Monday, March 16, 2015

Rattlesnake Roundups

This post will soon become available in Spanish

Eastern Diamondback Rattlesnake (Crotalus adamanteus),
the world's largest species of rattlesnake (maximum 8'3")
Rattlesnakes are one of North America's most iconic symbols. I think of them as herpetological Bald Eagles, only more diverse. Our continent boasts all 41 species, from huge diamondbacks to tiny pygmies, all of which diversified from a common ancestor 10-20 million years ago. Both American Indians and America's founding fathers viewed rattlesnakes as symbols of independence and strength, and new research is revealing that they are among the most social and behaviorally complex of snakes, caring for their young and displaying signs of spatial awareness and self-identity. Large species may take as long as ten years to become sexually mature, reproduce only once every three years in the northern part of their range, and live up to 30 years. Although many people fear rattlesnakes, comparatively speaking you are more likely to be bitten by a dog, struck by lightning, killed by office supplies, by your pajamas, or by just about anything other than a venomous snake in the USA. However, numerous communities in Alabama, Georgia, Kansas, New Mexico, Oklahoma, and Texas [Edit: Melissa Amarello of Advocates for Snake Preservation tells me that the Kansas & New Mexico roundups have been discontinued since 2007 for economic reasons.] carry out annual rattlesnake roundups, events with the purpose of exterminating wild rattlesnakes from the landscape.

Western Diamondback Rattlesnake (Crotalus atrox),
the species targeted by most roundups these days
Wholesale slaughter of rattlesnakes and other venomous snakes is nothing new. Already in 1750 the Swedish naturalist Pehr Kalm observed that "Formerly there were large numbers of these snakes in New Sweden as well as in other parts of North America now occupied by Europeans; however, they have nearly been exterminated." The first recorded bounties were paid to rattlesnake hunters in the 1680s in Masssachusetts. At first, communities and informal groups organized roundups in an attempt to improve public safety—although whether rounding up and killing rattlesnakes actually accomplishes this goal is debatable. Financial gain was not the purpose of early roundups, because the rattlesnakes themselves were considered worthless. In the 1950s, civic organizations such as fire departments, Jaycees, Kiwanis, and the Lions Club took on the role of organizing roundups, which became larger and began to gain more commercial potential; people would pay to attend and would support vendors by buying rattlesnake products. Modern roundup organizers are primarily motivated by raising money for their local community or for charity, and rattlesnake roundups are now more similar in nature to other public events, such as county fairs or rodeos. Most include other events, including occasional educational programs and/or daredevil shows, as well as music, dances, beauty pageants, and carnival rides (some to the point where the rattlesnakes are more of a sideshow, such as the case of the roundup in Freer, Texas). The population of the small communities where these events occur can increase tenfold during roundups, and millions of dollars can enter the local economy, only a small percentage of which come directly from the sale of the rattlesnakes. As a result of geography, competition among one another for visitors, and declining demand and prices for dead rattlesnakes, 36 of the 47 rattlesnake roundups in Texas closed their doors between 1991 and 2006. Texas state laws have also increased the requirements for hunting rattlesnakes, requiring a costly non-game permit and prohibiting collecting snake on roads, and high gas prices have made the costs of hunting snakes over wide areas prohibitive, as many herpers know.

Western Rattlesnake (Crotalus oreganus), the species
by which most Americans are bitten—about 1,500 a year1
In the past, rattlesnakes gathered for roundups were shot, stomped, buried, or otherwise wasted. Now, at the Texas roundups that remain, all parts of the rattlesnake are used: the venom is ostensibly sold for antivenom production and medical research2, the meat cooked and eaten, often right there at the roundup, the rattles, heads, and skins made into curios and souveniers, the gall bladders are sold to a growing Asian-American market, and the remaining guts are used for fish bait. It's likely that the incentive to amass live, healthy rattlesnakes of commercial value has reduced the amount of cruel and inhumane treatment that the snakes suffer, although snakes subjected to the exploitative and sensational daredevil contests or otherwise manhandled for the amusement of the public are certainly not treated ethically, and I doubt such behavior would be tolerated if its target were any other kind of animal.

Dead snakes, mostly homalopsids, for sale at a market in
Indonesia. One cylindrophiid is visible in the upper right.
Photo by Nurcholis Anhari Lubis, National Geographic.
At a broader scale, the economic incentives associated with rattlesnake roundups might also provide incentives for communities to "manage" their local rattlesnake populations and prevent their extinction. Is it possible that rattlesnakes might one day be regulated as a game species and managed, as we manage deer, turkey, quail, and so many other species? Probably not, unfortunately—it is extremely difficult to know how many snakes are in an area, because mark-recapture techniques used for other wildlife are hampered by the low detection probably of individual snakes. As a result, state DWRs aren't very likely to try to manage snakes as game species, even though western diamondbacks in Texas effectively are one, because are traded and have a market value, at roundups and also outside of them. New techniques for monitoring snakes and programs to enhance management efforts for non-game wildlife, such as State Wildlife Action Plans, could help bring about this change. It's an approach that has worked for crocodilians, which are harvested for their meat and skins, and it might be needed to help regulate the billion-dollar global snake trade for food, skins, and pets, particularly in light of emerging markets in southeast Asia. Even some wildlife biologists are reluctant to view venomous snakes as wildlife rather than as pests, and as a result the responsible management of venomous snakes is lacking. For instance, in Georgia there are essentially no restrictions on the harvest of non-threatened "poisonous" snakes, whereas non-venomous snakes and most other non-game wildlife are protected. It might be beneficial if we started managing more herps as game rather than non-game, if only because more people would care if they disappeared. If state wildlife agencies mandated that rattlesnake hunters mark and release a certain portion of their catch, and those hunters hunted the same areas every year and at the same time of year (which already happens), and the same effort were put forth in control areas where no snakes were removed, then a real monitoring program could be built. A modeling exercise showed that a minimum size limit could protect most females, improve hunter profits, and has the potential to result in a sustainable harvest, particularly in the southern part of Texas where western diamondbacks and their populations likely grow rapidly.

Timber Rattlesnake (Crotalus horridus), the species whose
former range overlaps with the most densely-populated areas
of the USA. Even so, most people will never see one.
Evidence from roundup reports suggests that rattlesnake roundups in Alabama & Georgia are indeed negatively affecting populations of eastern diamondbacks, whereas limited evidence suggests that those in Texas and New Mexico [Edit: The New Mexico roundup is now defunct.] might not be affecting western diamondback populations quite so much—the average number of western diamondbacks brought to the Sweetwater roundup (about 2,900; range 800-9,700) did not decrease between 1959 and 20063. It's likely that Timber Rattlesnake roundups in Pennsylvania were once quite harmful, considering the extent of habitat development throughout the range of this species and its reliance on a limited number of communal dens, but a Pennsylvania state law has prohibited the killing of native venomous snakes since the 1970s4. Certainly different species of rattlesnakes respond differently to harvest; some are more fecund than others, and differences in lifespan, age at maturity, and biological interactions also play a role. A survey showed that many roundup organizers and rattlesnake hunters believe that roundups do not harm rattlesnake populations, but they also paradoxically think that removing rattlesnakes from land does protect humans, pets, and livestock from rattlesnake bites. In reality, the ecological effects of removing predators are as unknown and controversial as ever. Ecological research has shown that predator control does not always accomplish what people think it does. The ecological effects of pumping gasoline fumes into rattlesnake burrows and dens in order to evacuate the residents (which is how the majority of rattlesnakes brought to roundups are collected) are also unclear, although it's hard to imagine that they aren't negative. As for the claim that rattlesnake roundups prevent snakebite, there is little to no data to support or refute this claim, but I find it very hard to conclude that this is true. Snakebite in the USA is already so exceedingly rare that any reduction in its incidence would be almost impossible to detect, and fine-scale data to assess the rate of snakebite in the areas hunted for rattlesnake roundups do not exist. Bill Ransberger, a rattlesnake handler from Sweetwater, says he has been bitten 42 times by rattlesnakes since 1958, a number that represents about one-twentieth of one percent of all the rattlesnake bites in the USA during that time period. There really is no way to evaluate the number of snakebites caused or prevented by rattlesnake roundups.

Active since 1971, in 2012 the Evans County Wildlife Club
decided to discontinue their annual rounding-up of wild
rattlesnakes and now hosts the Claxton Rattlesnake Festival,
which features live captive rattlesnakes which are provided by the
Georgia DNR and displayed but not killed. I took this photo
along Interstate 16 in Georgia in 2009.
All told, habitat destruction and fragmentation are probably worse for rattlesnakes than roundups, although actual estimates of the effects of either on rattlesnake populations are scarce and fraught with uncertainty. The destruction of rattlesnakes at roundups or by other means has probably never benefited livestock or grazing lands or human safety or "the balance of nature". The educational messages at roundups, if they exist, are mostly ones of "bad environmental science and senseless risk-taking". However, it's hard to deny that the roundups, particularly Sweetwater, have become symbols of community identity, publicity extravaganzas, and boons to struggling local economies. Today, between 17 and 25 roundups exist in towns in seven states [Edit: four states: Texas (10), Oklahoma (5), Georgia (1), and Alabama (1); five states if you count the 8 catch-and-release events in Pennsylvania]. Whether these events transform into more positive, respectful events, or wither and die, probably has more bearing on the future of the communities that host them than on the future of rattlesnakes. But, in keeping with the theme that wildlife-human interactions ought to be more respectful than they are, foresightful roundup organizers might want to imitate those in Georgia and Pennsylvania by beginning to shift the focus of their events towards conserving and learning more about native wildlife, perhaps by focusing on finding rattlesnakes in order to contribute data about them to citizen science programs. It's time we start treating rattlesnakes with the poise and dignity with which they treat us.

If you'd like to encourage the remaining rattlesnake roundups to reform, sign this petition, join Rise Against Rattlesnake Roundups, and attend one of these events: 
If you're aware of other reformed rattlesnake roundups or events that portray venomous snakes in a positive way, please let me know in the comments!

1 It's tough to estimate this number because not all snakebites are reported and the species is not reported or may be incorrectly identified in all reported snakebites. To get 1,500, I used data from southern California suggesting that 80-90% of snakebites in that region are from C. oreganus, and extrapolated to the figures reported in the most recent review that ~4,700 human exposures to native venomous snakes occur each year, about half of which are to rattlesnakes. I assumed that half of the 48% of bites from unidentified venomous snakes were also from rattlesnakes. Although the actual figure might be anywhere from 1,000 to 2,000, I'm fairly confident that C. oreganus is the species of rattlesnake by which most Americans are bitten every year, because it's among the most common and widespread. Probably slightly more people are bitten by Copperheads (Agkistrodon contortrix) each year.

2 Herpetologists and physicians claim that venom collected at roundups is unsuitable for use in the manufacture of antivenin, because it is not sterile. Both venom dealers and antivenom producers are quite guarded about the sources that they use, so it is difficult to evaluate this claim or that made by the organizers of rattlesnake roundups that the venom that they collect is put to some useful purpose.

Data from Adams & Thomas 2008 (p.69)

3 Interviews conducted by the same authors found that claims that area hunted has increased or that roundups are importing snakes from far away to sustain themselves are apparently unfounded (except, see the Pennsylvania comment below). At least, snake hunters at Sweetwater and other Texas roundups reported hunting the same dens year after year, and the lower prices paid per pound of snake (see graph) suggest that importing snakes or hunting them over a wider range is not a viable economic strategy. In 1991, 83 of 111 Texas counties within the range of the western diamondback were hunted for roundups, with much of the effort clumped around the communities holding the roundups and at dens adjacent to roads, because the equipment used for pumping gasoline fumes into dens is heavy. It's likely that much less of this land is hunted today, given the number of roundups that have shut down, new TX state laws prohibiting the collection of any snakes from roads, the increased price of gas, the decreasing price of rattlesnake meat & skins, and liability concerns of landowners.

4 It seems that most Pennsylvania roundups have converted to catch-and-release events as per Pennsylvania state law, while a minority import (and kill, and eat) a limited number western diamondbacks from the southwest each year. The state legislature is reluctant to ban the events completely, as they are mainstays of firehouse fund-raisers in almost a dozen rural communities, but they have instituted bag and size limits and a two-day season, restricted collection to male snakes, and mandated that all snakes be marked and released where they were captured (although enforcement is understandably quite challenging). [Edit: Melissa Amarello helped me confirm the truth of this.]


Thanks to Dave Irving, Rich, Augustus Rentfro, and Nurcholis Anhari Lubis for the use of their photographs.


Adams, C.E. and J.K. Thomas. 2008. Texas Rattlesnake Roundups. Texas A&M University Press, College Station, Texas <link>

Adams, C.E., J.K. Thomas, K.J. Strnadel, and S.L. Jester. 1994. Texas rattlesnake roundups: Implications of unregulated commercial use of wildlife. Wildlife Society Bulletin 22:324-330 <link

Campbell, J.A., D.R. Formanowicz Jr, and E.D. Brodie Jr. 1989. Potential impact of rattlesnake roundups on natural populations. Texas Journal of Science 41:301-317. 

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

Clark, R.W., W.S. Brown, R. Stechert, and H.W. Greene. 2012. Cryptic sociality in rattlesnakes (Crotalus horridus) detected by kinship analysis. Biology Letters 8:523-525 <link

Douglas, M.E., M.R. Douglas, G.W. Schuett, and L.W. Porras. 2006. Evolution of rattlesnakes (Viperidae; Crotalus) in the warm deserts of western North America shaped by Neogene vicariance and Quaternary climate change. Molecular Ecology 15:3353-3374 <link

Fitch, H.S. 1998. The Sharon Springs Roundup and prairie rattlesnake demography. Transactions of the Kansas Academy of Science 101:101-113 <link

Fitzgerald, L.A. and C.W. Painter. 2000. Rattlesnake commercialization: Long-term trends, issues, and implications for conservation. Wildlife Society Bulletin 28:235-253 <link/full-text

Larsen, E.L. 1957. Pehr Kalm's Account of the North American Rattlesnake and the Medicines Used in the Treatment of its Sting. American Midland Naturalist 57:502-511 <link

Means, D.B. 2009. Effects of rattlesnake roundups on the Eastern Diamondback Rattlesnake (Crotalus adamanteus). Herpetological Conservation and Biology 4:132-141 <link

Mushinsky, H.R. and A.H. Savitzky. Position of The American Society of Ichthyologists and Herpetologists Concerning Rattlesnake Conservation and Roundups <link

Reber, D.L. and A.S. Reber. 1994. Kansas Herpetological Society position paper regarding rattlesnake roundups <link

Seifert, S.A., L.V. Boyer, B.E. Benson, and J.J. Rogers. 2009. AAPCC database characterization of native U.S. venomous snake exposures, 2001-2005. Clinical Toxicology 47:327-335 <link

Speake, D.W. and R.H. Mount. 1973. Some possible ecological effects of "rattlesnake roundups" in the southeastern coastal plain. Pp. 267-277 27th Annual Conference of the Southeastern Association of Game and Fish Commissioners <link

Thomas, J.K. and C.E. Adams. 1993. The social organization of rattlesnake roundups in rural communities. Sociological Spectrum 13:433-449 <link

Weir, J. 1992. The Sweetwater Rattlesnake Round‐Up: A Case Study in Environmental Ethics. Conservation Biology 6:116-127 <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.

Saturday, February 28, 2015

Anilius: The Pipesnake that Wasn't

This post will soon be available in Spanish

Anilius scytale, the only living member of the family Aniliidae,
one of only two snake families containing just a single species
Deep in the Amazon rain forest there lives a fairly small, fairly obscure, red and black snake called Anilius scytale. It is banded, like many red and black snakes, but it has no venom, so it may be a coralsnake mimic. It spends most of its time under ground or in the water. Morphologically, it has a mixture of characteristics that place it somewhere in the no-man's-land we call "henophidia"—it has pelvic vestiges like many boas and pythons, but it has a small gape and is not capable of eating large bulky prey. It mostly feeds on elongate vertebrates, including other snakes, amphisbaenians, caecilians, and eels, and like other snake-eating snakes individuals can eat prey approaching their own total length. Its ventral scales are only barely wider than its dorsal scales, and it has just a few enlarged head scales, including one large hexagonal scale covering the eye and the surrounding skin. Males are smaller than females, which are viviparous, capable of giving birth to as many as 24 live young at a time. In 1946, the great naturalist William Beebe wrote "This is a strange snake", meaning that it's not quite like any other snakes. It is alone in its family, Aniliidae.

Head of Anilius showing the large scale covering both
the eye and the surrounding skin, like blindsnakes but
unlike most heno- and caenophidians
Snake biologists have used the term "pipesnake" to refer to any of three different lineages of snakes: the cylindrophiids (10 species of "Asian pipesnakes"), anomochilids (3 species of "dwarf pipesnakes"), and aniliids (1 species of "red pipesnake"; i.e., Anilius scytale). I'd like to propose that we begin to think of Anilius as "the pipesnake that wasn't", because (as I alluded to last month), it is now thought to be most closely related to tropidophiids (aka "the boas that weren't), superficially boa-like snakes found mostly in the Caribbean. Molecular data and some morphological data, especially that of the soft anatomy of the lungs and reproductive system, suggests that these two groups are each others' closest relatives, and they are now placed together in the Amerophidia (aka Anilioidea), the basal-most lineage of alethinophidia, which was apparently isolated in South America during the split-up of west Gondwana. Details of the skull anatomy cast some doubt on this classification, suggesting a closer relationship between aniliids and other non-macrostomatan pipesnakes, although even if this is true there are undoubtedly deep splits between Anilius and any other living snakes. Like the tuatara and the coelacanth, Anilius has not had close living relatives for tens of millions of years. Only it knows if it's lonely out there on such a long branch of the snake family tree.

Top: The plate of Anilius and a caiman as it appeared in
the 1719 printing of Merian's Metamorphosis
Insectorum Surinamensium

Bottom: A later version of the plate,
recolored and with the eggs removed
If Anilius is lonely, it can take some solace from having been noticed and beautifully illustrated by one of the first ecologists, Maria Sibylla Merian. Merian was a remarkable artist and scientist who lived from 1647 to 1717. She was one of the first trained artists to conduct detailed, long-term studies of living organisms, and the first published female naturalist. Most of her drawings, which she sketched from life on vellum and later engraved herself on copper plates, depict the life cycles of insects and their plant hosts, which she raised in captivity. She was the first to document that caterpillars turned into butterflies, and she described the life cycles of hundreds of insects, amassing evidence that contradicted the then-widespread notion that insects were "born of mud" by spontaneous generation (although others were credited with this discovery for a long time because her work was largely ignored, because it was written in Dutch rather than Latin). In 1699, Merian and her fifteen year-old daughter traveled to Surinam, where they spent the next two years studying and drawing the indigenous animals and plants, including several snakes. Her most famous work, Metamorphosis Insectorum Surinamensium, contains plates of many of these snakes, including one of an Anilius eating the egg of a caiman and being simultaneously attacked by the adult crocodilian. Like most of her drawings, it shows aspects of the natural history and ecology of the organisms in it, and helped establish a style of scientific illustration that later inspired naturalists from Catesby to Audubon. She depicted most of her insects life-sized, from various angles, in all stages of their life cycles, and most importantly, interacting with their host plants and predators. Her observations of animal behavior and plant-animal interactions are so detailed that many consider her the first ecologist. Considering that she died when Linnaeus was only 10 years old, it is all the more remarkable that her writings and drawings emphasize where organisms live and what they do rather than how they should be classified. Her works became very popular among Europe's upper class, and Czar Peter the Great in particular purchased many of her original watercolors and recruited her daughter as an art advisor and teacher at the newly-founded Academy of Arts in St. Petersburg. The Argentine Black and White Tegu, Tupinambis merianae, is named after her. Merian's text has not been translated into English, but I have taken a stab at translating her paragraph about snakes here:

Like crocodiles, some snakes hatch from eggs. They lay many small ones. The head and the tail of this snake, the Amphisbona, are the same shape and size, but you can tell which is the head because it has a mouth and small eyes, whereas the tail does not. Of all snakes, this one is the cleanest in color, being black, red, and yellow; others are grayish white, yellow, and brown with bodies that are more flattened.


Thanks to Patrick Campbell and Andrew Snyder for allowing me to use their images.


Anilius from d'Orbigny's 1849 Dictionnaire
Universel d'Histoire Naturelle
Beebe, W. 1946. Field notes on the snakes of Karatabo, British Guiana, and Caripito, Venezuela. Zoologica 31:11-52.

Duellman, W.E. 1978. The biology of an equatorial herpetofauna in Amazonian Ecuador. Miscellaneous Publications, Museum of Natural History, University of Kansas 65:1-352 <link>

Etheridge, K. 2011. Maria Sibylla Merian: The First Ecologist. in V. Molinari and D. Andreolle, editors. Women and Science: Figures and Representations – 17th century to present. Cambridge Scholars Publishing, Newcastle upon Tyne <link>

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

Martins, M. and E. M. Oliveira. 1998. Natural history of snakes in forests of the Manaus region, Central Amazonia, Brazil. Herpetological Natural History 6:78-150 <link>

Maschio, G. F., A. L. da Costa Prudente, A. C. de Lima, and D. T. Feitosa. 2007. Reproductive biology of Anilius scytale (Linnaeus, 1758) (Serpentes, Aniliidae) from eastern Amazonia, Brazil. South American Journal of Herpetology 2:179-183 <link>

Maschio, G. F., A. L. C. Prudente, F. S. Rodrigues, and M. S. Hoogmoed. 2010. Food habits of Anilius scytale (Serpentes: Aniliidae) in the Brazilian Amazonia. Zoologia (Curitiba, Impresso) 27:184-190 <link>

Merian, M.S. 1719. Metamorphosis Insectorum Surinamensium. Joannes Oosterwyk, Amsterdam <link>

Pieters, F. F. J. M. and D. Winthagen. 1999. Maria Sibylla Merian, naturalist and artist (1647-1717): a commemoration on the occasion of the 350th anniversary of her birth Archives of Natural History 26:1-18 <link>

Sawaya, R. J. 2010. The defensive tail display of Anilius scytale (Serpentes: Aniliidae). Herpetology Notes 3:249-250 <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.

Wednesday, January 28, 2015

Dwarf Boas

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

Ambergris Cay Dwarf Boa (Tropidophis g. greenwayi)
Now that the USA and Cuba are finally warming up to one another after a chilly fifty years, we might be poised to learn a lot more about a really interesting group of snakes that reach their highest diversity on Cuba. These are the tropidophiids, or "dwarf boas". Their name is a little misleading—like the splitjaw snakes, they were once thought to be related to the true boas, and the name sticks even now that we now know better. At least the dwarf part is accurate: most tropidophiids are only 1–2 feet long. But this unassuming group of drab, nocturnal, live-bearing snakes holds more surprises and lessons about snake evolution that one would expect at first glance, with no shortage of interesting natural history to boot.

Top: Tropidophis melanurus constricts an anole
From Torres et al. 2014
Bottom: Madagascar Ground Boa
(Acrantophis madagascarensis)
constricts an oplurid lizard
Tropidophiids eat mostly frogs and lizards, and they constrict their prey in the same way as true boas: by winding the anterior part of their body neatly around their prey like a rope around a windlass, usually with an initial twist in the first loop, so that the snake's belly faces its head. This behavior, along with their relatively large gape size, seemed to suggest that they were related to the true boas (family Boidaesensu stricto), including well-known tree boas, boa constrictors, and anacondas. All true boas are neotropical and there are quite a few in the West Indies, so unlike many of the other boid "hangers-on" (such as the Malagasy Sanzinia & Acrantophis, African Calabaria, North American rosy and rubber boas, Pacific Candoia, and Old World sand boas), a close relationship between tropidophiids and boids was easy to accept in terms of the biogeography of the living species. A comparative analysis of constriction behavior in extant alethinophidian snakes done by Harry Greene and Gordon Burghardt showed that this pattern of constriction is shared by essentially all "henophidian" snakes, including booids, pythonoids, and some uropeltoids, notwithstanding a few fossorial species that have apparently secondarily lost constriction behavior alltogether, because it doesn't work in tight spaces.1

Top: Panamanian Dwarf Boa (Ungaliophis panamensis),
a member of the group to which tropidophiids were
once thought to be most closely related.
Bottom: Red Pipesnakes (Anilius scytale)
don't resemble tropidophiids very closely,
but we now think that they are each others'
closest living relatives.
In particular, what we now call tropidophiids were thought to be particularly closely related to two other small genera of neotropical boids, Exiliboa and Ungaliophis, which they superficially resemble both morphologically2 and ecologially. These still share their common name of "dwarf boa", but about 15 years ago a new picture began to emerge. While DNA from Exiliboa and Ungaliophis suggested that they were indeed related to true boas, evidence from both mitochondrial and nuclear DNA and immunological proteins of Tropidophis and Trachyboa, along with details of their muscular, circulatory, and reproductive anatomy, suggested that they were most closely related to the monotypic family Aniliidae, which contains a single South American species known as the Red Pipesnake (Anilius scytale). As far as we know, Anilius doesn't normally constrict its prey3, because it mostly forages underground on elongate vertebrates such as eels, caecilians, amphisbaenians, and other snakes, similar to various Asian pipesnakes to which it was once thought to be closely related. But, we are now fairly certain that these Asian pipesnakes are convergent with Anilius, that tropidophiids and aniliids are each others' closest relatives, and that the similarity between the gape size and constriction behavior of tropidophiids and that of boas and pythons probably still represents the shared retention of a paired morphology/action pattern used by their common ancestor, it's just a common ancestor that is much older than we originally thought. Estimates suggest that tropidophiids and aniliids diverged from one another 60-110 mya in South America4, after their common ancestors were isolated from those of all other modern alethinophidian snakes, which radiated in Africa following the mid-Cretaceous split-up of west Gondwana 70-120 mya. This was the split that formed South America and Africa, and we are now getting used to diving the alethinophidians into two major lineages, Amerophidia (tropidophiids and aniliids) and Afrophidia (everybody else), instead of into a monophyletic "crown-group" Macrostomata containing boas, pythons, and caenophidians, and a basal group of non-macrostomatan pipesnakes more similar in ecology to scolecophidians. My snake taxonomy article from 2013 is actually out-of-date with respect to this major shift in snake taxonomy, because at the time it was still unclear to me (and there are still some strong arguments from paleontologists that the molecular data may be misleading).

The Greater Antilles, Bahamas, and Turks & Caicos
The "new" family Tropidophiidae consists of two species of "eyelash dwarf boas" in the mainland genus Trachyboa (there we go with the boa thing again), and the diverse genus Tropidophis, which contains 32 species in total: 5 from mainland South America, and a West Indian radiation consisting of 17 Cuban species (one of which is shared with Jamaica and one with both Jamaica and Hispaniola), 1 on Hispaniola (shared with Cuba), 5 on Jamaica (two shared with Cuba), 2 in the Bahamas, one from the Turks & Caicos Islands, one each on the three Cayman Islands (Grand Cayman, Little Cayman, and Cayman Brac), and one endemic to Navassa Island, a small, uninhabited, disputed island in the Caribbean Sea between Cuba, Jamaica, and Hispaniola (which is known from four specimens and has not been seen in over 100 years). The West Indian species, particularly the Cuban ones, represent a radiation which rivals and parallels that of Darwin's finches. Morphological and molecular data suggest that the 17 species on Cuba are descended from a single colonization event, and that the island species appear to be more distantly related to the mainland ones than they are to Trachyboa, although four-fifths of the species of Tropidophis have no published sequence data yet so both of those conclusions could change.

Tropidophis xanthogaster bleeding from the mouth,
with blood behind the spectacle making the eyes appear red.
From Torres et al. 2013
As early explorers and biologists collected these snakes from bromeliads, within stone walls, and underneath rocks, they noted that species of Tropidophis made no effort to escape their collection, but rather coiled up into tight balls when captured. Another peculiar defensive behavior was soon noted—autohemorrhage of the nose and mouth. In other words, these snakes spontaneously bleed from these orifices and smear the blood all over themselves when handled. Creepily, the space between their spectacle and their eyes fills with blood momentarily beforehand, so that their eyes appear to flash red. Blood collected from their mouths doesn't clot for over half an hour, whereas blood collected simultaneously from their tails has clotted after 10 minutes, and the mouth blood is more acidic and has fewer red blood cells, presumably because it is mixed with saliva. However, it is not harmful to frogs or lizards, so it is not a substitute for venom. The exact function is unclear, but it appears to be to freak out would-be predators. Like many snakes, Tropidophis habituates to captivity and eventually does not exhibit this behavior.

Tropidophis melanurus, the largest species of Tropidophis
and the first described, from Cocteau & Bibron's 1843
volume on reptiles
in de la Sagra's Histoire physique, politique,
et naturelle de l’Ile de Cuba
Just when you thought things couldn't get any more interesting, brace yourself, because most Tropidophis can change color! They are light silver-white at night, when they are active, and dark grayish-brown during the day, when they are not. It takes a Tropidophis 1-2 hours to go from completely light to completely dark, which they accomplish via mobilization of melanosomes (organelles containing the light-absorbing pigment melanin) from the core of a melanophore cell deep within their skin into finger-like extensions of the melanophore that are closer to the surface of the skin, partially blocking stationary xanthophores and iridiophores, which contain yellow, blue, or green pigments. Both adults and juveniles undergo diel color change, and it does not seem to be affected by age, sex, pregnancy, or feeding, although prior to shedding snakes remain dark and inactive for several days. The change is probably predominantly triggered by photoperiod, but exposure to cool temperatures (<63°F) can elicit a partial change from dark to light even in the middle of the day. When captive snakes were transported from Cuba to Czechoslovakia, they became jet-lagged—it took them several days to synchronize their rhythm to the new photoperiod, and keeping them in complete darkness for several days desynchronized their rhythm from that of the sun. The proposed function of this color change is to help nocturnally-active snakes retain their body heat, as light-colored objects lose heat more slowly than dark-colored ones. This is probably similar to the reason that Round Island Splitjaw Snakes, Pacific Keel-scaled Boas (Candoia carinata), and the Hogg Island race of Boa constrictor also become lighter-colored at night.

Tropidophis pardalis on a Cuban stamp
There's much more to learn about tropidophiids, the Cuban radiation of Tropidophis in particular. To date, little ecological information has been collected on most species, owing in part to their rarity and in part to the difficulty of working in the region. How do five or six sympatric species partition resources and coexist in various parts of Cuba? What was the order of speciation and colonization of the islands, and when did it happen? Hopefully tropidophiids will be around long enough for us to find out. They are faced with numerous threats. As in many places, local people not especially fond of them, despite the fact that no Greater Antillean snakes are dangerous to people. Collection for the pet trade may also be a concern, particularly since one former government official in the Turks & Caicos Islands apparently granted a permit to reptile dealers to remove thousands of Tropidophis greenwayi from North Caicos for the pet trade, allegedly implying that it would be preferred if they removed all of the snakes! Throughout the West Indies, most native ecosystems have been absent for centuries, and increasingly rapid development, especially due to tourism, threatens what little remains. And introduction of non-native predators, particularly the Small Indian Mongoose (Herpestes javanicus), may be their biggest threat. As early as 1919, herpetologist Thomas Barbour wrote "In Jamaica [Tropidophis maculatus] is almost extinct owing to the appetite of the introduced mongoose". Ironically, Operation Mongoose was the codename for the Kennedy administration's attempt to create Cuban diplomatic, political, and economic isolation in hopes of weakening Castro’s regime. Cats, dogs, rats, goats, pigs, cane toads, and even other introduced snakes also threaten not just tropidophiids, but all 120+ snake species endemic to the West Indies as well as the rest of the native fauna. Improved PR and conservation programs have benefited several lizard species, and could help snakes too.

Tropidophis haetianus
I'm going to go ahead and wager that we'll discover a few new species of Tropidophis in the not-too-distant future, and that possibly the mainland species will get moved into a new genus. I also think that we need a more creative common name for them than "dwarf boa", preferably one that doesn't include the word "boa" at all. One existing option is "wood snakes", which is mediocre at best. They are also called "rock pythons" in the Caicos Islands, an equally misleading name as "dwarf boa", "culebras bobas" (dumb snakes) in Cuba, and "shame snakes" on Andros Island in the Bahamas, both of which may refer to their head-hiding defensive behavior. However, my favorite is the name they are known by in many parts of the West Indies: "thunder-snakes", because they are more frequently seen after severe rainstorms. Caribbean Thunder-snakes has a nice ring to it, and it could help improve their image.

1 1: Constriction behavior has become a lot more variable within the Colubroidea, where it has also been lost in several venomous lineages. Venom and constriction can be thought of as two different solutions to the same problem—how to kill large prey without exposing yourself to undue risk. Also, the contention that constriction and large gape size were lost in fossorial henophidians (aka "regressed" macrostomatans, including uropeltids, anomochilids, and aniliids) is seemingly contradicted by the complex multipinnate morphology of their jaw adductor muscles, which is sufficiently similar to that of their lizard ancestors that it is unlikely to have re-evolved in the exact same way multiple times. This problem might also be an issue for scolecophidians, given that they have similar jaw muscle morphology to pipesnakes but appear to be more closely related to other living snakes than they are to some basal fossil macrostomate snakes with limbs (symoliophiids). Stay tuned for more on the unresolved relationships at the base of the snake family tree, including a look at what fossil snakes can tell us.

2 2: All four genera (Exiliboa, Ungaliophis, Tropidophis, and Trachyboa) either completely lack a left lung or have a greatly reduced one, a characteristic they share with anomochilids and some caenophidians, but not with most other henophidians, which have a somewhat reduced but functional left lung. In addition, all four genera also have a "lung" on the dorsal wall of the trachea: the tracheal cartilages do not form closed rings but remain open on the top, where a greatly expanded ligament forms the tracheal lung. It has alveoli just like a regular lung, which are especially deep near the head, and is contiguous with the true lung in the vicinity of the heart. But, although this might seem like very strong evidence that these four genera are closely related, tracheal lungs of diverse structure are widespread among snakes, being found in certain scolecophidians, xenophidiids, acrochordids, vipers, atractaspidids, sea snakes, and many colubroid snakes.

3 3: A tantalizing bit of evidence emerged in 2008—biologists in Brazil videotaped the prey subjugation behavior of a captive Anilius scytale, which essentially constricted an amphisbaenian that they tried to feed it. In general its constriction behavior agreed with that of other henophidia, although it was more variable in the particulars, which could have been due to the difficulty of holding onto the elongate, "vigorous and constantly twisting prey". But, data from a single observation do not a generalization make, and more studies are needed.

4 4: Fossils of t
en extinct species in five genera from the Paleocene, Eocene, and Oligocene of Europe, Africa, & North and South America have been assigned to the Tropidophiidae, although all of them are probably actually either ungaliophiines or stem afrophidians. Two genera, Falseryx and Rottophis, both from the Oligocene of western Europe, have some similarities with living tropidophiids as well as with ungaliophiines, but for the most part their skulls are poorly preserved, leaving paleontologists to work on just their vertebrae. Paleogene erycines dominated the snake fauna of North America prior to the Miocene explosion of colubroids, but as far as we know all of these species were much more closely related to modern rosy and rubber boas than they were to tropidophiids. The only unequivocal tropidophiid fossils are from the Pleistocene of Florida and the Bahamas.


Thanks to Kenny Wray, Nick Garbutt, Alex Figueroa, Patrick Campbell, Pedro Bernardo, and Carlos De Soto Molinari for the use of their photographs.


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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.