Squirrels & Snakes & Venom: Oh My!
by Carole Brodsky, July 9, 2013
Nearly everyone in Mendocino County has encountered a rattlesnake. Though bites are rare, California's Northern Pacific Rattlesnake is worthy of healthy respect and is the subject of much misinformation.
Identifying the Pacific Rattlesnake is challenging, due to extreme color variations, location and age, according to Bob Keiffer, superintendent of the University of California Agriculture and Natural Resources at the Hopland Research and Extension Center. "There are even color variations as snakes mature. Some can be dark and hardly show any pattern. A few rare individuals develop long stripes," Keiffer explains.
"Another attribute unique to the mature Northern Pacific snake is their black and white striped tail, which looks very much like a king snake," says Keiffer. When trying to identify a rattlesnake, Keiffer suggests looking for the diamond pattern along the body and the large, diamond-shaped head surrounding the venom sacs.
Rattlesnakes mate in the spring, and around Aug. 1 to 25 young are live-born. By early October, they begin searching for a den site. Keiffer loosely tracks den sites at the center. "They look for winter den sites to hibernate- to shut down, slow down and retreat from harsh weather. It can be a small rock pile, but it needs a crack, rock crevice or other downward element going a foot or two into the ground." Multiple snakes often inhabit den sites. "Most of our sites have three to 20 snakes. In desert areas, there are massive sites containing 100 snakes," he continues.
Snakes detect the scent of other snakes to locate a den site. "Once they use a den site, they have a pattern in their brain and return. If one gets lost, a pile of plywood becomes a perfect, substitute den site." Keiffer urges people to use caution when moving stacks of wood or debris. "I've heard if you stack firewood, you will rarely find a snake underneath it, but unstacked piles offer more nooks and crannies for snakes to live in," he notes.
Mature females grow to about 60 centimeters in length, with males growing larger. "They'll get up to and over four feet long. I have seen a 56-inch long snake, and have heard rumors of a 60-inch snake, but I'm not believing that until I see it," he smiles.
For nearly 20 years, researchers at UC Davis have known some ground squirrel populations have developed significant amounts of immunity to rattlesnake venom. Recently, Matthew Holding, an Ohio State University graduate student came to the center to try and determine if co-evolution is creating unique interactions between predator and prey.
"The amount of ground squirrel resistance to rattlesnake venom varies from colony to colony and location to location," says Keiffer. Holding's theory is that venom immunity is relegated to specific squirrel populations and groups. "He's trying to tease out from genetic research why and how this has come about. It's like an arms race between squirrels and snakes. As rattlesnake toxin gets more potent, the ground squirrel population responds by building up immunity to the toxins," he continues.
Holding visited various sites throughout Northern California, collecting venom from rattlers and blood from squirrels, freezing samples in liquid nitrogen. "Matthew was gathering data from 20 snakes and 20 squirrels at each site to collect information for genetic analysis in the lab." His goal was to sample up to 25 populations spanning the northern two-thirds of California. No snakes or squirrels were harmed during the data collection process.
Holding's research underscores the fact that rattlesnake venom continues to intrigue scientists, doctors and veterinarians. Baby snakes are about six inches long at birth. Their primary diet consists of lizards. Juvenile snake venom contains higher amounts of neurotoxin, killing lizards quickly. "Young snakes bite lizards and hold onto them."
"Many vets and doctors aren't aware that Northern Pacific rattlesnakes don't reach maturity until they are about 60 centimeters long. At that magical size, snakes undergo a physical change. Their production of toxin in venom changes dramatically as they switch to a mammalian diet."
Mature snakes begin producing a venom much higher in hemotoxin and lower in neurotoxin. "It's the hemotoxin that breaks down muscle movement and blood cells in humans. They no longer grab prey and hold on. Mature snakes bite, inject and let go."
When snakes bite larger victims, usually in defense, they don't necessarily inject venom. "They have control, whether it's thinking or physiological control. It doesn't matter the snake's size or the age. Small and large snakes can bite with dry bites," says Keiffer.
Veterinarians generally provide antivenin to a bitten pet, but physicians often take a more cautious approach. "Many people have severe reactions to antivenin, so doctors monitor patients for swelling," Keiffer explains. Many people contract secondary infections from snakebites, so a course of antibiotics is almost always administered.
Though Keiffer is adamant that "no one should try this at home," venom could probably be swallowed. Eagles, Red-Tailed Hawks and even bass will kill and eat rattlesnakes with no deleterious effects. "With mammals, venom must be injected into the bloodstream - into the circulatory system of an animal," he continues.
"The rattle is for self-survival, not catching prey. It's used so larger critters don't step on them," says Keiffer. But rattlesnakes do not always herald their presence with their rattles. "I found a three-foot snake near one of our roads under a piece of tin. I didn't want someone to find it and kill it, so I scooped it up and carried it about 300 feet away. I did that three times in three weeks. It puffed up and hissed, but never rattled." Juveniles start out with a "button" rattle, accumulating additional segments over time. Rattles do not drop off when snakes shed their skin, about three times yearly.
"Be most careful when gardening and reaching down with your hands. Snakes crawl anywhere looking for food. They don't sweat. You will not find snakes in the hot sun. When it's cooler, they exit their dens and sit in the sun to warm up. They enjoy being on roads in the middle of summer nights. If they're run over during the day, it's probably where a tree has cast a shadow on the asphalt. No snake in the world will crawl on asphalt in the middle of the day."
Old ideas die hard, and Keiffer reminds the public never to "cut an X" over a snakebite and suck out the venom. "Keep the person calm, keep the bite area below the heart and apply something cool, but not as cold as an ice pack, over the wound."
Rattlesnakes are dangerous, but not aggressive or vicious. The classic display with coiled body and rattling tail is their defensive stance, and Keiffer notes that if given a chance to escape, they will do so rather than attack. "It's unfortunate to kill them. They control the rodent population. People hate mice and they hate rattlesnakes, but one can help keep the other population down," he concludes.
For more information on Hopland Research and Extension Center activities, visit: http://ucanr.org/sites/hopland/