Chapter 14. The Value of Snakes

14. The Value of Snakes

Snakes are an enigma, serving as living examples of species that people have tried to eradicate for centuries. Fortunately, the attempts have been unsuccessful in most instances although certain species still are thought to be coiled in the balance of survival or extinction.

                Whit Gibbons, 1983

                A stretch of road, well known to snake collectors, winds through some of the Chihuahuan Desert’s most spectacular landscapes. I drove that road many times long before snakes were popular collectors items. One evening was particularly memorable because my companion and I found more than 70 snakes during a four hour drive. Most of the snakes were Western Diamondback Rattlesnakes (Crotalus atrox), and many of the rattlesnakes we found were headless and tailless. Someone else was looking for snakes on the road that night and well ahead of us. They were taking trophies, probably for the curio trade.

Convincing people that snakes, and the ecosystems that support them, are valuable is difficult. The fact that snakes are aesthetically pleasing, fascinating to contemplate, and provide important clues to understanding the history of tetrapods should be reason enough for people to appreciate and protect them. But if that argument doesn’t convince the skeptical, maybe the economic, ecological, and medical importance of snakes will change their view. As the human population exceeds 7 billion, more natural ecosystems are converted to agro-ecosystems, more pollution is produced, and more habitats are fragmented. In many ecosystems, snakes have become just another source of protein to be exploited.

Snake Harvests

                Siem Reap, Cambodia has the feel of a boomtown. Some streets are paved, but many are not, and people are everywhere. New construction is ubiquitous. Hotels and restaurants are advertising grand openings and the most recent discounts to draw in consumers. The signs are in English and, while the Cambodian Riel is readily traded for goods and services, US dollars are just as easy to spend. The streets are filled with the indigent and poor, many of which are children. Missing limbs and scars from severe burns, presumably from stepping on unexploded land mines buried for decades across the country, are common. Most westerners come to Siem Reap to tour the Angkor Wat ruins which are certainly worth the trip, but we were here for the snake harvest [Figure 14–1]. While exploring the area around the hotel, I saw a familiar-looking pattern lying in the fine dirt of the street. It was a flattened section of a snake’s body; it couldn’t be road kill because both ends were cut clean. The scales had the distinctive shape of those from a Sunbeam Snake (Xenopeltis unicolor).

INSERT FIGURE 14-1.

Figure 14–1. The Tonle Sap snake harvest. A: A young fisher with his gill nets used to catch snakes. B: A pile of snakes, mostly homalopsids, in a Siem Rep market. C: Female Rainbow Mud Snakes (Enhydris enhydris) with their ova exposed. This shows the customers that the snakes have a high fat content.

                Daryl Karns and I were in Siem Reap for a few days to meet with Sharon Brooks and John Reynolds and see the snake harvest. Snake collecting has become a significant human activity around Tonlé Sap, Southeast Asia’s largest lake. Bryan Stuart and colleagues had described the snake harvest and estimated its scale, suggesting huge numbers of snakes were being collected from the Lake. Brooks, Reynolds, and Edward Allison had begun a study of the harvest, collecting information on the snakes involved, and examining the economic side of the harvest’s impact on the local economy and the Lake’s ecology.

                An early morning walk around the Siem Reap market allowed us to observe vendors and customers. Many were selling and buying fish, vegetables, fruits, and household supplies; some were trading snakes. People would pick out the snakes they wanted from a pile two or three feet high. Most of the snakes were the Rainbow Mud Snake (Enhydris enhydris), but the Tonlé Sap endemic Long-tailed Mud Snake (E. longicauda), the Puff-faced Water Snake (Homalopsis bucatta), the Checkered Keelback (Xenochrophis piscator), and the Asian Pipe Snake (Cylindrophis ruffus) were also common among the catch. The vendors would often sit next to their mound of snakes with a cleaver and a wood block and chop the snakes into small pieces. Sometimes the gravid females would have their bellies opened with the ova on display. Pedestrians and cyclists would approach, buy some snakes, and walk or ride off with their purchase in plastic bags.

                Our next stop was Chong Khneas, a port on the edge of Tonlé Sap. A dirt road lined with dilapidated wood-framed houses took us to the docks where brokers brought their snakes. Sacks filled with snakes were being unloaded from the boats and weighed by some of Sharon’s workers. Sharon would buy a sample of the catch, take it to a nearby houseboat and collect data. Species’ composition, body size, sex, food in the digestive system, and reproductive condition were carefully recorded.

                After the market and the port, we hired a boat and took a day tour of the lake. Our first encounter with a snake fisher was a small boy, about 10 years old, paddling a wooden flat-bottomed boat filled with gill nets. One of the boatmen hailed him, and after a few minutes of discussion, he showed us his catch. A half dozen Rainbow Mud Snakes and a Puff-faced Water Snake sat in the bottom of the boat. The boy’s small catch would be sold to a broker who would buy snakes from other fishers and then take them to Chong Khneas or one of the other ports on the lake to sell them to vendors. While exploring the lake, we encountered a fairly large boat with a huge plastic ice chest on the deck. The boat’s inhabitants were children, the oldest not more than 16 years old. We inquired about the chest and they revealed the contents: hundreds of snakes. In addition, the chest contained a wicker plate with several skinned rainbow mud snakes ova exposed, no doubt destined to be part of their evening meal. We encountered numerous people on the lake that day; some were in boats, others had floating houses that rose and fell with the waters of the Tonlé Sap and Mekong Rivers. Some had gill nets, others used a hook and line, and still others used large drop nets set on floating platforms. Upon our return to Chong Khneas, we saw one woman grilling Rainbow Mud Snakes along the roadside. So, at least some of the snakes were being consumed by humans.

                In Siem Reap we knocked on the gate of a house, the nicely landscaped yard was surrounded by a poured concrete wall, suggesting the homeowner was well-to-do. A woman greeted us and, after an exchange in Khmer, we were invited to the rear of the house. In place of a landscaped backyard, there were concrete pools surrounded by wire fences that housed crocodiles. Buckets under a shaded porch contained dozens of baby Siamese crocodiles and some hybrid Siamese x Cuban crocodiles. Brooks and co-workers estimate that 6.9 million snakes (about 777 tons) are removed from Tonlé Sap annually, most of them sold as crocodile food. But some of the larger snakes, particularly the Puff-faced Water Snake and Bocourt’s Mud Snake (Enhydris bocourti), are also collected for their skins.

                Interviews with fishers lead Brooks and colleagues to the realization that the size of the snake harvest declined between 2000 and 2005 by 74–84%, with the two largest species (Homalopsis buccata and Enhydris bocourti) declining the most. The authors also report these were the two species with the lowest fecundity in the harvest. Both species were specifically targeted by hunters because their skins are sold on the international market. Most of the fishers considered snake fishing seasonal work. When asked why they decided to catch snakes, some said it was in response to a declining fish catch, and others said it was because of requests from snake traders. Of the households surveyed 59%, were in debt, usually for purchases related to fishing gear, food, and livestock. Snakes began being harvested for the crocodile farm industry when fish became too expensive to feed crocodiles. Today, the Tonlé Sap fish catch is mostly exported.

                Brooks and colleagues suggest a combination of snake hunting and fishing at Tonlé Sap may better conserve the natural ecosystem than using the floodplain habitats as seasonal agroecosystems. Collecting snakes diversifies the options people have to support themselves. Poorer households depend more on the snake fishery than wealthier households, and it provides a higher income and reduces the vulnerability of the poor to declining resources. Declining fish and snake populations are certainly a threat to Tonlé Sap’s ecosystem and the human that rely upon it, but there is a potentially greater problem.

                Tonlé Sap is dependent on the seasonal flooding of the Mekong River. These waters back up the Tonlé Sap River every year, and the lake expands across the floodplain. Tonlé Sap is about 2,500 km2 of water that expands into 10,000–16,000 km2 of water during its annual cycle. The construction of the Manwan Dam on the Mekong River in China threatens the seasonal flow of water into the lake, something that has been cause for concern in recent years since the fate of the Tonlé Sap, its people, and snakes are closely tied to the dam and the flow of water.

Evidence is accumulating that wildlife harvesting causes changes that can result in a phenomenon that has been called “evolutionary suicide.” Fishery studies suggested that harvesting results in changes in age and size at maturity, reduced population growth rates, and reduced abundance, changes that are distinctly different from what would occur under natural selection. There is evidence that this also true for snake populations.

The pitviper known as the Japanese Mamushi (Gloydius blomhoffii) is widespread in the Japanese Archipelago and has been hunted extensively by local people who consider it a delicacy. It is also collected commercially for use in a virility tonic, a bottle of potato whiskey known as shochu with a snake added. The snakes may also be ground into a powder, mixed with herbs and ethanol, and aged in wooden kegs. The number of snakes involved at the peak of the trade was estimated by Richard Goris to be in excess of a million per year.

Kiyoshi Sasaki and colleagues compared populations of the Japanese Mamushi that had been hunted with populations that had not. Harvested Japanese Mamushi populations had smaller individuals with fewer vertebrae, females produced more offspring, the offspring were smaller at birth, snakes fled at greater distances from humans, and snakes were less likely to show defensive behavior typical for the species. Human predation has selected the hunted populations for a set of traits that would be disadvantageous under natural conditions. Smaller adult female size means smaller offspring, and smaller offspring means a lower survival rate. Fleeing humans at a greater distance means lost opportunities to find food and mates, or bask. Human harvesting has unforeseen consequences for animal populations.

The number of snakes consumed by the Chinese is staggering. Snakes are used for food, pets, specimens, leather, traditional Chinese medicine (TCM), and are a source of ingredients for cosmetics. Zhihua Zhou and Zinigang Jiang of the Chinese Academy of Sciences examined the species involved in the trade and summarized some of the statistics previously published in Chinese. They found reports that estimate 0.8 to 1.0 million snake heads are harvested each year in northeastern China and estimate that 10 to 15 years of hunting prohibition is needed for populations to recover to pre-1985 levels. In the Pearl River port of Guangzhou in Guangdong Province, 1.4x107 kg of snakes are consumed. In case you missed it, that’s 14 million kilograms, or 30.8 million pounds, of snakes. Between 1990 and 1995, 13 factories producing TCMs used 1,600 kg of the Chinese Ratsnake (Zaocys dhumnades), 234 kg of the Chinese Moccasin (Deinagkistrodon acutus), and 20,300 heads and 31.2 kg of the Chinese Banded Krait (Bungarus multicinctus). Another estimate suggested that 9 of the 22 Chinese provinces consumed 7.57 x 106 kg of snakes per annum. Use of snakes in Anhui province increased from 15,000 kg in 1997 to 91,000 kg in 2000. The approximate number of snake heads exported from China in the early 1990’s was estimated to be in the range of 3.0–3.5x106. China has now shifted from being a net exporter of snakes to a net importer of snakes. The country can no longer sustain the use of its native snakes and is now starting to suck-up snakes from the rest of the world. The USA’s part in this is not clear, but between 1998 and 2002 the US exported 72,683 Western Diamondback Rattlesnakes (Crotalus atrox) to be used as food and TCMs by the Chinese. It is important to bear in mind that while the US exported its snakes for food, it also imported Chinese snakes for the production of traditional Chinese medicines

                Chinese medicines using snakes are numerous. Here is an example from the TCM Assistant website. Wu Shao She is a medicine that “Expels wind; eliminates accumulations; calms convulsions; ...” The drug is “…collected in summer and autumn, cut open in the abdomen.” The drug is, in fact, an almost-complete corpse of the Chinese Ratsnake (Zaocys dhumnades). Of course, there is no evidence that any of these TCMs are able to cure any one of anything, unless of course it is by way of the placebo effect.

                Snake skins are also important in the exotic leather trade in the US and Europe. The number of these is difficult to calculate, but it could be well into a million skins per year. Snakes that are a meter or less, including the homalopsids, colubrids, and vipers, are often involved at low levels in the trade. However, the snakes that are in demand are the large pythons, particularly the Reticulated Python (Broghammerus reticulatus), which is heavily hunted in Indonesia. A recent estimate of the number of giant constricting snakes in legal trade imported into the USA between 1977 and 2007 is estimated at more than 1.1 million individual snakes.

Snake Culture

Humans breed many snake species for a variety of colors and patterns, and they produce them in huge numbers for aesthetics and profit. Lucian Heichler and James B. Murphy have declared Johann Mattäus Bechstein the father of herpetoculture. Bechstein authored multiple works on maintaining animals in captivity, including a volume on amphibians and reptiles published in 1797. However, the production of snakes for aesthetically pleasing colors and patterns is a contemporary trend and, I suspect, not within the imaginations of Bechstein. Designer morphs, as they are called, are sold in virtually all pet stores and are extremely popular in the United States and Europe. The herpetoculture of designer morphs is a relatively recent phenomenon but it has roots that may be a century old.The city of Iwakuni, Japan has an area of approximately 102 km along the Nishiki River that supports an albino population of the Japanese Ratsnake (Elaphe climacophora). Shoji Tokunaga and Shigetaka Akagishi considered this the only wild snake population where albinism has become established. They estimated the number of albino snakes to be 1000 in 1925. The snakes occupied houses, storehouses, river banks, and stone walls, and they could be seen in streets, gardens, and fields. In 1924, the snake’s habitat was designated a national monument, but in 1972 the snake itself was given national monument status. The number of albinos declined between 1970 to 1990 and the city of Iwakuni appealed to volunteers to conserve the snake and construct a breeding facility. Considering the Japanese interest in manipulating nature (think bonsai and koi), my opinion is this was not a natural population but one encouraged and protected by the residence of Iwakuni, particularly given the anthropogenetic habitats used by the snakes. It is unclear if residents were actually breeding the snakes early in the 20th century or if the snakes thrived because they were protected by the local people. But given the high estimate of snake density in a relatively small area, captive propagation followed by release seems likely.

A female albino Gopher Snake (Pituophis catenifer) at the San Diego Zoo was bred to a normal male by C. B. Perkins in 1940. Perkins was producing a second generation with (F2) albinos by 1945. And, in 1952 Bernard Bechtel obtained an albino Corn Snake (Pantherophis guttatus) from E. Ross Allen’s Silver Springs, Florida reptile farm and started a colony of albino corn snakes. Also in the early 1950’s, Swiss animal collector Peter Ryhiner obtained an adult leucistic Burmese Python (Python molurus bivittatus) from Pakistan. Ryhiner realized that it was not an albino because it had dark blue eyes and a solid white coloration. The python, named Serata, gained notoriety as the guest of honor at a New York cocktail party reported in The New Yorker magazine, but eventually the snake ended up at the Staten Island Zoo in the care and custody of herpetologist Carl Kauffeld. Today leucism is known to result from a lack of skin pigment, not just the absence of melanin which produces albinism. Leucistic snakes are quite popular in the current pet trade as are albinos, melanoids, hypomelanistics, piebalds, xanthics, axanthics, and many more which have been given a variety of designer names for marketing purposes [Figure 14–2].

INSERT FIGURE 14-2.

Figure 14–2. An aberrant patterned California Kingsnake (Lampropeltis getula).

Interest in color and pattern morphs increased in the following decades and, by the 1980’s, a number of different species of colubrids, as well as pythons and boas, were being bred for color and pattern morph variations. A book published in 2006 attempted to summarize the morphs of medium-sized boas and pythons. It lists more than 200 color morphs and hybrids. But it did not include the morphs of the Burmese Python (Python molurus bivittatus) and the Reticulated Python (Broghammerus reticulatus), which may total another 50 or more designer snakes. Note that the hybrids are usually not hybrids between species, but hybrids between morphs.

The North American Reptile Breeding Conference (NARBC) has three or four trade shows each year. Thousands of people line-up to see and buy the latest designer snakes, some of which sell for $10,000’s. Ball Pythons (Python regius) are by far the most common snakes at the shows, but morphs of many other species can also be seen. Why these snakes should be so popular is something of a puzzle, and many of the people who buy them seem to know little about snakes as organisms. Their interest seems to lie in collecting aesthetically pleasing objects; which, in this case, happens to be live snakes. There is also a certain amount of obsession for some, to have an unusual animal that others don’t have. Possessing rare objects is a desire of many. While snakes are being bred for pets in Western cultures, they are cultured for other purposes elsewhere in the world.

The Vinh Son Commune in the northern province of Vinh Phuc near Hanoi, Vietnam appears to have brought herpetoculture to a new level. A  Kyodo News story (August 6, 2002) reports the Commune started a cobra breeding program in response to the Chineses markets’ demand for snakes. North Vietnamese cobras lay eggs in May and June and they hatch about 60 days later. In 2001, about 90% of the eggs hatched, producing a total of approximately 20,000 snakes. Hatchlings weighed 150–300 grams and reportedly had a winter survival rate of only 20 –30%. The snake breeders decreased winter mortality by setting up a facility in the more tropical Mekong Delta. In 2002, the Commune reportedly produced 50 tons of cobras that were exported to China. A 2007 story from Vietnam News reported that, in addition to the co-operative, 970 of 1,200 households in Vinh Son breed cobras, as do three private enterprises. Apparently the snake business has expanded to produce wine, venom, glue, and protein powder made from snakes. The snake farming activities have been supported by the Vietnam Bio-technology Institute. To be sure, modern medical technology has improved many lives by manipulating human chemistry and biology, and snakes have played a role.

A word of caution, it appears that many “snake farms” are not really breeding facilities to produce snakes; instead they are cover operations for widespread snake harvests. Networks of collectors over a large geographic area are removing snakes from wild populations and funneling them to the so called “snake farms.” I have no personal knowledge that any of the businesses discussed here are or are not engaged in that kind of behavior. For a perspective on this see Maneka Gandhi’s article listed in the References and Notes. The best way to combat this kind of excessive harvesting is to not buy products made from wildlife.

Transgenic Snakes

Transgenic organisms are individuals that carry DNA from another species; they have been produced since the mid1970’s; and are used in medical, agricultural, and scientific research. Microorganisms have been modified to manufacture a variety of proteins. Transgenic mice that emit light have been used for diagnostic and therapeutic tests. Transgenic cattle, goats, and sheep carry genes to produce a variety of industrial and medically important proteins. Transgenic birds are used to produce commercially useful proteins in their eggs. Transgenic frogs are used to detect endocrine disrupters in the environment as well as models for evaluating drug efficacy. Transgenic zebrafish are used in development studies, testing toxic compounds, and as classroom teaching aids. We now have transgenic snakes.

On February 16, 2010, a United States Patent was give to Paul E. Mozdziak, James N. Petitte, and North Carolina State University to produce transgenic snakes. The patent suggests that transgenic snakes would be used for testing repellents, toxicological compounds, teaching aids, and venom production. Mozdziak and Petitte produced transgenic ball pythons, corn snakes, and kingsnakes using a retrovirus as a vector to carry the genes into developing snake embryos.

Snakes and Medicine

                The snake-medicine connection is ancient.  In China, 2000 YBP, shed snake skins were applied to skin diseases, eye infections, sore throats, and hemorrhoids. Snake gall bladders were recommended for similar aliments. Subhuti Dharmananda of the Institute for Traditional Medicine in Portland Oregon listed three features of snakes that attracted the attention of traditional healers: snakes are flexible and fast, they shed their skins, and some are highly toxic. As noted in Chapter 6, there was a thriving business in snakes for 18th century apothecaries in England. And by the end of the 19th century, snake venom was being used to produce antivenom to treat envenomation. Modern medicine has expanded on snake toxins to produce some very useful drugs taken by millions of people who have no idea that their improved health and well being is the result of molecules that evolved in snakes during the last 55 MY.

                An estimated 65 million Americans have hypertension (high blood pressure); if uncontrolled, it results in kidney and brain damage as well as fatal cardiovascular diseases. Captopril®, Enalapril®, and Lisinopril® are drugs that are commonly known as ACE (angiotensin-converting enzyme) inhibitors. These molecules are based upon a peptide discovered by Sergio Ferreira and M. Rocha de Silva at Brazil’s Instituto Butantan in 1961; the peptide was from the venom of the Jararaca (Bothrops jararaca). Capoten® (Captopril®) was approved for use in treating hypertension in 1981, and the drug became a generic in 1996. Other forms of the molecule followed and in 2005, more than 150 million prescriptions were written for ACE inhibitors. Today, these drugs are among the top 20 best selling in the world, and they owe their existence to a Brazilian pitviper who successfully evolved a peptide to effectively lower the blood pressure of its prey.

                Blood clotting disorders increase with age and sedentary lifestyles. Blood clots form in veins, often in the lower extremities, and move into other parts of the body where they block blood flow. Observations that venom of the saw-scaled viper (Echis) causes excessive bleeding lead to the isolation and development of a molecule called Tirofiban. The chemical is now marketed as Aggrastat®, which prevents blood clots by inhibiting platelet aggregation and the subsequent heart attacks and strokes they may cause. The origin of the molecule is often cited as being from Echis carinatus. However, E. carinatus is now a species restricted to the Middle East and South Asia. Thus, the snake that this molecule originally came from was probably one of the African species: E. leucogaster, E. pyramidum, or E. ocellatus.

                Also used for clotting disorders is Batroxobin, a serine protease enzyme isolated from the venom of the Brazilian Lancehead (Bothrops moojeni). Note that this snake was formerly considered a subspecies of B. atrox hence the name, Batroxobin. Batroxobin is marketed under a variety of names for a variety of blood disorders as well as diagnostic tests. It converts fibrinogen to fibrin by cleaving only fibrinopeptide A from the parent fibrinogen molecule. It is used as a plasma-clotting agent for fibrinogen and for the detection of fibrinogen degradation products. It is sold under the names: Reptilase®, Reptilase time (RT), and Reptilase® ST. Batroxobin is also used in Botropase® for control of bleeding, and Defibrase® for control of deep vein thrombosis, pulmonary embolism, peripheral vascular disease, angina vein thrombosis, and acute ischemic stroke.

                Ancrod is an anticoagulant from the venom of the Malayan Pitviper (Calloselasma rhodostoma). Ancrod, an enzyme, acts directly on fibrinogen by cleaving it to prevent clot formation and reduces the viscosity of blood to improve blood flow. It has been sold under the names Arwin®-Knoll, Arvin®, and Venacil®. Neurbiological Technologies has used Ancrod to develop their drug ViprinexTM, a molecule used to limit brain damage after an acute ischaemic stroke.

                Eptifibatide is sold under the name Integrillin® and is derived from a protein in the venom of the Dusky Pygmy Rattlesnake (Sistrurus miliarius barbouri). It reversibly binds to platelets and reduces the risk of acute cardiac ischemic events in patients with unstable angina or myocardial infarction.

                Molecules from snake venom are also being recruited for controlling cancer. Francis S. Markland at the Keck School of Medicine examined the venom from the Copperhead (Agkistrodon contortrix) and found a disintegrin he named contortrostatin. Disintegrins are molecules that bind to integrins, a group of transmembrane receptor proteins involved in cell adhesion. One of the functions of integrins is to provide traction for cells, allowing them to migrate. An integrin called {alpha}v{beta}3 is found on the surface of cancer cells and is involved in metastasis. Markland studied contortrostatin's anticancer properties and found it kept cancer cells from spreading, but it also kept blood vessels from growing into the tumor and nourishing cancer cells. It has been tested on breast cancers as well as prostrate cancers and found effective. A drug based upon this molecule is still in development. Dong Ju Son and colleagues found a molecule in the venom of the Turna Blunt-nosed Viper (Macroviper lebetina turanica), that inhibits growth of human prostate cancer cells by triggering apoptosis (cell death).

                In August of 2009, XenaCare was awarded the exclusive license for marketing and distributing Cobroxin TM. An over the counter drug made by Nutra-Pharm, Cobroxin TM is expected to become the alternative to current opiate and acetaminophen-based analgesics for the treatment of chronic pain. According to Nutra-Pharm’s website, CobroxinTM was first developed as an analgesic in 1978 from the venom of the Chinese Cobra (Naja atra) and was produced by the Kunming Institute of Zoology. A modified version of this neurotoxin was marketed in 2000. The new drug is a mixture of cobrotoxin, ibuprofen, and Qu Ma Du (believed to be Tramadol, a narcotic analgesic with a low-addictive potential). The new Cobroxin TM reportedly takes effect faster than alternatives and is longer lasting and safer. Cobroxin TM is now also used to treat drug addiction in the Chinese province of Yunnan. The National Cancer Institute in Italy has participated in Chinese clinical trials to assess the efficacy of cobra toxins in controlling post-operative pain and moderate to severe cancer pain. More recently, Cobratoxin has been reported to kill mesothelioma and lung cancer cells. The pain-killing nature of this venom molecule was first reported in the medical journal Lancet in 1933. Venom fractions with analgesic properties have also been reported from King Cobra (Ophiophagus hannah) venom (hannalgesin), and from the venom of the tropical rattlesnake known as the Cascavel (Crotalus durissus terrificus) (crotalphine).

                Snake venom is also used to make diagnostic test kits, Reptilase®, Reptilase time (RT) and Reptilase® ST have already been mentioned. Pentapharm Ltd maintains a large snake breeding facility in Minas Gerais, Brazil capable of housing 10,000 snakes. The facility was created in hopes of providing a source of quality controlled venom from the lanceheads, Bothrops atrox and B. moojeni. They make Pefakit® PiCT (Prothrombinase induced Clotting Time) used to monitor anticoagulants such as heparin and PC-R Factor V Leiden, which is used to screen for the factor V Leiden mutation genotype.

                Snake venom toxins offer possibilities for numerous types of medications for human diseases. There has been a long-running controversy over using cobra venom to treat multiple sclerosis (MS), with anecdotal reports suggesting cobra venom is beneficial for MS patients. Paul Reid of ReceptoPharm Inc. reviewed the literature and found that in the early 1900’s, cobra venom was used to treat severe pain, rheumatism, trigeminal neuralgia, asthma, and neuroses. The venom was heated prior to use, denaturing the enzymes but leaving the peptide toxins intact. Both Cobroxin and Nylonix were marketed until 1972 for pain and arthritis, at which time the FDA rules regarding drug registration changed and the products were abandoned over production issues and in favor of newer molecules.

                In the mid-1970’s, Ben Shepard, a pediatrician and Dade County Florida medical examiner, was suffering from rheumatoid arthritis. He treated it with Venagen/PROven, a mixture of raw cobra, krait, and viper venoms produced by William Haast at the Miami Serpentarium. Shepard, impressed with the results, established a foundation devoted to treating arthritis and MS using snake venom. Over the next several years, Shepard treated 7000 people with the snake venom mixture for arthritis, MS, and shingles. The research did not have FDA approval and lacked clinical controls. Upon his death in 1980 the FDA closed his clinics.

                Modified neurotoxin (MN) from cobras was used by Murray Sanders to treat polio. Sanders, an Assistant Professor at the University of Miami, was also influenced by William Haast at the Miami Serpentarium, and obtained funding through the March of Dimes. The research did have controls, but was poorly designed. However, the results suggested patients who continued treatment survived an average of 15 months longer than those people who had discontinued treatment. MN was also examined for antiviral properties. Polio, pseudorabies, and rabies viruses all target motor neurons and are associated with MS. Reid found that detoxified cobratoxin (MCTX) and MN have excellent safety records and almost no side-effects in humans, that they may offer protection to nerves, and are prime candidates for controlled clinical studies with MS patients.

                In addition to the important role venom components play in medicine, the cosmetics industry may have uses for these molecules. PentaPharm markets a wrinkle cream called ProLux with the active ingredient SYN@-AKE, a synthetic molecule based on a peptide (Waglerin-1) found in the venom of Wagler’s Pitviper (Tropidolaemus wagleri). Apparently, this snake-derived molecule is also being used in other wrinkle creams sold under a variety of names. Snakes and snake venom are valuable resources.

Snakes in Modified Ecosystems

                The role of snakes in ecosystems is complex, they are predators and prey, they are affected by changing environments, and they bring about changes in environments. Snakes impact biodiversity and their presence may be used as an indicator of ecosystem health. As predators on small mammals, they may act to control populations of species capable of transmitting viral and bacterial diseases to humans. We know relatively little about the more subtle roles snakes play in the environment, but there are a few studies that point towards the influences snakes have in the web of life and how small changes may have unforeseen consequences. The impact of Brown Treesnakes on native Guam pollinators was previously discussed, but there are other examples.

                Snakes may alter the social behavior of other animals through predation on a specific age group or gender. Lowell Getz and colleagues found breeding units of the Prairie Vole (Microtus ochrogaster) consisted of an extended family. Voles breed in April and again throughout September and October. Spring breeding groups averaged 1.9 individuals, often a single female while the fall breeding groups contained an average of 4.8 individuals. Getz and co-workers suspected predation by the Western Fox Snake (Pantherophis vulpinus) and the Prairie Kingsnake (Lampropeltis calligaster) were responsible for increased spring mortality and the larger fall nesting groups. The authors enclosed a study area to exclude snakes but allow the voles access through gated boxes. Other predators such as feral cats and raptors could access the enclosure from above. The survival of adults in and out of the snake-excluded area was the same, but the survival of juveniles in the snake-excluded area was higher than outside. Snakes were actively preying on the nestling voles in the spring, but not in the fall before they entered hibernation. Larger, fall-breeding groups and a higher survival rate of vole pups was the result.

                As predators, the presence of snakes is directly dependent upon their prey. Kathleen Matthews and co-workers surveyed more than 2,100 high elevation lakes in the Sierra Nevada Mountains and found a close correlation between amphibian presence and garter snakes. The disappearance of amphibians in these environments has been linked to the introduction of a highly invasive non-native trout. They predicted that lakes lacking amphibians would also show an absence of their predator, the Mountain Garter Snake (Thamnophis elegans elegans). And, not surprisingly, that is what they found. Lakes with amphibians were 30 times more likely to have snakes than those without amphibians. A similar correlation between amphibians and snakes was found in Central American stream ecosystems by Matt Whiles and co-workers. Declining amphibian populations, heavily impacted by the chytrid fungus, resulted in rapid declines of frog-eating riparian snakes. With the disappearance of the frogs, other species previously seen with regularity on stream surveys also disappeared.

                Snakes can be impacted by invasive plant species as well. Lucas Hall and colleagues trapped Yellow-bellied Racers (Coluber constrictor mormon) and Great Basin Gopher Snakes (Pituophis catenifer deserticola) on Antelope Island, Utah. The relative abundance of the snakes was negatively impacted by the presence of Cheatgrass (Bromus tectorum), a Eurasian annual plant that grows in dense clumps. Populations of several small mammals, birds, and one lizard had previously been shown to be negatively affected by this plant, and the authors suggest that its dense growth may be a barrier to normal snake locomotion.

                The presence of large, grazing mammals may also influence snake density indirectly. In the Kenyan savanna, Douglas McCauley and co-workers measured the abundance of the Olive Hissing Snake (Psammophis mossambicus) and rodents in plots with and without large herbivores. Rodent burrows were more abundant in the plots that excluded grazing animals as were the Psammophis. The snakes appeared to be responding to the greater number of prey species, and not to the reduced chances of being trampled or reduced predation because of increased vegetation. Studies on the impact of horses on squamate reptiles have shown that snakes and lizards have lower abundance in areas grazed by horses than in areas not used by horses.

                Snakes living in rainforests are adapted for cool, wet, shady environments. These species tend to disappear as the forest is cut and snakes adapted to more open, warmer, and drier habitats move in. Most often these species are savanna-dwelling snakes. Adam Freedman and colleagues studied three widespread African savanna snake species that were also associated with rainforest. However, they occur only at rainforest locations that had been disturbed by humans. Using computer modeling, the authors attempted to predict which of the three species of savanna snakes would occupy deforested sites with a changed climate. Using the Night Adder (Causus maculatus), the Olympic Lined Snake (Dromophis lineatus), and the African House Snake (Lamprophis fuliginosus) as models, they suggest that, despite the increase in open, savanna-like habitat, these snakes may not be able to expand their distributions because of increased rainfall. Their results points to the complexity of trying to develop conservation strategies for biodiversity.

                Species able to adapt to urban environments can be expected to do well in the future. In the eastern USA, the Northern Water Snake continues to exist and apparently thrive in urban wetlands and riparian situations. Abigail Pattishall and David Cundall radio tracked 50 Nerodia sipedon in eastern Pennsylvania for 29 months. The snakes were located 2,520 times, but they were found at only 113 locations. Of these locations 64, were urban and 49 were natural. The urban snakes were feeding on the non-native Brown Trout (Salmo trutta) and using piles of scrap metal and concrete, holes in a railroad bed, and dead coniferous trees inserted into a bank to prevent erosion, as habitat. Pattishall and Cundall suggested that the urban environment provides resources that offset any dangers that might be associated with living with humans.

                Robert Zappalorti and Joseph Mitchell collected observations on 13 species of snakes in urbanized habits in New Jersey over 25 years. They found snakes were able to exploit urban areas if there were corridors of habitat that allowed them to move between patches of suitable habitat. They were also able to adapt because prey was present at high densities. Open habitats allowed the snakes to bask. Human-made hibernation sites were also important. Therefore, at least some species of snakes may be able to survive alongside humans in urban area. 

               

Snakes and Global Warming

                The discovery that Burmese Pythons (Python bivittatus) were living and breeding in the Florida Everglades could have been predicted based on the number of these snakes in the pet trade. They have been imported for many years and are now bred in captivity in many countries, including the USA. A quick check of the Florida Museum of Natural History’s database shows a Burmese Python was collected in Florida on December 12, 1995. Since that date, the number of Florida specimens of this giant snake has steadily increased. The Everglades National Park web site contains a table that shows the number of Burmese Pythons removed from the Park in 2000 was only two. In 2008, that number was 343.  The Florida Museum of Natural History’s collection also contains specimens of the Reticulated Python (Broghammerus reticulatus) and the African Python (Python sebae) collected from southern Florida. Again, this can’t be considered much of a surprise. All are species that have been imported for the pet trade for many years and are bred in private collections. It seems probable that they, too, will soon establish in peninsular Florida, if they have not already done so.  These three python species are three of the four largest living snakes, all are known to exceed 6 m in length.

                In February of 2008, Gordon Rodda of the Invasive Species Unit of the USGS in Fort Collins, Colorado and colleagues issued a report that predicted the distribution of the Burmese Python in the year 2100, given the expected changes in the mean annual temperatures and precipitation during the remainder of this century. They wrote,

By the year 2100, projected areas of potential suitable climate extend northward beyond the current limit to include parts of the states of Washington, Colorado, Illinois, Indiana, Ohio, West Virginia, Pennsylvania, New Jersey, and New York. Thus a substantial portion of the mainland US is potentially vulnerable to this ostensibly tropical invader.

                This was met with both hysterical and skeptical overreaction from the public, particularly from the segments of the population already in denial of the global warming phenomenon. But the report also met with criticism from the scientific community. R. Alexander Pyron and colleagues responded with a niche modeling study that claimed the python will not be able to spread from its current US distribution because the environment favorable to the ecological niche this snake fills is expected to decline.

                Once an animal population has become established, it is very difficult to reduce its numbers to zero. Just consider the effort that has been put into to trying remove the Brown Treesnake from Guam, a relatively small island. As for the expanding python population, my limited field observations with P. molurus in Thailand suggest that it inhabits and reproduces in agroecosystems as well as areas of urban sprawl. Feral cats and dogs as well as free-ranging poultry and rats are readily taken by this snake which does not hesitate to forage near human habitations. The suggestion that it will be contained in southern Florida because of its limited niche requirements is an underestimation of this highly adaptable, broad niche predator. Today, the only established population outside its natural distribution is in south Florida. However, stray specimens that have escaped or have been released turn up all over the country. As the climate warms, it seems probable that other populations will become established as well; thus, this species will not necessarily have to disperse out of south Florida. There is evidence, although limited, that snakes are indeed responding to global warming.

                The Montpellier Snake (Malpolon monspessulanus) is a large (2 m) snake of the Mediterranean region that inhabits open, dry regions. It feeds mostly on lizards but will consume other snakes and mammals. Malpolon has rear-fangs, venom, and has been described as an “elusive super-predator.” Gregorio Moreno-Rueda and co-workers collected data on 334 specimens in southeastern Spain between 1983 and 2004. During the study period, the mean annual temperature of the study area increased an average of 1.54ºC, and the authors found the annual activity period of the snake increased with the temperature. Once adjustments for elevation and precipitation were made, the snake’s activity period lengthened. Based on this data, it seems likely that as the average annual temperature increases, temperate snakes will be active for longer periods of time during the year. Species that are adapted to warmer climates may also be expected to expand their distributions northward where suitable habitats can be found. 

                Given the plasticity of snakes and their dependence on temperature, it seems probable that, as the climate warms, temperate species will not only stay active for longer periods of time, but they will be feeding more often and maturing earlier. Likewise, juveniles may have a higher survival rate and, therefore, populations may increase and geographic distributions can be expected to change.

In an effort to predict the impact of global warming on European amphibians and reptiles Miguel B. Araújo and colleagues modeled distributions using four different species-climate envelope techniques and suggest that many species will expand their distributions if dispersal is unlimited. The exception seemed to be in southwestern Europe, where expanding arid conditions are expected. Although, Araújo and colleagues caution that, limited dispersal opportunities may increase species vulnerability to extinction.

Are Snakes in Decline?

                Snakes are secretive, cryptic, and may live at very low population densities. These traits make snakes difficult to find and, therefore, very difficult to count. Snakes also tend to have restricted distributions, small home ranges, low dispersal ability, low frequency of reproduction, and limited prey species – traits that make them very susceptible to disturbances in the environment and extinction. Science currently recognizes about 3,300 species of snakes, but dozens of new species are described each year and it seems likely that the number of actual species of snakes will double. Many of the 3,300 species are known from one or relatively few specimens, some of which were collected many years ago from localities whose habitat has been radically altered by deforestation, wetland draining, or instillation of agroecosystems.

                Levi Terribile and colleagues analyzed the distribution of the vipers and elapid snakes and, in a second paper, looked at conservation strategies for these two snake clades. They examined the relationship between snake distribution and the actual evapotranspiration (AET) and biogeographical regions. The AET was considered a summary of current environmental conditions, while the biogeographical regions represented the effects of evolution. The distribution and species richness of vipers was more closely correlated with AET, and it explained almost 46% of the variance in species richness. Elapids, on the other hand, had almost none of their species richness explained by the AET, but 57% of their variance was explained by biogeographic regions. The team suggested that this in part results from the fact, that vipers are a much older clade than the elapids.

                Given the importance of snakes in ecosystems, their potential importance to humans as a source of molecules useful in maintaining human health, and for the ecological services they provide, it would seem wise to conserve snakes. But monitoring populations over long periods of time is difficult and expensive. Xavier Santos and colleagues proposed a cartographic approach to determining the status of snakes in the Iberian Peninsula. Plotting old and new literature citations for eight species of snakes in Universal Transverse Mercator (UTM) 10 x 10 km squares, they calculated two indexes. The authors first calculated the percent of new citations (1998–2002) divided by the total citations for that species, a low number suggesting the species is in decline. Secondly, they looked at the percentage of squares with both old and new citations. A low value for a species indicates the potential for extinction. They compared their method to that of an earlier study examining ecological and distributional data as well as factors known to influence snake survival. Santos and co-workers found considerable agreement between the two methods. The lowest scores produced by the cartographic method were for Lataste’s Viper (Viper latasei), the Southern Smooth Snake (Coronella girondica), and the False Smooth Snake (Macroprotodon brevis). Techniques such as this one used to determine species’ vulnerability to extinction will be employed more frequently as habitats are fragmented and destroyed.

                Trees are important resources for humans and wildlife, and deforestation is a serious problem for both. While trees provide habitat structure for species that live above ground, they also control the habitat on the ground below the canopy. Brian Todd and Kimberly Andrews used four experimental forest-management landscapes to study the impact of forest harvesting on six species of small snakes that live in the leaf litter and upper layers of soil. The study was done at the Savanna River Site in South Carolina run by the the U. S. Department of Engery. The study included a clear cut forest with the course woody debris removed, a clear cut site with course debris left on the ground, a thinned stand of pines that had been planted, and a control area of unharvested secondary growth forest. Todd and Andrews obtained results that showed the clear cut study areas had the lowest abundance of snakes, but the thinned pine stands supported the greatest numbers of snakes, more than the older secondary forest used for a control. Clear cut forests have long been considered highly detrimental to wildlife, but selective cutting has been shown to be beneficial to many forms of wildlife, including snakes. Thus, selectively cutting trees may benefit biodiversity, at least in the short term.

                Southern Florida’s mangrove forest is being destroyed for real estate development. It supports populations of a unique natricid snake adapted for life in salt water, the Mangrove Salt Marsh Snake (Nerodia clarkii compressicauda). Kevin Jansen and colleagues found this snake’s population was fractured into isolated neighborhoods of coastal habitat 50–80 km long. While they found the snake to be locally abundant, populations are becoming genetically isolated through habitat fragmentation. Jansen and colleagues suggested that without conservation measures, this could lead to greatly reduced populations and inhibit the ability of the snakes to adapt.

Eleven species of snakes have been reported to inhabit the tall grass prairies of Illinois. Nicolette Cagle surveyed 22 sites in six tall grass prairie preserves in northern Illinois. In a two year study employing drift fences and funnel traps as her collection method, Cagle collected 120 snakes representing seven species. Using anecdotal evidence, she found a 70% decrease in snake abundance had occurred since the mid-19th century.

                One of the snakes missing from Cagle’s study was the Massasaugua (Sistrurus catenatus), a prairie snake that uses specific microhabitats. Daniel Harvey and Patrick Weatherhead used 34 snakes with radio transmitters to examine the microhabitat used by a population in Ontario. Snakes used habitats that had retreats and shrubs close by, and gravid females were found in areas with rocks and a more open canopy compared to non-gravid females and males. Hibernation sites were forested and summer habitats were open, often wetlands, and forest edge habitats. In northeastern Illinois, the Eastern Massasaugua is barely hanging on. It is found in scattered patches of habitat in the Chicago area and the decision was recently made to collect snakes and initiate a captive breeding program. The initiative is called “The Grass is Rattling” and the effort involves the US Fish and Wildlife Service, the Illinois Department of Natural Resources, and the Lincoln Park Zoo. The zoo is doing the work of establishing a captive population that will eventually be used to re-establish wild populations.

                However, the reintroduction and transplant projects that have been done with snakes to date have not been particularly successful. Bruce Kingsbury and Omar Attum summarized 12 projects using nine species that involved repatriation of snakes. Reintroduced snakes had mostly low survival and high mortality. And they note that we currently lack the understanding needed to make snake repatriations successful.

                The Eastern Diamondback Rattlesnake (Crotalus adamanteus) is one of the largest North American snakes, and the largest rattlesnake. Jayme Waldron and co-workers found the Eastern Diamondback to be a remnant species of the pine-savanna. Eastern Diamondbacks are associated with open canopy areas that are threatened because of the exclusion of fires that allowed trees to grow larger and become more numerous. Pine-savanna is a fire-maintained community and the snakes rely on the open habitats for survival. Thus, the use of controlled fires in pine-savanna could benefit the Eastern Diamondback population.

                The Eastern Kingsnake (Lampropeltis getula) also appears to be in decline throughout portions of its range, though the reasons are unclear. Seth Stapleton and colleagues compared two studies, one done between 1976 and 1983 and a second from 2002 to 2005, at three locations in northern Florida and southeastern Georgia. The first survey recorded 10 species of non-venomous snakes totaling 119 individuals, 24 of which were Eastern Kingsnakes. The second study, although shorter in duration, was more intensive in terms of trap-days. It produced 2,310 snakes representing 16 species, but only one was an Eastern Kingsnake. Another bit of evidence that kingsnakes are disappearing comes from a study on Bob-white Quail (Colinus virginianus). Between 1999 and 2007, video cameras monitoring quail nests at sites in northern Florida and southeastern Georgia did not record one instance of nest predation by the Eastern Kingsnake, while the same kind of study done in the vicinity of Albany, Georgia between 2005 and 2006 reported Eastern Kingsnakes were responsible for 40% of the quail nest predation incidents.

                Landscape changes can dramatically impact snake populations but their consequences are not readily anticipated.  The Argentine Boa (Boa constrictor occidentalis) is endemic to the dry forests of the Gran Chaco region of Argentina. Gabriela Cardoza and Margarita Chiaraviglio evaluated the impact of deforestation on the reproduction of the boa. They compared snakes from forests and shrublands for a variety of reproductive parameters and found shrubland populations reproduced less often, mating aggregations were substantially smaller, male body condition was poorer than those from forests, fewer females were in reproductive condition, and females overall wre in poorer health. Landscape changes may increase marginal habitats for snakes where they may survive for a time before they become extinction.

                Building roads fragments habitat. While many snakes will cross roads, there is at least one species that seems reluctant to do so, the Prairie Kingsnake (Lampropeltis calligaster). Matthew Richardson and colleagues radio tracked 10 adult L. calligaster and found them underground 73% of the 574 times they were located. Males had home ranges that were four times larger than female home ranges and, when they mapped home ranges, all had a road that bordered part of the range. Additionally, the authors documented a snake crossing a paved road only once. Besides the reluctance to cross roads, this snake avoided agricultural fields, preferring grasslands. Considering that much of the Midwestern USA is composed of agricultural landscapes divided by roads, the future of the Prairie Kingsnake does not look bright.

There is little doubt that habitat destruction is the major culprit in the decline of many animals, including snakes. Miguel T. Rodrigues notes that Brazil has 330 snake species and only five are considered endangered despite widespread deforestation. He suggests that extreme rarity and highly restricted ranges exacerbate extinctions and that protected areas are the key for conserving Brazil’s reptiles. Much of what remains of natural habitats are isolated fragments similar to those reported for other countries. Much of the habitat destruction is the direct result of lands use, and the majority of the changes in land use are for agriculture. Raquel Riberio and colleagues examined the impact of land use on reptile communities in Spain and, again, linked agriculture as causing the most damage to biodiversity, in this case reptile communities.

Like it or not, humans are in direct competition with most of the world’s fauna for land. As our population exceeds 7 billion people demanding food, water, and other resources, more land will be converted to agro-ecosystems. Given this situation, the future of snakes, other reptiles, and much of the rest of the vertebrate fauna,― including humans,― is bleak.

                Educating the public is the most obvious way of overcoming the issues people have with snakes. Encouraging children and adults to hold harmless snakes in order to become familiar with these animals and desensitize the negative feelings they associate with them, and will do much to improve the chances of conserving snakes. The herpetoculture industry and the local and regional herpetological societies have an important role to play here.  

                Herpetoculture can be a positive force; it increases people’s interest in snakes, and should translate into a deeper interest in snake conservation and concern for the environment. Also, captive propagation of snakes can reduce the hunting pressure on wild populations. But I will never forget one designer snake breeder bragging about the production of a particular color morph, how it was his morph, and that he had made it. Being proud of one’s accomplishments is important, but it is equally important to recognize that this breeder didn’t “make” anything. He simply manipulated sperm and eggs by controlling which males mated with which females over several generations, an activity humans have been carrying out for thousands of years to produce domesticated animals and plants. Manipulating nature as we do for domestication may greatly benefit humans. However, we must be cautious not to lose sight of the fact that humans still depend upon the biosphere for survival. Our control of nature is limited. Just as the snake charmers believed they could resurrect the dead, herpetoculturists should not fool themselves into thinking their accomplishments are more than what others have done with domesticated animals. Altering nature seems to be part of the human character, but we need to do so with forethought and caution.

                While legislation attempts to protect species, it has been mostly a failure. The only sustainable way to protect biodiversity is through education and the heavy regulation and enforcement of industries that continue to exploit natural resources at the expense of the rest of us. Ironically, the only sincere enforcements and regulations currently in action are those directed at researchers. It is much easier for governments to regulate politically impoverished scientists than the politically powerful developers, and they do. Needless to say, this only exacerbates the problem.

                Humankind is facing the most serious threat to its existence ―climate change and the associated mass extinction of biodiversity and social upheaval that will accompany it. How we deal with these challenges will, with luck, show that our choice is to protect life on Earth, including snakes.