In recent years, some doctors and toxicologists in Southern California and across the Southwest have reported anecdotal evidence of an increase in snakebite cases, with more patients suffering extreme – sometimes fatal – consequences.
Last summer, San Diego Poison Control officials said the recorded number of “unusually powerful” snakebites had increased for the second consecutive year. Media attention has fanned the furor, most recently an article in the current issue of Scientific American that suggests the venom of the southern Pacific rattlesnake, a common species in San Diego County, is becoming “extratoxic.”
That’s bad news for potential bite victims and arguably worse news for rattlesnakes, but some herpetologists and snake experts question whether the phenomenon is real.
Each year, the San Diego division of the California Poison Control System records 40 to 60 rattlesnake bites in San Diego County, said Dr. Richard Clark, a toxicologist at the University of California San Diego and medical director of the local poison control center. In 2004, the poison control system recorded 42 rattlesnake bites to humans in the county. In 2005, there were 45; in 2006, 54; in 2007, 47; and last year, 41.
The real number is higher, Clark said, because snakebites are not among cases that doctors are required to report. Clark said he believes that locally, one or two snakebites in 2008 were fatal.
In the United States, according to the Centers for Disease Control and Prevention, there are roughly 7,000 reported venomous snakebites each year, 15 of which on average prove fatal.
Clark said the number of snakebites varies with shifting environmental conditions. Wildfires, for example, can substantially affect rattlesnake habitat, reproduction rates and prey availability. He predicted that the annual number of rattlesnake bites will trend upward “as we continue to build and expand into East County and snake habitat.”
San Diego County is home to four species of rattlesnake: the speckled, the red diamond, the sidewinder and the southern Pacific, which is a subspecies of the western rattlesnake and the most abundant rattler in the region.
It’s the southern Pacific rattlesnake that’s generating headlines and concern, with speculation that the species is evolving and expanding into a more dangerous animal. To some degree, scientists say, there are reasons to worry.
First, southern Pacifics are more widely distributed than other indigenous rattlesnakes. They live in diverse habitat from the beaches to the mountains, and they are tolerant of disturbed, developed areas.
“Southern Pacific rattlesnakes thrive where people prefer to live, so people encounter them relatively frequently,” said Dr. Sean Bush, a professor of emergency medicine at Loma Linda University and a snake researcher.
Second, the snakes appear to be more easily annoyed than other species and are more likely to defend themselves aggressively. Clark described them as having “nasty dispositions” and more inclined than other rattlers to bite before retreat.
Bush called them “people-biting snakes.”
It’s the bite, of course, that concerns doctors, scientists and potential victims. Rattlesnake venom is a lethal cocktail of toxins that quickly causes significant tissue damage and hemorrhaging. The bitten prey weakens and dies, and then the snake consumes it.
In humans, an ordinary rattlesnake bite produces initial swelling and bruising around the wound, but quick treatment and new antivenins mean rattlesnake bites are rarely fatal.
There is research to indicate that the venom of at least some southern Pacific rattlesnakes contains an additional deadly ingredient: a fast-acting neurotoxin that affects breathing and muscle control. (A telling symptom of a southern Pacific bite is rapid, uncontrollable muscle twitching.)
A neurotoxin is also present in the Mohave rattlesnake, a deadlier, desert-dwelling species found primarily in Arizona and Mexico, though part of its range reaches into eastern San Diego County.
Some researchers have speculated that interbreeding with Mohave rattlesnakes has produced a deadlier version of the southern Pacific. Richard Dart, director of the Rocky Mountain Poison and Drug Center in Denver, said it’s possible. “If they’re rattlesnakes, they’ll interbreed. I’ve seen it in the lab, though it’s probably not something that happens in nature every mating season.”
William Hayes, a biologist and snake researcher at Loma Linda University, is more skeptical. He dismisses the idea that southern Pacific rattlesnakes are naturally evolving a more toxic venom. The majority of western rattlesnakes lack neurotoxins in their venom, he said. If some southern Pacific rattlesnakes do in fact have them, it’s likely to be an unidentified toxin.
Bush suggests the phenomenon may be an example of convergent evolution.
“That is, an animal develops a similar trait because it utilizes it for a similar task,” Bush said. “Sort of like giraffes and brontosauruses both having long necks, probably to feed on leaves high in trees.”
On one thing all of the researchers agree: Size matters in snakebites. Adult victims tend to fare better than children because of greater body mass. And the bigger the snake, the worse its bite.
“I don’t know where the myth about baby rattlers being more dangerous came from,” said Dr. Roy Johnson, an Escondido-based physician and herpetologist. “The key is how much venom is injected, and a big snake injects a lot more venom than a small snake.”
Anecdotal reports of nastier snakebites may be due to a proportionate increase in big snakes. Hayes said chronic drought conditions in Southern California may have reduced reproductive rates among rodents and other small mammals, which are the southern Pacific’s preferred prey.
As a result, the rattlesnake’s reproductive rate has also declined, reducing the number of juvenile snakes. “We may well be seeing a shift toward more bites being inflicted by larger rattlesnakes simply because smaller snakes may now be disproportionately few,” Hayes said. Southern Pacific rattlesnakes can grow up to 4 feet in length.
Snakebite data suggest big snakes usually bite big people. Children tend to be bitten by small rattlesnakes they stumble upon inadvertently. Adults are more often bitten by rattlesnakes they try to pick up.
“If anything, we can expect the escalating emphasis on snakes in nature television programming to inspire more people to make dumb decisions about handling venomous snakes,” Hayes said. “We might be seeing a shift in the demography of snakebite victims, with more adult men, many under the influence of alcohol, getting bitten by snakes they should not have been messing with.”
Johnson, the Escondido physician who has treated hundreds of snakebite victims over 30 years, agreed: “Mostly people get bitten because they tried picking up a snake, because they weren’t smart enough to know better.”
Rattlesnake bites are rarely fatal when the victim receives fast treatment. Administering antivenin is critical. Traditional first aid, such as applying ice, using a tourniquet or putting suction to the wound, may cause more harm than good.
If the bite occurs while in a remote setting, the wounded area should be immobilized (especially if it is an arm or leg) and the victim quickly but safely transported to the nearest phone. Dial 911 and wait for assistance. If no phone is available, drive to a hospital or clinic.
LOCAL RATTLESNAKES
WESTERN/SOUTHERN PACIFIC
Crotalus viridis helleri
Description: Up to 4 feet in length. Light gray or brown, with pale margins around dorsal blotches. At higher elevations, specimens may be black. Juveniles have yellow-green tails.
Habitat: Seacoast to pine-wooded mountain ranges.
Behavior: Aggressively defensive.
RED DIAMOND
Crotalus ruber
Description: Usually in the 3-foot range, though some adults may exceed 5 feet. Distinctively reddish or tan, with subtle diamond pattern on back and a black-and-white tail.
Habitat: Areas of rock and brush, such as coastal sage scrub.
Behavior: Generally docile, though individual temperaments vary.
SOUTHWESTERN SPECKLED
Crotalus mitchelli pyrrhus
Description: Up to 3 feet in length. Color matches earth tones of environs, with black speckles forming indistinct bars or blotches on back. Dark rings on tail.
Habitat: Most abundant in inland rocky areas and in the desert.
Behavior: Alert, nervous and quick to rattle when disturbed.
SIDEWINDER
Crotalus cerastes
Description: Rarely exceeds 2 feet. Generally pale tan and pink, matching desert sands. Dark square blotches on backside. Hornlike protrusions above eyes.
Habitat: Sandy desert
Behavior: Quick and elusive, leaving distinctive J-shaped tracks.
Remember LETHAL? It’s an app that can keep you awake at night by telling you about all of the dangerous things that can kill, maim, or at least injure you. The good thing is that LETHAL does it in a humorous way.