Monday, May 25, 2015

Linnaean Snakes: Part I

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

Although recent findings have shed new light on the (so far) oldest-known fossil snakes, extending the fossil record of snakes back in time an incredible 70 million years, this article is about a more anthropocentric definition of "the first snakes". It's about the first snakes to be named and described using the modern system of classification: those described and classified by Linnaeus in the 10th edition of his Systema Naturae, using consistently together for the first time a binomial naming system for genera and species and a hierarchical category system for higher taxa (i.e., families, orders, classes, phyla, and kingdoms). Although Darwin's theory of evolution has ultimately refocused modern taxonomy on cladistics and phylogenetic trees, the Linnaean system is not wholly incompatible with our new understanding of the common ancestry of all life, and has and will continue to be used.

Carl Linnaeus (left) and Peter Artedi (right)
Carl Linnaeus was primarily a botanist, coining Latin names for and describing over 7,700 species of plants in his lifetime. However, he did a pretty good job of naming and describing species of animals as well, with over 4,400 to his name. His interest in describing animals derived partly from an agreement he made with his friend and one-time rival, Peter Artedi, when the two men were students: that if either of them should die, the other would complete their life's work. Artedi, an ichthyologist, drowned at age 30 (wrote Linnaeus, "too early...did the most distinguished of ichthyologists perish in the waters, having devoted his life to the discovery of their inhabitants!"), so Linnaeus took it upon himself to organize, complete, and publish Artedi's work on the classification of fishes. In truth, the two men developed the basics of zoological nomenclature together, and if Artedi had lived he probably would have shared equally in the renown which has come to Linnaeus today.

Tantilla melanocephala from the King of Sweden's collection
The snakes that Linnaeus described came primarily from a few sources. Several small collections ('curiosity cabinets') made by European aristocrats and businessmen formed the basis of a handful of his zoological dissertations, short papers written primarily by Linnaeus and defended by his students at the University of Uppsala, as was the custom at the time. One such dissertation, Amphibia Gyllenborgiana (defended by B. R. Hast in 1745), describes a collection donated by the university chancellor, Count Carl Gyllenborg, which contained the first attempt to classify snakes according to their numbers of scales, rather than their colors or patterns. Another, Surinamensa Grilliana (defended by Peter Sundius in 1748), describes a collection acquired with the help of Claes Grill, a wealthy merchant with an interest in natural history who used his directorship of the Swedish East India Company to obtain plants and animals from Surinam. Some of these specimens are still in the museum in Uppsala, including a caecilian, two Red Pipesnakes, a false coralsnake, and a parrotsnake. These dissertations do not use the binomial nomenclature for which Linnaeus is now famous. A few years later, Linnaeus was asked by the King and Queen of Sweden to organize, describe, and publish accounts of their personal natural history collections. In those days, it was as fashionable to collect objects of natural history, such as shells, insects, and preserved specimens, as it is to collect art today. The king in particular had amassed a large collection of snakes, many of which are still in the Swedish Museum of Natural History today (and looking remarkably well for being almost 300 years old), and these are described in Linnaeus's 1754 Museum Adolphi Friderici. During the 1750s and 60s, many of Linnaeus's students (which he called his "apostles") traveled the world collecting and sending him specimens, but in accordance with his interests they mostly sent him plants. A few students, including Pehr Kalm, who explored and collected in North America, and Fredrik Hasselqvist, who explored the Middle East, sent Linnaeus a few reptiles. Almost half of the snakes in Systema Naturae are from the king's collection, and most of the others are from the collections and works of two Dutch naturalists whose collections Linnaeus had seen as a young traveler: Albertus Seba, who wrote a Thesaurus of animals with many engravings (including hundreds of snakes), and Laurens Theodorus Gronovius, who worked mostly on fish (the distinction between fish and reptiles was still a bit hazy at the time). Although Linnaeus no doubt could have read about other snakes, he was skeptical of anything he had not examined himself1, and limited his published descriptions to specimens he could examine personally.

Title page of the 10th edition
In the 10th edition of his Systema Naturae, Linnaeus listed a total of 110 species in the order Serpentes, in six genera: Crotalus, Boa, Coluber, Anguis, Amphisbaena, and Caecilia. The first three will be familiar to any snake enthusiast, but the latter three, while legless, have since been reclassified as lizards or amphibians2. Of the 100 species that are actually snakes, 74 are still considered valid today. Linnaeus added 18 more snake species in his 1766 12th edition3, 13 of which are still valid, for a grand total of 87 snake species currently bearing his name, over 2% of modern species; only the authors of Erpétologie Générale can claim more. For reptiles as a whole he still ranks as the 9th most prolific taxonomist4. Pretty good for a botanist. To be fair, Linnaeus had the distinct advantage of Systema Naturae's 10th edition being later declared the starting point of zoological nomenclature, so he has benefited from having any names which preceded his automatically invalidated, whatever their notoriety. His cavalier attitude towards the work of those who came before him rankled many of his contemporaries, although he cited their descriptions wherever he could verify them. This also means that it was technically impossible for him to have "redescribed" any taxa, as many later authors often did, even though in reality of course many kinds of snakes were already recognized and some had names dating back to antiquity (many of which he used). Only 14 of the 100 snake species in SN10 were described therein for the first time. All these advantages didn't stop him from naming invalid species though—26 of the 100 species in the 10th edition (and 5 in the 12th) he described twice, under two different names; that is, later herpetologists decided that the specimens in his descriptions were members of the same species and synonymized (or "lumped") them, which accounts for the reduction in his total number of snake species from 118 to 87.

The travels of Linnaeus's students (click for larger version)
Linnaeus worked on classifying many different groups of organisms, and he always worked in great haste, because there was so much to do. As a result, he could be fairly careless, particularly when it came to the geography of his specimens (i.e., his type localities). Because he had not actually been to many of the places where his specimens came from, he had to rely on the word of others for this information. When specimens came from his apostles or from other contemporaries, they usually had pretty accurate, if general, locations (e.g., 'America', 'Africa'). If they were older, such as those in the collections of Gronovius, Seba, and the king, they were often accompanied by unverifiable locations, many of which were incorrect. In fact, only 33 of the 74 snake species in Linnaeus's SNX have unambiguously correct location information. A further 21 are unambiguously wrong, and 20 bear the label 'Indiis', which might refer either to India or to the West Indies (and, in either case, is still incorrect for certain specimens). In certain cases, it almost seems that labels were switched, such as a South American Xenodon from 'Asia' and an Asian Amphiesma from 'America'. Overall his snakes are fairly diverse, with good geographic representation, except for Australia, which was first botanized in 1770, close to Linnaeus's death, by Linnaean apostle Daniel Solander, sailing onboard James Cook's Endeavour along with Joseph Banks (and resulting in the name of Botany Bay).

Many other later taxonomists reorganized Linnaeus's snake genera, breaking up his combinations by placing the vast majority of the snakes Linnaeus described into new genera. However, 4 of his snake species retain their original genus and species names today. That three of them would was inevitable because of the principle of priority and the "type" concept5, but the fourth is a bit of a bonus. Next month, in Part II, we'll take a closer look at these four species, named by Linnaeus when George Washington was in his twenties, 257 years ago.

1 Seba's Thesaurus contained a now-famous image of a hydra, which Linnaeus inspected in Hamburg in 1735 and exposed as a hoax made from weasels and snake skins. This and other mythical creatures he listed as "animalia paradoxa" in early editions of Systema Naturae, although some (like the paradoxical frog) turned out to be real! For instance, he was correct in stating that "All the other dragons listed by authors are fictitious, like the hydra, which I saw at Hamburg, but which was an outstanding work, not of nature, but of art.", but erred in thinking that "The horned viper is a coluber fabricated by the craft of the Arabs, who pierced its head with the claws of a small bird and then inserted them there".

2 Originally, two scolecophidians (Amerotyphlops reticulatus and Typhlops lumbricalis), the monotypic Anilius scytale, a pipesnake (Cylindrophis maculatus), and two sand boas (Eryx colubrinus and E. jaculus) were placed in Linnaeus's genus Anguis, but were later reclassified (correctly) as snakes.

3 Nothing new was added to the 11th edition, which was simply a reprint of the 10th. In 1789, 13 years after Linnaeus's death, Johann Friedrich Gmelin added three more species of snakes to the 13th and last edition, by which time other zoologists such as Laurenti (who also split reptiles from amphibians and tripled the number of reptile genera) had already contributed a great deal to snake taxonomy.

4 It's fair to say that Linnaeus didn't like snakes or other reptiles. In the first edition of Systema Naturae he wrote: "The Creator in his benignity has not wanted to continue any further the Class of Amphibia for, if it should enjoy itself in as many Genera as the other Classes of Animals, or if those things were true that the Tetralogists have fabricated about Dragons, Basilisks, and such monsters, the human genus would hardly be able to inhabit the earth." He continues in Museum Adolphi Friderici: "Truly formidable are the arms which the Lord of nature has given to some animals. Though he has left serpents destitute of feet, wings, and fins, like naked fishes, and has ordered them to crawl on the ground exposed to all kinds of injuries, yet he has armed them with dreadful envenomed weapons: but, that they may not do immoderate mischief, he has only given these arms to about a tenth part of the various species; at the same time arraying them in such habits that they are not easily distinguishable from one another, as the rest of animals are; so that men and other creatures, while they cannot well distinguish the noxious ones from those which are innocent, shun them all with equal care. We shudder with horror when we think of these cruel weapons. Whoever is wounded by the Hooded Serpent (Coluber Naja) expires in a few minutes; nor can he escape with life who is bitten by the Rattle-snake (Crotalus horridus) in any part near a great vein. But the merciful God has distinguished these pests by peculiar signs, and has created them most inveterate enemies; for as he has appointed cats to destroy mice, so has he provided the Ichneumon [mongoose] (Viverra Ichneumon) against the former serpent, and the Hog to persecute the latter. He has moreover given the Crotalus a very slow motion, and has annexed a kind of rattle to its tail, by the motion of which it gives notice of its approach...On account of these and various other poisonous serpents and worms of India, which crawl upon the ground, swim in the waters, or twine among the branches of trees, we prefer our barren and craggy woods to the everblooming meadows and fruitful groves of Indian climes; and we had rather suffer the inconveniences of our northern snows, than enjoy their enviable luxuries."

5 The principle of priority states that the first name given to a plant or animal is the correct one, and all subsequent uses of other names for that species or of that name for other species are invalid. Some formal exceptions are allowed on a case-by-case basis. The type concept permanently associates a species with a genus, which helps biologists decide which genus name to use for which species when genera are split or lumped.


Thanks to my mom for getting me William Blunt's Linnaeus for Christmas this year, which inspired this article.


Andersson, L.G. 1899. Catalogue of the Linnaean type-specimens of snakes in The Royal Museum in Stockholm. Bihang till Kongl. Svenska Vetenskaps-Akademiens Handlingar 24:1-35 <link>

Blunt, W. 2002. Linnaeus: The Compleat Naturalist. Princeton University Press, Princeton, New Jersey, USA <link>

Gronovius, L.T. 1756. Museum Ichthyologicum. Theodorum Haak, Lugduni-Batavorum <link>

Linnaeus, C. 1745. Amphibia Gyllenborgiana. Uppsala University, Uppsala. Dissertation (B. R. Hast, respondent)

Linnaeus, C. 1748. Surinamensia Grilliana. Uppsala University, Uppsala. Dissertation (P. Sundius, respondent) <link>

Linnaeus, C. 1758. Systema naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata. Stockholm. <link>

Linnaeus, C. 1764. Museum S. R. M. Adolphi Friderici. Stockholm <link/translated>

Linnaeus, C. 1766. Systema naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio duodecima, reformata. Stockholm <link>

Kitchell, K. and H.A. Dundee. 1994. A trilogy on the herpetology of Linnaeus's Systema Naturae X. Smithsonian Herpetological Information Service 100 <link>

Seba, A. 1734-1765. Locupletissimi rerum naturalium thesauri accurata descriptio, et iconibus artificiosissimis expressio, per universam physices historiam :opus, cui, in hoc rerum genere, nullum par exstitit. Apud Janssonio-Waesbergios & J. Wetstenium & Gul. Smith, Amstelaedami <link>

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

Tuesday, April 21, 2015

Spitting cobras

This post will soon be available in Spanish!

Spitting cobras have been known for centuries,
as you can see from this report published in the
Journal of the Bombay Natural History Society in 19001

A clever comic from birdandmoon
highlighting the fact that king cobras
are not true cobras
Cobras are some of the most iconic snakes in the world, instantly recognizable by their hoods even to those who have never seen one. They are also among the most dangerous snakes—fast-moving, with potent neurotoxic venom, cobra bites cause injury or death to many people in Asia and Africa. Cobras are elapids, together with coralsnakes, mambas, kraits, seasnakes, and numerous terrestrial Australian snakes both well-known and obscure. What unites these ~350 species of snakes is their short, immovable, and hollow ("proteroglyphous") fangs. Elapids probably evolved in Asia between 25 and 30 million years ago. By 16 million years ago, cobras were found in Europe, where they no longer live, and in Asia and Africa, where they are still found today. The core cobra clade consists of three small genera (Hemachatus, Aspidelaps, and Walterinnesia) and one large one, Naja. Other hooded snakes that are usually called "cobras" include tree cobras (genus Pseudohaje), whose placement remains uncertain, and the king cobra (Ophiophagus hannah), which is probably more closely related to mambas than it is to true cobras. Ironically, most people, if asked for a species of cobra, would almost certainly come up with the king first. But, probably they would think of a spitting cobra second, and with good reason from an evolutionary perspective, as we shall see.

Mozambique Spitting Cobra (Naja mossambica)
Almost all spitting cobras belong to the genus Naja, a large genus that comes from the Sanskrit word for snake, nāga. Literature buffs will recognize the name of the cobras in Kipling's Rikki Tikki Tavi, which led to the name of the snake Nagini in the Harry Potter books. Over the past 50 years, the number of species within the genus Naja has risen from six to 292, and more will probably become recognized in the future. At least 15 of these species can spit their venom through the air. The best of them are capable of aiming at targets the size of a human face with >90% accuracy up to 8 feet away. This adaptation represents the only purely defensive use of venom by any snake. Vipers and other venomous snakes occasionally eject venom from their fangs into the air, particularly when being handled, but these snakes are not aiming at anything, so they are not really using their venom defensively. Spitting in cobras is an adaptation that involves changes to the morphology of the fangs, their head musculature, and the chemistry of their venom.

Fangs of  cobras progressively adapted for spitting.
Dotted lines show the venom canal, dark arrows indicate
the flow of water injected into the top of the fang.
Left: "normal" non-spitting cobra fang (Naja kaouthia)
Right: spitting cobra fang (Naja pallida)
The sutures are visible above the exit orifices.

From Young et al. 2004
All snake fangs are modified teeth provisioned with grooves that vary in depth and degree of closure. In vipers and elapids, the grooves are completely closed, forming hollow tubes, along the front edge of which a narrow suture can still be seen where the ridges forming the tube have come together in the developing embryo. In spitting cobras, the inside of this tube contains ridges, which act like rifling in a gun barrel to impart spin on the venom. The discharge orifice, located near but not at the point of the tooth (like a hypodermic needle), is large and elliptical in non-spitting cobras but small and round in spitting cobras, which has the same velocity-increasing effect as putting your thumb most of the way over the end of a garden hose. A sharp 90° bend at the distal end directs the jet of venom forward or slightly upward, instead of downward as in most snakes, and venom stream spins towards the exit orifice, which prevents the flow from slowing down as it goes through the sharp bend at the exit (similar strategies are used in pressure washers). These adaptations of the fang enable a cobra to spit venom in defense but do not prevent venom injection when biting, which is used both defensively and for killing prey. In fact, spitting cobras can meter the duration of their venom pulse, which is normally about five times longer during biting (1/4th of a second) than during spitting (1/20th of a second). This affects the quantity of venom ejected, which varies considerably from bite to bite and may consist of up to 100 times more venom than the fairly consistent 1.9-3.7 milligrams (~1/10th of a milliliter) of venom per spit. Most estimates suggest that a single cobra has enough venom to spit about 40-50 times consecutively. The fluid dynamics of such tiny volumes over relatively long distances are complex, and spitting cobra venom has shear-reducing properties, such as high surface tension and viscosity, which hold the droplets together as they fly through the air. Some species of spitting cobra eject their venom as a spray, whereas others eject two pressurized parallel streams. Reports of the maximum distance achievable by a spitting cobra vary from surely exaggerated distances of 12 feet or more to more believable (though still impressive) distances of five to eight feet.

Venom spray patterns of Red Spitting Cobras (Naja pallida)
From Westhoff et al. 2005
Middle: Examples of head movement patterns of  Black-necked
Spitting Cobras (Naja nigricollis). Black dots represent the
positions of the upper and lower jaws,  red dots indicate the
period of venom spitting.
From Westhoff et al. 2005
Bottom: Congruence between target (back; blue)
and cobra’s head (red; front plot) motion during spitting.
Data are offset 180 ms to reflect the cobra's reaction time.
From Westhoff et al 2010
Unlike vipers, cobras cannot move their fangs, so in order to accurately hit their targets, they move their heads instead. When a spitting cobra spits, it opens its mouth slightly and contracts the muscles around the venom glands so that a small amount of venom is forced out of the glands and down the venom canal of the fangs. At the same time, the upper lip scales and the fang sheaths are levered up out of the way and the maxilla levered down, removing soft tissue barriers between the venom glands and the fangs as well as between the exit orifices of the fangs and the air around them3. Most often, the spit is accompanied by slight movements of the head in response to change in direction of the target, which disperse the venom over an area about the size of a human face. Measurements indicate that more head rotation corresponds to a larger area covered by the venom stream, allowing cobras to adjust for target size and distance. Splattering of the venom when it hits the target and partial disintegration of the venom stream as it travels through the air increase the chance that at least some of the venom will hit the target's eye. Consequently, cobras only need to aim at the center of the face, rather than precisely at the eyes, in order to hit the eyes 90-100% of the time. They adjust for target movement by using a strategy familiar to any Space Invaders or Galaga player: firing not at where you are but at where you're going to beChameleonsarcher fish and spitting spiders do the same kind of thing. In some species venom spitting is often accompanied by an audible hiss as the cobra exhales, but in contrast to early reports that spitting cobras propelled their venom with their breath, this is not an essential part of the spitting process. In one experiment, spitting cobras restrained in tubes did not seem to suffer from reduced spitting ability or range. How do they choose their targets? Cobras have good vision and moving human faces are the stimuli that normally elicit spitting, although in lab experiments they will also spit at masks, photos of human faces, and even plain ovals without eyes, as long as they are moving, but not at moving triangles. Adult cobras will not spit at stationary human faces or moving human hands, although newly hatched cobras will spit at nearly anything, even if it is beyond their maximum target distance, including human hands, unhatched eggs, other baby cobras, and even their own reflection. Hatchling cobras also spit more of their venom, proportionally, and rotate their heads in a more pronounced fashion; their spitting performance improves following their first shed. Like many stereotypical snake defensive behaviors, most spitting cobras apparently habituate to humans when in captivity and are disinclined to spit after a while, although some spit without hesitation and willingness to express defensive behavior is very variable from individual to individual.

Sumatran Spitting Cobra (Naja sumatrana)
Although the color and consistency of spat venom does not change noticeably with repeated spitting, the venom chemistry of at least one species, Red Spitting Cobras (Naja pallida), changed over 10 minutes of repeated spitting. The quantity of venom remained the same and the toxin concentration rose over the first 20 spits, but both decreased afterward. The first five spits contained a protein that was not found in later spits, which might be involved in venom storage. Although this protein is non-toxic, most of the other molecules in spitting cobra venom are not. African spitting cobra venom is rich in cytotoxins and PLA2s, which cause tissue damage; spitting cobra cytotoxins lack certain acidic proteins, which frees them to damage tissues in the eyes. If even a small quantity of venom contacts the eye it causes instant, intense pain and damage to the cornea and mucous membranes. If left untreated, it can lead to blindness. Treating spitting cobra venom in your eyes involves flushing it out with water for 15-20 minutes. Anti-inflammatory eye drops are sometimes prescribed.

Rinkhals (Hemachatus haemachatus)
The 29 living species of Naja fall into four groups: a basal Asian clade of eleven species (subgenus Naja, including six accomplished spitting members, two non-spitters, and three species of intermediate spitting ability), an African spitting group of eight species (subgenus Afronaja), and two African non-spitting groups of six and four species, respectively (subgenus Uraeus, found mostly in open areas, and subgenus Boulengerina, found mostly in forests). This pattern of species relationships suggests that spitting evolved more than once! In Asia, the six spitting cobras (Naja siamensis, N. sumatrana, N. sputatrix, N. mandalayensis, N. samarensis, and N. philippinensis4) are probably one another's closest relatives, and their closest cousins are a group of three cobra species (Naja atra, N. kaouthia, and N. sagittifera) with somewhat modified fangs and intermediate spitting ability. They can spit their venom, but they do so rarely and with less accuracy than the "true" spitters. The remaining Asian cobras, Naja naja and Naja oxiana, do not spit their venom but nevertheless are more closely related to Asian spitting cobras than to other cobras. This means that venom spitting arose independently in the common ancestor of the seven species of African spitting cobras (N. pallida, N. nubiae, N. katiensis, N. nigricollis, N. ashei, N. mossambica, and N. nigricincta), which form a monophyletic group sometimes referred to as Afronaja. Their cousins, the other African Naja (i.e., subgenera Uraeus and Boulengerina), do not spit. Finally, a member of one of those small genera, a very interesting cobra known as the rinkhals (Hemachatus haemachatus) also spits its venom, indicating that venom spitting has evolved three times in cobras (or, alternatively, been lost twice, in Naja naja/N. oxiana and in the common ancestor of Uraeus and Boulengerina, with a third partial loss in N. atra & kin). Because the details of spitting behavior and morphology differ slightly among the three groups of spitting cobras, the former hypothesis is more likely.

The largest Giant Spitting Cobras (Naja ashei) can top 9 feet.
This species was described in 2007.
From Wüster & Broadley 2007
Why do some cobras spit their venom? Herpetologist Thomas Barbour, who published one of the first studies on spitting cobras, thought that spitting cobras evolved venom spitting for much the same reason that rattlesnakes were thought to have evolved their rattles—to alert large ungulates to their presence and avoid getting stepped on. He was speculating in the absence of any direct evidence when he wrote in 1922 that "The African veldt is the only other region in the world where snakes abound and where hoofed animals grazed in numbers comparable with those of the western American plains. Snakes probably found the heavy antelopes equally dangerous though unwitting foes and many antelopes probably suffered from snake bite. No rattle was evolved, however but some of the common veldt-ranging snakes secured protection in another way. Several common cobras and cobra-allies learned to expel their poison in a fine spray for very considerable distances, and with a fairly shrewd aim at the eye."

Nearly 100 years after Barbour, we have just as little direct evidence—published field observations of spitting cobras interacting with their non-human predators are non-existent. The main reason we now think that the evolutionary cause of these adaptations isn't so simple is that spitting is too old. Molecular dating methods suggest that African spitting cobras evolved about 15 million years ago, whereas the spread of open grasslands and their characteristic megafauna (elephants, etc.) didn't happen until about 5 million years ago. Asian spitting cobras don't inhabit open grasslands, so this hypothesis seems unlikely to explain their evolution either. African spitting cobras are eaten by birds and other snakes, against which spitting venom would be a relatively ineffective weapon, and in captive experiments cobras do not spit at mounted bird specimens. Given what we know about face targeting, it's possible that spitting may represent a defense that is specifically adapted for use against primates [Edit: Harry Greene hinted at this idea in his recent book, Tracks and Shadows]. Barbour's comment that "...[venom spitting] must antedate man's coming, for contact between man and the snakes can hardly be conceived as sufficiently frequent to account for the modification" may be technically correct, but the evolution of spitting cobras coincides roughly with the evolution of apes in Asia and Africa, which (as we all know) are diurnal primates with forward-facing eyes, some of which are omnivorous and many of which (ourselves included) habitually kill snakes either for food or in defense. Could it be that spitting cobras evolved their venom spitting capacity to deal with threats from our own ancestors? Only further research into the co-evolution of apes and snakes can tell us. Perhaps this is why, although certain toads, salamanders, insects, and scorpions can also eject their toxin defensively, spitting cobras are by far the longest- and best-known organisms to do so. Clearly, much remains to learn about them and their fascinating habits.

1 The cobra in this account was undoubtedly Naja mandalayensis, which was described by Joe Slowinski & Wolfgang W
üster 100 years later. Before 2000, no spitting cobras were known from Burma. Cobra specimens with fangs highly modified for spitting from northeastern India may represent a seventh species of undescribed Asian spitting cobra.

2 This number includes species of cobras formerly placed in the genera Boulengerina and Paranaja, both of which have been synonymized with Naja in the last 15 years. In part, the reason for this change is that, when scientists realized that some species of Naja were more closely related to Boulengerina and Paranaja than they were to other Naja (i.e., that Naja was paraphyletic), they were reluctant to split up the genus Naja because they didn't want to change the name of medically-important snakes and create potential confusion. However, a few sources use Afronaja and other other subgenera as full genera anyway.

3 The fang sheath is soft tissue that completely surrounds the fang at rest, including at the top, which keeps the venom from dribbling out. In other venomous snakes, physical contact with a target is required for displacement of the fang sheath and release of venom, but spitting cobras have co-opted the movements normally used for jaw-walking over a prey item (the ‘pterygoid walk’) to free their fangs for spitting in the absence of any external physical contact. This has been termed the "buccal buckle" (pronounced "buckle buckle") by the research group of Bruce Young, of Kirksville College, which has studied several aspects of the functional morphology of spitting in cobras.

4 Naja philippinensis is 
the only spitting cobra species with pronounced sexual dimorphism in discharge orifice size—females have longer orifices less well-adapted for spitting, whereas males have small round orifices. The evolutionary causes and consequences of this dimorphism are not understood.

This post is part of a Reptile and Amphibian Blogging Network (RAmBlN) online event called #CrawliesConverge. We are writing about convergent evolution in reptiles and amphibians. Find our event schedule here, or follow on Twitter or Facebook.


Thanks to Dan Rosenberg, Stu Porter, and Ray Hamilton for allowing me to use their photos.


Barbour, T. 1922. Rattlesnakes and spitting snakes. Copeia 105:36-38 <link>

Berthé, R., S. de Pury, H. Bleckmann, and G. Westhoff. 2009. Spitting cobras adjust their venom distribution to target distance. Journal of Comparative Physiology A 195:753–757 <link>

Berthé, R.A., G. Westhoff, and H. Bleckmann. 2013. Potential targets aimed at by spitting cobras when deterring predators from attacking. Journal of Comparative Physiology A 199:335-340 <link>

Bogert, C.M. 1943. Dentitional phenomena in cobras and other elapids, with notes on adaptive modifications of fangs. Bulletin of the American Museum of Natural History 81:285-360 <link>

Cascardi, J., B.A. Young, H.D. Husic, and J. Sherma. 1999. Protein variation in the venom spat by the red spitting cobra, Naja pallida (Reptilia: Serpentes). Toxicon 37:1271-1279 <link>

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

Monday, March 16, 2015

Rattlesnake Roundups

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.


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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.