After two decades of studying eastern diamondback rattlers, the author finds that America's deadliest snake is surprisingly timid
Kneeling motionless on the ground, I watched as a husky eastern diamondback rattlesnake slid from my 5-gallon can into its winter home, a dark gopher tortoise burrow.
"See you soon," I whispered, expecting to recapture this and eight other rattlesnakes I had recently caught, marked and released in the open pine forests of northern Florida.
But I did not see any of the snakes again until the following winter, when they had returned to their underground refuges to hibernate. My planned study of the life history of this widely feared but little-understood creature ended in failure because I couldn't find any of my subjects in the piney woods.
When I began my research in 1976, I was amazed at the dearth of scientific information on eastern diamondbacks. In the two decades since, I have learned why my first attempted study failed and, more important, I have filled in many details of the life history of the species. I have discovered that this creature, long despised by people, is highly evolved, incredibly complex and surprisingly gentle.
The eastern diamondback is the largest of the world's 32 species of rattlesnakes. Adults usually stretch 4 to 5 feet long and weigh from 4 to 8 pounds, but rare monsters more than 7 feet long and 15 pounds have been recorded. The distinct yellow and brown diamond patterns on its back give the snake its name. These rattlers are found in open-canopied pine forests throughout the southeastern United States, although their range and numbers are declining.
Like other rattlesnakes, the eastern diamondback's tail is tipped by a series of horny segments that rattle when shaken. And like its relatives, the eastern diamondback kills prey with venom injected through two fangs. Because of its large size and the potency of its venom, the eastern diamondback is the deadliest snake in the United States.
This latter fact, together with long-standing myths about rattlesnakes (see "Five Myths About Rattlesnakes" below), probably accounted for much of the ignorance about eastern diamondbacks I encountered when I began my studies in the mid-1970s. At the time, I had recently been hired as a research biologist at Tall Timbers Research Station, a nonprofit biological field station in northern Florida. To my dismay, the station managers allowed venomous snakes on the grounds to be killed, and I was determined to show them this policy was ill-advised. When my search of the scientific literature turned up little about the eastern diamondback, I realized I was situated perfectly to undertake the first long-term study of this species.
After my first attempt at recapturing the snakes failed, I decided to use radio transmitters. I made small cigar-shaped packages out of a transmitter and battery coated with beeswax, and gently pushed them down the throats of the snakes. (An adult eastern diamondback can hold a full-grown rabbit in its stomach, so the transmitters were not burdensome.) Radio tracking gave me the means to find my subject animals any time I wished--day or night.
With the help of the transmitters, I learned why I could not find the marked eastern diamondbacks in my first attempt. Their diamond-shaped color pattern blends well with dappled light and shadows, making it difficult to see against grass stems or dry leaves. But camouflage was only part of the answer. I also learned that the eastern diamondback, unlike its irascible cousin, the western diamondback, is a very placid animal that rarely moves or even rattles when approached by humans.
I have been bitten only once in the field (when I was attempting to catch a snake), despite hundreds of close encounters with eastern diamondbacks. Recently I performed a crude experiment to test how complacent the eastern diamondback is. I purposely stepped twice on a rattler coiled under a clump of muhley grass. When I tried to capture it, I was shocked to discover that under my other foot my weight had been bearing down on a second snake coiled under an adjacent muhley grass clump! During the episode, neither rattler moved nor rattled.
I believe there are two reasons why the eastern diamondback is reticent. First, the tendency to lie still and not rattle assists the rattlesnake in remaining camouflaged. Second, in the open pine forests of its native habitat, there are no places to escape from large predators. Rattling, which may have evolved to keep Pleistocene mammals from trampling rattlesnakes, became a distinct liability for eastern diamondbacks when people came on the scene. Native Americans would have been attracted to any rattling snake as an easy source of food, and eastern diamondback remains have been found in ancient Indian middens.
It is a good thing for humans that the eastern diamondback is so complacent. Because of its large size, it delivers a very large dose of venom. I know firsthand how potent the venom is. In 1976, I was bitten on the index finger by a small, three-foot-long snake. I felt no pain at first, but after four minutes my legs became paralyzed and I collapsed, unable to stand or walk. (Although most rattlesnakes have blood-attacking venom, the venom of the eastern diamondback is largely nerve-attacking, resulting in paralysis. Prey are quickly immobilized so they don't run far away and become difficult for the predator to locate.) I required 31 units of antivenin and a nine-day hospital stay to recover.
Relatively few people are bitten by snakes, however. Fewer than 10 people in the United States die each year from snake bites (about half of those fatalities are from eastern diamondback bites), but more than 100 die annually from either lightning strikes or bee and wasp stings. Most people who are bitten by snakes handle them regularly for fun or study.
In the course of my research, I have discovered many fascinating things about the eastern diamondback. For instance, the birthing season, August and September, is also the mating season. Females reach sexual maturity at three or four years of age and give birth every two or three years thereafter. Females store sperm for about seven months, after which the large ova are fertilized. Most nonvenomous snakes lay leathery eggs, but pit vipers such as the eastern diamondback give birth to live young. This gives the young protection in the body of the mother while they develop--unlike maturing in eggs buried in the soil, which are vulnerable to predators and the weather. An average brood consists of 14 baby eastern diamondbacks. At birth, newborns each average about 14 inches long. They have fully functional fangs and venom and are capable of eating a full-grown mouse.
Radiotelemetry has allowed me to study rattlesnake behavior at all hours. Many species of rattlesnakes are nocturnal, but my research showed that the eastern diamondback rarely moves after dark. I do not know what accounts for this difference between the eastern diamondback and its western relatives--perhaps it is simply because nocturnal rattlesnakes live in deserts where it is too hot for daytime activity.
I have also learned that the snakes feed entirely on warm-blooded prey, particularly small mammals such as rabbits, squirrels, rats and mice. Few birds have been found in their guts, possibly because after birds are struck, they fly off a short distance and do not leave a trail the snake can follow.
The eastern diamondback is an ambush predator that lies in hiding until a prey animal comes around. Rattlers find the best ambush locations by using a chemical sense that only reptiles possess. They identify the scent of their prey by tongue-flicking the ground. Scent particles picked up on the tongue-tips are placed forward into two small pouches on the roof of the mouth, a sensory organ called Jacobson's organ. The snake's ability to discriminate odors with its tongue and Jacobson's organ is probably better than our tongue and nose combined. (Male eastern diamondbacks can also perceive scent particles, or pheromones, emitted by the female at mating time.)
The snake tracks its prey and waits patiently until the creature is within striking range. The reptile quickly stabs the victim and injects venom with its fangs, then, after 5 to 30 minutes, the rattlesnake follows its prey using its tongue-tips to pick up the scent. Venom and fangs are thought to have evolved to procure the snake's meals, although they also help to protect snakes from the teeth of rodents and other mammal prey. Nonvenomous snakes, having only their mouths and tubular bodies with which to grasp prey, are often scarred from bites; they sometimes lose an eye or are even killed.
The native predators of the eastern diamondback are other snakes (eastern indigo, coachwhip, kingsnake, black racer), hawks and owls. But humans are a bigger problem than these predators. Shootings, road kills and "rattlesnake roundups" (mass hunting of rattlesnakes) have all taken their toll, but habitat loss and fragmentation are the major threats to this species. Development and agriculture have converted or destroyed more than 98 percent of the snake's preferred long-leaf pine habitat. As a consequence, the historic range of the eastern diamondback has shrunk dramatically. The species is now endangered in North Carolina and is probably extinct in Louisiana, states lying at the northern and western ends, respectively, of its range.
Why should we care about the fate of this venomous snake? Because it is a highly evolved life-form with complicated behaviors and unique attributes. Also, the species contributes to biodiversity and nutrient cycling in its ecosystem by eating mice, rats and rabbits.
The gentle-natured eastern diamondback and other rattlesnakes are good simply because they are. I, for one, hope we are wise enough to include rattlesnakes in our future.
D. Bruce Means is an ecologist and director of the Coastal Plains Institute and Land Conservancy, as well as adjunct professor at Florida State University in Tallahassee.
Five Myths About Rattlesnakes
Rattlesnakes pose a major threat to people.
Only six to ten people die each year from bites of all snake species in the United States--a small fraction of the number of people killed by lightning or by insects.
Rattlesnake oil, skin, vertebrae and organs cure toothaches, rheumatism, epilepsy and other ills.
There is no evidence that rattlesnake oil or body parts have medicinal value.
The snakes use their rattles to hypnotize prey.
Rattles likely evolved as signaling devices to keep large mammals from trampling the snakes.
The number of segments in a rattle equals the snake's age.
Rattlesnakes add a segment each time they shed, and young snakes may shed two to four times a year. Also, segments fall off as the snake ages.
Rattlesnakes swallow their young to protect them.
Rattlesnakes never swallow their young, but baby rattlers may emerge from the body of a mother that has been decapitated.