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Slithering States: Areas with Changing Snake Populations

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As Washington squabbles over health care and financial reform, another political disagreement is slithering under most Americans’ radar: snakes. Snakes on a plane and snakes in the wild. Native snakes and invasive snakes. Venomous snakes and snakes that are just really, really big.

The vast majority of Americans don’t live in the same areas as dangerous snakes. But in three heavily populated states, Florida, Texas, and California, changing snake populations are altering how—and how often—we encounter our legless reptilian friends.

Florida is rolling in reptiles, but it’s unlikely you’ll be killed by one. The odds that a person in Florida will die from contact with a venomous snake or lizard in a year are 1 in 38,970,000. And the type of snake that seems to be taking over isn’t even venomous.

Burmese pythons, native to India, lower China, and the Malay Peninsula, have been swamping Florida Everglades National Park for the last few years. The snakes are popular pets: According to the U.S. Geological Survey, more than 300,000 of them have been imported into the U.S. in the last thirty years. Keeping pet pythons is legal in the U.S., but releasing them isn’t. Yet overwhelmed python owners often set the snakes free when they near their fifteen-foot potential. They’re top predators who adapt easily to a wide variety of habitats, hence their rapid spread through south Florida.

What’s so bad about pythons on the loose? Although there was a recent tragic case of a Florida toddler asphyxiated by a pet python, their threat to human life is minimal. The same can’t be said about their threat to native Florida wildlife, like the Key Largo woodrat, the American alligator, and the wood stork. An invasive species, the python is able to prey on Florida’s native fauna because those animals have not yet evolved defenses against the snake.

The U.S. Fish and Wildlife Service recently proposed a rule to list the python, along with nine other invasive giant constrictor snakes, as “injurious wildlife.” If adopted, the listing would prohibit the importation or interstate transportation of the Burmese python and its eggs, except for academic or zoological purposes. That’s where the politics comes in: Republican lawmakers claim the new regulation would hurt business, causing “severe economic pain for thousands of Americans by destroying livelihoods.”

In the Lone Star State, it’s not snakes that are on the rise, it’s snakebites. According to a 2009 report from the Texas Office of the State Climatologist, increasing temperatures and chronic drought in Central Texas have driven snakes from their dens into residential areas, where the snakes search for water in recently watered lawns and gardens. And where there are people, there are mice, a snake favorite.

The snakes’ increased presence in populated areas seems to have upped the number of snakebites. In 2009, Ben Copwood, a General Surgeon at the University Medical Center at Brackenridge, noted a dramatic spike in the number of snakebites treated at the Medical Center: thirty-six bites at the end of June 2009 compared to an average of just fifteen to seventeen bites annually in previous years.

And these bites can, on occasion, be deadly. Many of Texas’ snakes are venomous. Of the 250 snake species in the U.S., only four are venomous, but Texas has all of them: the copperhead, the rattlesnake, the cottonmouth, and the water moccasin. Still, the odds that a person in Texas will die from contact with a venomous snake or lizard in a year are just 1 in 30,420,000.

For the past few years, California’s Southern Pacific rattlesnake has been the focus of myriad news stories suggesting the snake is rapidly evolving super-toxic venom. The theory seems to have come from the impressions of a handful of Southern California physicians and toxicologists who have reported a rise in both snakebites and snakebite severity. These physicians speculate that Southern Pacific rattlers are becoming more aggressive and may be crossbreeding with the Mojave green rattlesnake, a desert serpent that has deadly, neurotoxic venom.

However, William Hayes, Professor of Biology in the Department of Earth and Biological Sciences at Loma Linda University, isn’t convinced. No one has scientifically demonstrated that snake venom or bite severity has changed in recent years—probably, Hayes suggested in a recent Book of Odds interview, because “we know that venom does not change appreciably within a few snake generations.”

There are far more plausible explanations for the observed snakebite trends in California. For one thing, the highly adaptable Southern Pacific rattlers are less likely to flee from development than other snakes; consequently, increasing human encroachment into their habitat may lead to more encounters and more bites. As for snakebite severity, Hayes suggests it probably has less do with the biter than with the bitten: “We also have to realize that changes are happening to general human health and in the treatment of snakebites,” he says. “There have been big increases in our society in asthma and obesity, which would predispose snakebite victims to more severe reactions.”

Southern California’s extended drought is another factor, decreasing snake reproduction and thus the number of small, juvenile snakes. This leaves larger, more dangerous snakes around to do the biting, and because large snakes inject more venom than small ones, their bites are more severe. However, the odds that a person in California will die from contact with a venomous snake or lizard in a year are still just 1 in 61,100,000.

Everywhere Else
Many areas have no poisonous snakes, but you can find rattlesnakes all over the country. The U.S. harbors fifteen species of them. Encounters are common, but attacks rare; according to Professor Walter E. Howard of the University of California, Davis, out of a total of just 1,000 rattlesnake bites a year, fewer than a dozen lead to death. The US Humane Society warns that the popularity of rattlesnake roundups is leading to the possible extinction of some species and points out that they play an important ecological role in controlling rodent populations.

Still, ophidiophobia (fear of snakes) isn’t likely to go away any time soon. The odds that an adult in the U.S. is afraid of snakes are 1 in 1.96 (51 percent), and the odds that an adult in the U.S. is very afraid of snakes are 1 in 2.78. This fear of slithering serpents may, in fact, be deeply rooted in our biology. Just like politics.

Originally published on Book of Odds

Photo courtesy of SearchNetMedia (cc)


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