|Rough Green Snakes (Opheodrys aestivus)|
mostly eat insects and spiders.
Photo by Kevin Durso
Tuesday, December 3, 2013
Wednesday, November 27, 2013
|Map of snake envenomings per year, from Wikimedia Commons|
|Copperheads (Agkistrodon contortrix) bite|
a few hundred people a year in my home state of
North Carolina, more than in any other state.
Fatalities are exceedingly uncommon.
|Western Diamondback Rattlesnakes (Crotalus atrox)|
are large and widespread in the southwestern USA.
A recent study showed rattlesnake size to be among the
most important factors determining bite severity, with the
largest snakes causing the most serious bites.
|Figure from Gibbons & Dorcas (2002)|
|Black Mambas (Dendroaspis polylepis) are among|
Africa's most dangerous snakes, but they still kill fewer
people than hippos or mosquitos
|CroFab antivenom used to|
treat most snakebites in the USA
Yet more than 1 in 20 people in the USA have a pathological fear of snakes, as defined by criteria including uncontrollable, greater than justified, and significantly interferes with a person’s routine, occupational or academic functioning, or social activities or relationships. Leading to situations like this recent news story and this bizarre interaction between a man, a gun, and a snake. Risk perception is influenced by many things, including the rarity of the event, how much control people think they have, the adverseness of the outcomes, and whether the risk is voluntarily or not. For example, people in the United States underestimate the risks associated with having a handgun at home by 100-fold, and overestimate the risks of living close to a nuclear reactor by 10-fold. Ironically, evidence suggests that two of these things (how much control you have and how voluntary the risk is) are actually quite high for snakebite, despite popular perception that is it low.
fady to kill any snake. In contrast, in Australia people seem to have a relatively high level of respect for snakes and don't seem to mess with them solely out of machismo the way they do in the USA. Venomous snakebites are relatively rare, which is remarkable considering that the majority of snakes in Australia are venomous. I heard a story recently about a newly-hired Australian CEO of an American mining company. When the new boss asked about the snake policy, the employees jokingly replied that it was "a No. 2 shovel". The Australian CEO was not amused, because at his previous company Down Under routinely relocated much more dangerous snakes at their job sites. He instituted a company-wide training program to teach safe venomous snake practices. These classes are also available to the general public in some areas, especially in southern Africa.
1 Venomous snakes that are striking at their prey practically always inject venom, and in fact can precisely meter their venom so that they inject exactly the right amount needed to kill each particular prey item, based on its mass. Fortunately for humans, there are no venomous snakes large enough to consider us prey.↩
2 Although global snakebite statistics frequently list 0 fatalities out of 200-300 snakebites for Canada, this seems not to be quite accurate. In Ontario, at least two people have been killed by Timber Rattlesnakes (Crotalus horridus), a soldier who was bitten at the battle of Lundy's Lane near Niagara Falls in 1814, and an American Indian chief prior to 1850. Two or three people have been killed by bites from Massasaugas (Sistrurus catenatus) in Ontario, all before 1962, and between 0 and 10 people were bitten annually from 1971-2007, mostly men aged 10-29. In 1981, a man who was "quite intoxicated" was killed by a bite from a Northern Pacific Rattlesnake (Crotalus oreganus) on the Nk’meep reserve near the town of Osoyoos in British Columbia's Okanagan Valley. He was the first person to be bitten by a native venomous snake in BC in over 50 years. The only other Canadian provinces that are home to venomous snakes are the Prairie Provinces of Alberta and Saskatchewan, where no recorded deaths have occurred from Prairie Rattlesnake (Crotalus viridis) bites. So we can conclude that native snakebites in modern Canada are even more infrequent than but follow the same basic pattern as those in the USA.↩
3 In the US, relative to dying from heart disease (1 in 5), cancer (1 in 7), in a motor vehicle accident (1 in 80), in a fall (1 in 185), from a gunshot (1 in 300), by drowning (1 in 1100), by choking (1 in 4400), from drinking too much alcohol (1 in 10,900), by a sting from a wasp, bee, or hornet (1 in 63,000), from being struck by lightning (1 in 80,000), from a dog bite (1 in 120,000), or in an earthquake (1 in 150,000), you are very unlikely to be killed by a snake (1 in 480,000). The only less-likely causes of death are being trapped in a low-oxygen environment (1 in 548,000), being killed by ignition or melting of nightwear (1 in 767,000), and being bitten by a spider (1 in 960,000). These odds are for your entire lifetime; your annual chance of being killed by a venomous snake is more like 1 in 50 million. Worldwide, they're more like 1 in 200,000, which is a lot higher but still pretty low overall.↩
(click here for a full list of references pertaining to snakebite)
Gibbons, J. W. and M. E. Dorcas. 2002. Defensive behavior of Cottonmouths (Agkistrodon piscivorus) toward humans. Copeia 2002:195-198 <link>
Glaudas, X., T. M. Farrell, and P. G. May. 2005. The defensive behavior of free–ranging pygmy rattlesnakes (Sistrurus miliarius). Copeia 2005:196-200 <link>
Janes Jr, D. N., S. P. Bush, and G. R. Kolluru. 2010. Large snake size suggests increased snakebite severity in patients bitten by rattlesnakes in southern California. Wilderness and Environmental Medicine 21:120-126 <link>
Juckett, G. and J. G. Hancox. 2002. Venomous snakebites in the United States: management review and update. America Family Physician 65:1367-1375 <link>
Parrish, H. M. 1966. Incidence of treated snakebites in the United States. Public Health Reports 81:269-276 <link>
Swaroop, S. and B. Grab. 1954. Snakebite Mortality in the World. Bulletin of the World Health Organization 10:35-76 <link>
Tierney, K. J. and M. K. Connolly. 2013. A review of the evidence for a biological basis for snake fears in humans. The Psychological Record 63:919-928 <link>
Walker, J. P. and R. L. Morrison. 2011. Current management of copperhead snakebite. Journal of the American College of Surgeons 212:470-474 <link>
Friday, November 1, 2013
Normally when someone asks me how to tell the difference between a snake and a legless lizard, I tell them to look at the eyes. Lizards have eyelids whereas snakes do not. Whenever I say this I am lying, although really I am just oversimplifying for the sake of clarity. Most lizards have obvious movable eyelids and so can blink like we do. Snakes, by contrast, seem not to have eyelids. They are ever-staring, ever-vigilant. Ben Franklin esteemed the rattlesnake as a symbol of vigilance because its eyes were always open.
|Eye of an Eastern Ribbonsnake (Thamnophis sauritus)|
during the phase prior to shedding when fluid
has built up between the old and new spectacles
|The horizontal, key-shaped pupil|
of Ahaetulla prasina
Until recently, no one had considered whether movement of blood into and out of the spectacle blood vessels might aid snakes in being able to see. In an article published this week in The Journal of Experimental Biology, Kevin van Doorn and Jacob Sivak of the University of Waterloo in Ontario presented the first evidence that snakes are able to do this. When van Doorn was investigating the mechanisms snakes' eyes use to focus, he noticed the blood vessels in the spectacle, which led him to look more closely at their function. He found that coachwhips, another highly visual species, were able to reduce blood flow to the spectacle in the presence of a potential threat. At rest and undisturbed, newly oxygenated blood flowed into the spectacle blood vessels of the coachwhips for about a minute at a time, interspersed with approximately two minute periods during which no flow took place. When an experimenter walked into the room to perform some routine tasks, spectacle blood flow was almost completely cut off. What little flow there was during this period occurred in short spurts of around 30 seconds each, about half the length of the flow period in undisturbed coachwhips. When the experimenter left the room, the pattern of blood flow in the snakes' eyes returned to normal almost immediately.
|Shed skin of a Cornsnake (Pantherophis guttatus)|
showing the shed spectacles
Geckos and some other lizards also have spectacles. A few other species of tetrapods have blood vessels in their optical path, including manatees, armadillos, and some blind salamanders, none of which are renowned for their visual prowess. Little is known about the images these vessels might project onto the vision of these animals, but because they are part of the cornea and so move about with the eye rather than remain stationary relative to it, their area of occlusion would appear to remain stationary to the animal. This is not true for animals with nictitating membranes (diving animals such as penguins or crocodilians) or those with spectacles, both of which have the potential to interrupt the animal's vision. We don't know yet how crocodilians and geckos deal with this issue, but as with so many other features of their lives, snakes have evolved an ingenious and potentially unique solution to a vexing problem, allowing them to remain vigilant as well as keep their eyes protected. Snakes have guarded the Golden Fleece in the Greek tale of the hero Jason and his band of Argonauts, a treasure chamber beneath an ancient city in Rudyard Kipling’s The Jungle Book, and various other treasures in Hindu, Inca, and Basque mythology, all with their eyes closed.
Correction: I originally said that the fovea work was done on Ahaetulla prasina, but it was actually Ahaetulla nasuta. Both species have horizontal pupils so it is likely that the reduction in blood vessels is found in both.
Baker, RA, TJ Gawne, MS Loop, and S Pullman (2007) Visual acuity of the midland banded water snake estimated from evoked telencephalic potentials. J. Comp. Physiol. A 193, 865-870 <link>
Crump, ML (in press) Amphibians, Reptiles, and Humans: Cultural Perceptions and Conservation Consequences. University of Chicago Press.
Foureaux, G, MI Egami, C Jared, MM Antoniazzi, RC Gutierre, and RL Smith. (2010) Rudimentary eyes of squamate fossorial reptiles (Amphisbaenia and Serpentes). Anat. Rec. (Hoboken) 293, 351-357 <link>
Franklin, B (1775) The rattlesnake as a symbol of America. Pennsylvania Journal. <link>
Lüdicke M, 1969. Die kapillarnetze der brille, der iris, des glaskörpers und der chorioidea des auges vom baumschnüffler Ahaetulla nasuta Lacepede 1789 (Serpentes, Colubridae). Zoomorphology 64:373-390.
Mead, AW (1976) Vascularity in the reptilian spectacle. Invest. Opthalmol. Vis. Sci.15, 587-591 <link>
Neher, EM (1935) The origin of the brille in Crotalus confluentus lutosus (Great Basin rattlesnake). Trans. Am. Ophthalmol. Soc. 33, 533-545 <link>
Quekett, J. (1852). Observations on the vascularity of the capsule of the crystalline lens, especially that of certain reptilia. Trans. Microsc. Soc. Lond. 3, 9-13. doi:10.1111/j.1365-2818.1852.tb06020.x
van Doorn, K. and Sivak, J. G. (2013). Blood flow dynamics in the snake spectacle. J. Exp. Biol. 216, 4190-4195 <link>
Tuesday, October 15, 2013
|Brown Anole (Anolis sagrei)|
The purpose of my trip
|Map of visits to this blog|
|The first photo|
We found this [snake shed] in our barn near Lawrence Kansas. I had this extreme fear of snakes so I became proficient in identifying them, if I see them. We have only seen 3 types of venomous snakes in our area, the timber rattler, the western massasauga, and the osage copperhead. Unfortunately, I find that I am truly inept at identifying them by their skins.
We have seen more poisonous snakes this year than usual and we found this skin inside our barn. It very easily could have been trapped inside as we close it up every other evening. We primarily use the barn for storage and workshop. Hopefully, we have allowed plenty of opportunity for the snake to escape.
I mainly want to know if you can help me to identify whether this is a poisonous snake. After reading your blog I am concerned is that it is possibly a copperhead and that it could be hiding. There are numerous places for a creature to stay hidden in our 70 ft barn and I fear that I will open a bin or cabinet and find it, dead or alive.
We love our wildlife and try to be protective and careful, but it seems we have failed at this lately as we recently had to scare an endangered skink out of the barn.
I would appreciate your assistance in possibly identifying this snake. I don't think we have the tail end of the skin. We do have the fairly intact head portion of the skin and can send more pics if needed.
Your blog is very informative and I learned a great deal from it. I thank you in advance for your assistance.
|The second photo, |
showing divided subcaudals
It is still scary that we didn't see it! We live in a rural area very near to public hunting and fishing but don't have a lot of traffic. It makes my blood boil at the number of snakes we see dead on the SIDES of the roads!
Please keep up the great work! Yours was the first site when I googled snake skin id and by far the most informative i found! I learned so much by reading your blog and I really feel that people need more education about snakes!
- Basics of snakebite
- Venomous bites from "non-venomous" snakes
- Common urban snakes
- Snake predators
- Invasive snakes
- Some personal stories about how I became interested in herpetology
- Several taxon-specific posts
|Cornsnake from the island|
|Me with Diamondback|
Wednesday, September 25, 2013
|Solenoglyphous fangs of a Gaboon Viper|
|Cross-sections of fangs:|
F is an aglyphous tooth.
G is an opisthoglyphous fang.
H is a proteroglyphous fang.
I is a hollow solenoglyphous fang.
From Bauchot (2006)
|Folding of solenoglyphous fangs.|
Fang is in red, maxilla green,
prefrontal orange, pterygoid yellow,
ectopterygoid purple. Vipers lack
premaxillary and palatine teeth.
From Bauchot (2006)
|Modified solenoglyphous fang of|
African Burrowing Asp (Atractaspis engaddensis)
|Proteroglyphous fangs of an Eastern Green Mamba|
(Dendroaspis angusticeps). Don't try this.
From Bauchot (2006)
|Opisthoglyphous fang of Eastern Hog-nosed Snake|
|Opisthoglyphous fangs of Boomslang (Dispholidus typus)|
Don't do this either.
|A: python, B: viper, C: rear-fanged colubroid, D: cobra|
The f marks the portion of the maxilla where the fang develops.
E shows the elongation of the posterior part of the
maxilla pushing forward the developing fang of a
night adder (d.a.o. = days after oviposition)
From Vonk et al. 2008
|Relative size of the venom gland (VG) in|
A: rear-fanged colubrid (Helicops leopardinus),
B: boomslang, C: homalopsid,
D: cornsnake, E: African egg-eater
SG = supralabial salivary gland
From Fry et al. 2008
|Both boas and pythons have only|
aglyphous teeth, which is about
the only thing this film got right.
There are very few dangerous species of aglyphs, but one, Rhabdophis tigrinus, is becoming well-known as one of the only snakes capable of sequestering toxins from its prey for use in its own defense. This species has enlarged posterior maxillary teeth that lack grooves, so they are by definition aglyphous. However, it has relatively potent venom and has caused the deaths of several people. Among colubroids, the distinction between opisthoglyphs and aglyphs has never been entirely clear, but I'm distinguishing between them here because they are two of the four traditionally recognized types of snake teeth. Although the four types of snake teeth in this article are commonly discussed, a more accurate classification for snake teeth might be to divide them into tubular (the fangs of viperids, elapids, and atractaspidines), grooved (the rear fangs of non-front-fanged colubroids), and ungrooved (all other snake teeth).
|Aglyphous (ungrooved) teeth and rear fangs of|
From Mittleman & Goris 1974
Bauchot R, editor. 2006. Snakes: A Natural History. New York, New York: Sterling Publishers. <link>
Cundall, D., (2002) Envenomation strategies, head form, and feeding ecology in vipers. In: Biology of the Vipers: 149-162. G. W. Schuett, M. Höggren, M. E. Douglas & H. W. Greene (Eds.). Eagle Mountain Publishers, Eagle Mountain, UT <link>
Greene, H. W. (1997) Snakes: The Evolution of Mystery in Nature. Berkeley: University of California Press <link>
Fry BG, Scheib H, van der Weerd L, Young B, McNaughtan J, Ramjan SR, Vidal N, Poelmann RE, Norman JA, 2008. Evolution of an arsenal: structural and functional diversification of the venom system in the advanced snakes (Caenophidia). Mol Cell Proteomics 7:215-246 <link>
Hayes, W. K., S. S. Herbert, G. C. Rehling & J. F. Gennaro, (2002) Factors that influence venom expenditure in viperids and other snake species during predator and defensive contexts. In: Biology of the Vipers: 207-234. G. W. Schuett, M. Höggren, M. E. Douglas & H. W. Greene (Eds.). Eagle Mountain Publishers, Eagle Mountain, UT <link>
Jackson K, 2002. How tubular venom‐conducting fangs are formed. J Morphol 252:291-297 <link>
Kardong, K. V. & T. L. Smith, (2002) Proximate factors involved in rattlesnake predatory behavior: a review. In: Biology of the Vipers: 253-266. G. W. Schuett, M. Höggren, M. E. Douglas & H. W. Greene (Eds.). Eagle Mountain Publishers, Eagle Mountain, UT <link>
Kardong KV, 1996. Snake toxins and venoms: an evolutionary perspective. Herpetologica 52:36-46 <link>
Kuch, U., J. Müller, C. Mödden & D. Mebs (2006). Snake fangs from the Lower Miocene of Germany: evolutionary stability of perfect weapons. Naturwissenschaften 93, 84-87
LaDuc, T. J., (2002) Does a quick offense equal a quick defense? Kinematic comparisons of predatory and defensive strikes in the Western Diamond-backed Rattlesnake (Crotalus atrox). In: Biology of the Vipers: 267-278. G. W. Schuett, M. Höggren, M. E. Douglas & H. W. Greene (Eds.). Eagle Mountain Publishers, Eagle Mountain, UT <link>
Mittleman M, Goris R, 1974. Envenomation from the bite of the Japanese colubrid snake Rhabdophis tigrinus (Boie). Herpetologica 30:113-119 <link>
Pyron, R. A., F. T. Burbrink, G. R. Colli, A. N. M. de Oca, L. J. Vitt, C. A. Kuczynski & J. J. Wiens (2011). The phylogeny of advanced snakes (Colubroidea), with discovery of a new subfamily and comparison of support methods for likelihood trees. Mol. Phylogenet. Evol. 58, 329-342 <link>
Savitzky AH, 1980. The role of venom delivery strategies in snake evolution. Evolution 34:1194-1204 <link>
Shea G, Shine R, Covacevich JC, 1993. Elapidae. In: Glasby C, Ross G, Beesley P, editors. Fauna of Australia. Canberra: AGPS <link>
Vonk FJ, Admiraal JF, Jackson K, Reshef R, de Bakker MA, Vanderschoot K, van den Berge I, van Atten M, Burgerhout E, Beck A, 2008. Evolutionary origin and development of snake fangs. Nature 454:630-633 <link>
Weinstein SA, Warrell DA, White J, Keyler DE, 2011. "Venomous" Bites from Non-Venomous Snakes: A Critical Analysis of Risk and Management of "Colubrid" Snake Bites. Amsterdam: Elsevier <link>
Weinstein SA, White J, Keyler DE, Warrell DA, 2013. Non-front-fanged colubroid snakes: A current evidence-based analysis of medical significance. Toxicon. 69, 103-113 <link>
Weinstein S, White J, Westerström A, Warrell DA, 2013. Anecdote vs. substantiated fact: the problem of unverified reports in the toxinological and herpetological literature describing non-front-fanged colubroid (“colubrid”) snakebites. Herpetological Review 44:23-29.
Wüster, W., L. Peppin, C. Pook & D. Walker (2008). A nesting of vipers: Phylogeny and historical biogeography of the Viperidae (Squamata: Serpentes). Mol. Phylogenet. Evol. 49, 445-459 <link>
Young BA, Dunlap K, Koenig K, Singer M, 2004. The buccal buckle: the functional morphology of venom spitting in cobras. J Exp Biol 207:3483-3494 <link>