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Issue link: http://mag.outdoornebraska.gov/i/946863
PHOTOS BY DAN FOGELL the same snake during different times in its life ... all depending on prey type. Snakes that eat mammals, such as rattlesnakes and other vipers, generally produce a blend of hemotoxins, cytotoxins and cardiotoxins. Mammals have warm bodies and high metabolic rates with high blood pressures. Toxins entering the blood stream will rapidly be delivered throughout the body and upset organ function, which will quickly stop the prey from moving. And the panic caused by being struck will increase blood pressure and make it happen even faster. Snakes that eat lizards and other snakes, such as cobras and coral snakes, have venoms in which neurotoxins predominate. Because they are ectotherms ("cold-blooded"), lizards and snakes have low metabolic rates and blood pressures. Venom isn't going to move as quickly through the blood, and a lizard struck by a hemotoxic snake can travel a long distance before it finally stops. This makes it hard for the snake to catch up with and find its prey. But neurotoxins directly affect the nervous system and can immobilize prey quite rapidly – regardless of their body temperature or blood pressure. While venom is an effective tool for killing or at least immobilizing prey, it also has an equally important second function: digestion. Everyone knows snakes can swallow enormous prey, sometimes equal to half of their own weight. When they do, they get a great big lump in their bellies. Imagine that you weigh 150 pounds and you just ate 30 pounds of food, which is fairly equivalent to a snake's body mass to prey ratio. How easy would it be to move afterward? Consider that snakes crawl around on their bellies. Having that big food lump makes them quite vulnerable and makes locomotion difficult. Escaping predators, evading uncomfortable environmental conditions, even just finding a place to rest is cumbersome. Venomous snakes have an advantage. Besides having toxins, their venom yields a cocktail of digestive enzymes similar to those used by our own digestive system. When injected, the venom not only immobilizes prey, but it also begins digesting it from the inside. By the time the snake completely devours its food digestion is well underway, and once in the digestive tract prey will start being digested from the outside as well. The increased digestion rate reduces the vulnerability period after a large meal and hastens their return to mobility. The third function of venom is the one everyone assumes is its primary function: defense. All snakes tend to bite when defending themselves. Honestly, though, what else can they do? Their teeth are their only real weapons. Venomous snakes just happen to have a refined set of teeth with a built-in venom delivery system. Snakes can control venom delivery during a bite. But manufacturing venom is expensive, energetically speaking, so they generally choose not to use it on a defensive bite unless they are strongly provoked. But the point is that they have it. And they know it. And they will use it if they have to. In the U.S., about 8,000 people annually – mostly males aged 18-35 – are bitten by venomous snakes. Only five or so are fatal cases (low, compared to bee stings at more than 100 per year), resulting in a 0.06 percent death rate. So, there is no doubt that snake venom can be deadly. But researchers are finding that many chemical components of venoms can also be beneficial to humans. Chemicals like procoagulants (which encourage blood clotting) and anticoagulants (which inhibit blood clotting) have been isolated from venoms and are being used to treat patients with blood clotting disorders. But the most promising medicinal uses of venom may help treat and even cure cancer patients. Venom from the copperhead – a Nebraska native species – yields a unique chemical known as contortrostatin (named after the scientific name of the copperhead, Agkistrodon contortrix). This protein interacts with cancer cells and prevents them from attaching to other cells and tissues. It also hinders their formation of new blood vessels (called angiogenesis) which would help them leave their "home" tissue. The result: an inability to spread. And experimental trials have shown a significantly lower risk of metastasis in the presence of contortrostatin. Venom from at least three other snakes is also being tested for potential cancer treatment. We have traditionally looked at snake venom as a deadly threat. And venomous snakes are still dangerous and should be respected as well as avoided whenever possible. But just as plant toxins have been studied, tested, and incorporated into human medicine, snake toxins will likely be used in future medicinal treatments. In fact, there may soon come a time when snake venom saves more lives than it takes. ■ Venomous snakes usually cause fear when encountered, but many – like this copperhead – produce venoms that may save more human lives than they take. MARCH 2018 • NEBRASKAland 45