. They found that anthropogenic snake mortality in suburbs of southeastern Nigeria were about 50% intentional, 50% unintentional (e.g., roadkills, snares set to trap more edible wildlife), and that more snakes were killed in the wet season, when they are presumably more active. Even though most of the snake species in this region are harmless and beneficial to humans (in that they exert strong top-down control on populations of pesty rodents, by eating them), most people did not know how to differentiate venomous from non-venomous snakes. It's interesting to know that some ecological problems are common to places as different as North America and Africa. I was glad to hear from Alvaro and Sandrine that, now that they know their beautiful snake is a harmless Meizodon, they have encouraged their camp guards not to kill other Meizodon they might see in the future.

M. coronatus from Cameroon. Not nearly as striking as the one from Guinea.

Edit: 4-Dec-2019: In response to a claim that Meizodon are opisthoglyphous, I revisited some of the literature and found that the original description of Meizodon coronatus by Schlegel in 1837 states (p. 47):

Elle a les dents toutes d'égale longueur ("The teeth are all of equal length")

Günther (1860, p. 429) wrote of M. coronatus that:

The maxillary teeth form one continuous series; anteriorly small, they gradually become longer and stouter posteriorly; none of them are grooved.

Fischer's (1856) original description of M. regularis reads:

Oberkiefer mit 18-19 Zähnen; die ersten sind sehr klein, dicht gedrängt; sie werden nach hinten etwas grösser und weitläuftiger, so dass die letzten doppelt so gross sind als die ersten; ohne Lücken, Keiner derselben ist gefurcht. Unterkiefer mit 20-22 Zähnen, von denen die ersten wenig grössen sind als die letzten, und nach hinten allmählich an Grösse abnehmen. Gaumenzähne: Palatini 12, pterygoidei 14-16, die letzten schwach nach innen gekrümmt (Upper jaw with 18-19 teeth; the first ones are very small, densely crowded; they become slightly larger and wider towards the back, so that the last ones are twice as big as the first ones; without gaps; none of them are grooved. Lower jaw with 20-22 teeth, of which the first are slightly larger than the last, and gradually decreasing in size towards the back. Palatine teeth: 12, pterygoid teeth 14-16, the last teeth slightly curved inwards)

Although the genus name Meizodon comes from the Greek words meizo ("larger" or "greater") and -don (from odonto = "tooth"), this seems to refer to a gradually increasing series rather than an enlarged rear tooth or pair of teeth. I was only able to find a single illustration of the teeth of these snakes (here and above; reprinted from Jan 1866 as part of a detailed comparison of M. regularis and M. coronatus written in 1969). Although there are opisthoglyphous colubrine colubrids (e.g. Dispholidus, Thelotornis) that can kill humans, most species, even those with enlarged rear teeth, do not possess venom dangerous to humans (although colubrid venom and its relationship to tooth anatomy is still on its way to becoming well-understood). Eventually the skull of a Meizodon will be CT scanned & posted here, but until then the single drawing from 1866 and the written descriptions are all we have to go on.

ACKNOWLEDGMENTS

Thanks to Alvaro and Sandrine for the photos, and to Pierson Hill, Peter Uetz, and Laurent Chirio for nailing the ID.

REFERENCES

Akani G, Eyo E, Odegbune E, Eniang E, Luiselli L (2002) Ecological patterns of anthropogenic mortality of suburban snakes in an African tropical region. Isr J Zool 48:1-11 <link>

Barbault R (1976) Population dynamics and reproductive patterns of three African skinks. Copeia 1976:483-490 <link>

Böhme W (2000) Diversity of a snake community in a Guinean rain forest (Reptilia, Serpentes). Bonn Zool Monogr 46:69-78

Broadley DG (1988) Meizodon semiornatus semiornatus: Semiornate Snake. Habitat, Diet, and Distribution. The Journal of the Herpetological Association of Africa 34:44

Günther A (1860) On a West-African genus of snakes (Meizodon). Proc Zool Soc Lond 28:427-430

Jan G (1866) Iconographie Générale des Ophidiens. Livraison. J.B. Bailière et Fils, Paris <link>

Luiselli L, Akani GC, Angelici FM (2001) Diet and foraging behaviour of three ecologically little-known African forest snakes: Meizodon coronatus, Dipsadoboa duchesnei and Hapsidophrys lineatus. Folia Zool 50:151-158

Schlegel H (1837) Essai sur la physionomie des serpens. Partie descriptive. Kips and Van Stockum, La Haye

Segniagbeto GH, Trape JF, David P, Ohler A, Dubois A, Glitho IA (2011) The snake fauna of Togo: systematics, distribution and biogeography, with remarks on selected taxonomic problems. Zoosystema 33:325-360

Roux-Estève, R. 1969. Étude comparée de Meizodon coronatus (Schlegel) et de Meizodon regularis Fischer (Colubridés - Serpentes). Bull. Mus. Natl. Hist. Nat. Paris (ser. 2) 41: 395-409

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