Rapid muscle twitching, as if a person had snakes crawling under the skin, is the telltale sign to Roy Johnson that the Southern Pacific rattlesnake has struck. On occasion, this symptom can progress to difficult breathing, coma and death. This snake's bite is one of the few to induce neurological symptoms, in contrast to most other rattlesnake bites, which initially produce swelling and bruising around the wound, notes Johnson, a physician in Palomar, Calif., who has treated some 700 snakebite cases. Increasingly, the proportion of rattlesnake bites in southern California are skewing to those like the more deadly Southern Pacific species, and scientists are not sure why.

Every year the Centers for Disease Control and Prevention logs 7,000 reports of snakebites in the U.S., which lead to about 15 deaths. Roughly 25 percent of the survivors incur some permanent damage. In southern California, reports from area hospitals and medical centers show a spike in serious bites the facilities say that, where they formerly saw patients with severe neurological symptoms once every two to three years, they now see several of these types of envenomations every year.

Johnson, for one, suspects that humans themselves are to blame for the increase. Most rattlesnakes warn off potential predators by shaking their noisy tails that is what the red rattlesnake and the speckled rattlesnake, southern California's other two dominant coastal species, tend to do. But the noise also makes the reptiles more likely to end up on the killing end of a shovel if the threat is human. In contrast, Southern Pacific rattlesnakes are more apt to lay low or move away than hiss and rattle when confronted, a strategy that may boost their chances of surviving, Johnson says. He speculates that by clubbing its competitors, humans have paved the way for the Southern Pacific to move into new areas. That animal "is adapting to human habitats much like the coyote whether we like it or not," John son remarks.

The rising incidence of supertoxic bite cases could also reflect a change in the species' venom. To predigest their prey, most rattlers produce so-called cytotoxins and hemotoxins, which damage tissue and disrupt blood clotting. But the Southern Pacific also produces a neurotoxin, which is more serious because it quickly affects breathing and muscle control. Anecdotal reports suggest that the snake's venom contains more neurotoxin than it did a few years ago. Richard Dart, director of the Rocky Mountain Poison and Drug Center in Denver, does not rule out that the species could have made its venom more toxic, perhaps by crossbreeding with the more deadly, desert-dwelling Mojave green rattlesnake or by turning on dormant genes developed over time in response to more resistant prey.

The amount of neurotoxin is indeed dramatic compared with the creature's close cousin, the Northern Pacific rattler. This species preys on ground and rock squirrels, which by six weeks of age develop a natural resistance to withstand a full envenomation, suggests research at the University of California, Davis. The Southern variety, however, has enough neurotoxin to overcome any such natural resistance, says biologist William Hayes of Loma Linda University. "Southern Pacifics have no problem getting lots of squirrels."

Still, Hayes does not believe that the rattler's venom has become more toxic. Rather he thinks that people are becoming less tolerant of snake venom, perhaps because of "pollution weakening human lungs and the immune system."

Sean Bush, a treating physician at Loma Linda University Medical Center, says that the Southern Pacific is definitely the "people-biting snake in California" and attributes the increase in incidents to humans encroaching on the animal's coastal and mountain habitat. We are, Bush says, "only now learning how potent and varied rattlesnake venom can be."

Editor's Note: This story was originally published with the title "Snakebit"

This article was originally published with the title Snakebit.

2 Comments

1. 1. bobbrew 07:51 AM 4/7/09

   I couldn't help but wonder why the author did not consider increased imigration traffic through rattlesnake habitat. That might explain most of the concerns he mentioned - increased pressure for meat, lung stress on those biten (TB), increased deaths.

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2. 2. BuckSkinMan 10:03 PM 8/15/09

   I do not see this increase in the number of bites by So. Pacific rattlers as too mysterious. For example, regardless of immigration from without our borders, Southern California has been for years a favorite "move to" place with people across the United States.
   
   With this more-or-less constant influx of people (who are by definition less likely to recognize the dangers of impinging on "rattlesnake country") it just makes mathematical sense that more people will be bitten by this species of rattlesnake.
   
   Also, the article mentions that Southern Pacific Rattlesnakes have always had more neurotoxin than the northern species (or is it subspecies?). Thus they are more able to get food - and thus multiply and expand their hunting territory.
   
   In Michigan there's only one poisonous snake: the Massassauga Rattlesnake (Sistrurus Catenatis). This is a small species, with an unusually small head and jaws. It's venom contains neurotoxin but the total volume of venom delivered is small. Thus, bites are rarely fatal. But here too, there are more people bitten in recent years. The most likely reason is reflected in the concentration of bite incidents: recently built suburban housing developments.
   
   City people move (in droves) to the suburbs, contractors build more houses, people and snakes cross paths more frequently (and city people are less wary and alert!). Result: more people being bitten by Massassauga rattlers.
   
   Probably coincidence: Massassaugas have tiny rattles which make little noise - and the snake is "retiring" and generally non-aggressive if not threatened. So they can be literally underfoot without being noticed: another condition contributing to the hazard. Much like the more dangerous Southern Pacific rattler.

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