Rattlesnakes of the United States and Canada

Rattlesnakes of the United States & Canada

Manny Rubio

ECO Herpetological Publishing & Distribution

A ground level view of an alert Green Prairie Rattlesnake, Crotalus v. viridis, clearly shows its facial pits, bifurcated tongue, prominent supraocular scales (above the eyes), and elliptical pupils.

TABLE OF CONTENTS

Introduction

Appreciating Rattlesnakes

Names

Rattlesnake Characteristics

Crotalus or Sistrurus

Rattle

Facial Pits

Eyesight

Nostrils

Tongue and Jacobson’s Organ

Fangs

The Strike

Offensive or Defensive Strike

Other Important Rattlesnake Characteristics

Characteristics Not Included in this Book

Additional Venomous Snakes

Harmless Mimics

Understanding Rattlesnake Natural History

Rattlesnakes as Efficient Predators

Caudal Luring

Feeding Strategies

Ambushing Prey: a Scenario

Ingesting Prey

Foraging

Rattlesnake Bite

Envenomation

Dry Bites

Rattlesnake Venom is a Complex, Destructive Cocktail

Ontogenetic Change in Venom

Precaution and Prevention

Treatment

Why a Medical Facility?

If You are Bitten

Recommended First Aid

Important Things Not to Do if Bitten

More Rattlesnake Natural History - Temperature and Survival

Seasonal Changes

Hibernation

Aestivation

Reproduction

Timber Rattlesnake Reproduction

Unique Reproduction

Habitat

Fragmentation & Destruction of Habitat

Food

Enemies

Interacting with Humans

Steeped in Religion

Rattlesnake Roundups

The Skin Trade

Exotic Pet Trade

Not Fear, Respect

To Prevent a Confrontation

Moving a Rattlesnake Safely: the Last Resort

In Closing - Thinking about keeping captive rattlesnakes? DON’T!

A Final Note

Species Accounts

Eastern Diamond-backed Rattlesnake, Crotalus adamanteus

Western Diamond-backed Rattlesnake, Crotalus atrox

Sidewinder, Crotalus cerastes

Mojave Desert Sidewinder, Crotalus cerastes cerastes

Sonoran Sidewinder, Crotalus cerastes cercobombus

Colorado Desert Sidewinder, Crotalus cerastes laterorepens

Arizona Black Rattlesnake, Crotalus cerberus

Timber Rattlesnake, Crotalus horridus

Rock Rattlesnake, Crotalus lepidus

Mottled Rock Rattlesnake, Crotalus lepidus lepidus

Banded Rock Rattlesnake, Crotalus lepidus klauberi

Speckled Rattlesnake, Crotalus mitchelli

Southwestern Speckled Rattlesnake, Crotalus mitchelli pyrrhus

Black-tailed Rattlesnake, Crotalus molossus

Northern Black-tailed Rattlesnake, Crotalus molossus molossus

Western Rattlesnake, Crotalus oreganus

Northern Pacific Rattlesnake, Crotalus oreganus oreganus

Grand Canyon Rattlesnake, Crotalus oreganus abyssus

Midget Faded Rattlesnake, Crotalus oreganus concolor

Southern Pacific Rattlesnake, Crotalus oreganus helleri

Great Basin Rattlesnake, Crotalus oreganus lutosus

Spotted Rattlesnake, Crotalus pricei

Twin-spotted Rattlesnake, Crotalus pricei pricei

Red Diamond Rattlesnake, Crotalus ruber

Red Diamond Rattlesnake, Crotalus ruber ruber

Mohave Rattlesnake, Crotalus scutulatus

Northern Mohave Rattlesnake, Crotalus scutulatus scutulatus

Panamint Rattlesnake, Crotalus stephensi

Tiger Rattlesnake, Crotalus tigris

Prairie Rattlesnake, Crotalus viridis

Green Prairie Rattlesnake, Crotalus viridis viridis

Hopi Rattlesnake, Crotalus viridis nuntius

Ridgenose Rattlesnake, Crotalus willardi

Arizona Ridgenose Rattlesnake, Crotalus willardi willardi

New Mexico Ridgenose Rattlesnake, Crotalus willardi obscurus

Massasauga, Sistrurus catenatus

Eastern Massasauga, Sistrurus catenatus catenatus

Desert Massasauga, Sistrurus catenatus tergeminus

Western Massasauga, Sistrurus catenatus edwardsi

Pygmy Rattlesnake, Sistrurus miliarius

Carolina Pygmy Rattlesnake, Sistrurus miliarius miliarius

Dusky Pygmy Rattlesnake, Sistrurus miliarius barbouri

Western Pygmy Rattlesnake, Sistrurus miliarius streckeri

Two confusing species - A Comparison of C. atrox & C. s. scutulatus

Appendices

Selected References

Herpetological Organizations

Internet

References

Glossary

Range Maps

Acknowledgements

How to Use this Book

About the Author

Copyright

INTRODUCTION

Throughout the world humans have always treated snakes with awe, reverence, respect, or fear. Many cultures endow them with mystical, supernatural powers, as messengers to gods and as divine beings. Their ability to cause great pain, or kill with an efficient, complicated injection apparatus, places venomous snakes on a higher plane than other snakes. The Western Hemisphere is graced with the pinnacle of venomous snake sophistication--- rattlesnakes! Not only is their ability to envenomate extremely effective, they have a rattle to warn potential predators of this special capability. In the grand scheme of snake evolution, scientists consider them highly advanced.

Rattlesnakes are wonderfully adapted creatures and deserving of all the positive adjectives bestowed upon them. When viewed objectively, they are magnificent-- in color, pattern, shape, and ability to live in what humans consider a diversity of hostile environments.

My fascination with rattlesnakes goes back a half century, when I was fortunate to live my teen years near the Staten Island Zoo. At that time, this small zoo was renowned for having the largest and most diversified collection of rattlesnakes in the world. The collection was amassed by the legendary herpetologist, Carl Kauffeld, and maintained almost exclusively by reptile keeper Carl Alimonti. I was so enthralled, I would visit the zoo whenever possible to talk rattlesnakes with the staff. Weekends were spent as a volunteer in the reptile wing, where I worked with non-venomous reptiles and observed (but not handled) rattlesnakes. Kauffeld nurtured my interest, eventually becoming a friend and mentor.

In college I pursued a degree in biology, but chose a profession as an editorial/commercial photographer, keeping the study of amphibians and reptiles a primary avocation. My career enabled travel throughout the New World where I photographed, collected, and occasionally brought back needed rattlesnake species for the zoo. In an ongoing quest to learn more, countless hours have been spent gathering and reading pertinent literature, and studying and writing about all phases of rattlesnakes’ behavior and natural history.

The allure continues. Although I rarely collect, I enjoy going into the field in pursuit of rare Latin American species that have evaded me. I have had thousands of encounters with rattlesnakes, but nothing gets the ole heart pumpin’ faster than an aroused adult Eastern Diamond-backed Rattlesnake. Its massive head, poised atop a striking coil, tongue-flicking long and laboriously, and its rattles rattling furiously, while it attempts to back away, totally aware of my every move and ready to respond to any intrusion on its space with a lightning fast strike.

The thrill of confronting an Eastern Diamond-backed Rattlesnake, C. adamanteus.

Since the publication of my book Rattlesnake: Portrait of a Predator in 1998, considerable research has been done on the classification and relationships of the once 83 forms of rattlesnakes. With the new millennium, molecular biology (most specifically, analysis of mitochondrial DNA) has emerged as a method of hypothesizing evolutionary derivations and linkages among closely related living things. Molecular biologists have recently proposed PhyloCode as the name of this classification system. It entails using DNA as the process of redefining the taxonomy of all plants and animals, and would replace the long standing (250+ years) Linnaean system. The plan is controversial, and widely debated. Scientists are concerned that time and precious funding are better spent describing new species before they become extinct, rather than laboriously reassigning those that have been categorized. Many young biologists find it a relatively simple method of making judgments and publishing papers without ever having seen live rattlesnakes, much less observing them in the field.

This book presents the current classification of North American rattlesnakes north of Mexico. The region was limited because the majority of DNA studies have been done on rattlesnakes from the United States with supporting data published in peer reviewed journals. Acceptance of scientific names (taxonomic classification) can take years to reach consensus, so I have included the newer assigned names, while noting the previous ones in some cases. Naturalists, with more than a casual interest, should find this helpful in understanding the changes. Funding for research and accessibility to specimens from Latin America are muddled in politics and priorities. Eventually, DNA samples from the needed snakes will be acquired, and analysis will be undertaken. No doubt this will take several years, with acceptance or refutation of the results taking additional years.

Each of the 30 species and subspecies of rattlesnakes found in the United States and Canada are described with accompanying photographs and range maps. Information on rattlesnake natural history is included to better understand their habitat preferences, relationships with other animals, and to help accurately identify them.

The intent of this book is to show rattlesnakes as the amazing, unique animals they are. Television, the internet, magazines, science museums, nature centers, and wildlife organizations are nurturing a growing interest in the wonders of our natural world. People are accepting the importance of every animal and plant in the elaborate, convoluted web of living things.

Unfortunately, some of what is being presented on television is misinformation, or a distortion to make it more dramatic, exciting, and maintain higher ratings. Information available on the internet is frequently unreliable. It is almost always unedited and conjecture.

The extraordinary interest in reptiles is confirmed by an estimated two million people who keep them as pets in the United States. Sadly, it has become an issue in many states and provinces where politicians, hungry for publicity, make absurd comments and attempts to regulate exotic animals. Unfortunately, the media have exacerbated the situation by disseminating stories wrought with unfounded information, statistics, and supposition. This has fueled growing disapproval and misunderstanding to such a degree that it is difficult for most people to envision snakes as anything but an enemy. Moreover, many are being wheedled into believing that all snakes are dangerous, menacing, and should be killed on sight. No rattlesnakes are aggressive, rather they are shy, retiring, and prefer to avoid a confrontation by escaping. When pressed, they bite in self-defense, as a last resort.

Ophidiophobia (fear of snakes) is one of the more complicated and difficult fears to overcome. Psychologists estimate that more than half of the American population demonstrates uneasiness with snakes; a fifth are terrified by them. Most apprehension and misunderstanding is based in religion. It requires considerable understanding to demonstrate the importance of snakes, and that they suffer baseless, overzealous persecution. It is vital that we view ourselves as trespassers and snakes as an established part of the ecosystem long before we intruded.

Make no mistake; the future of our natural environment lies in our hands.

Look and you will see.

Read and you will learn.

Think and you will know.

To get the most value from this book it is important to understand a few principles relating to its contents.

Natural science is not a staid discipline, it is constantly changing. As molecular biology and biochemistry advance, investigative techniques become more refined, and as formally inaccessible regions are explored, new and additional information is divulged and changes are made.

Physical characteristics of plants and animals vary, sometimes widely, within a designated species. It is ill-advised to be overly precise and firm by making conclusions, invariably they will be changed. Modifiers have been used extensively to avoid giving the impression that everything is cast in stone. In most places this was done to make qualified generalizations. The reader must be aware of variations in rattlesnake characteristics; they may be extensive. Individuals from unknown locals are difficult for all except the most astute naturalists to tell apart; and then the identification may be considered inconclusive. Pattern and coloration are not enough to be definitive. The dilemma is compounded by individuals from zones of intergradation or hybridization, and normal variation within species.

The medical advice presented is the most recent, but the author is not a medical doctor. It is offered as information, and the author will not assume any responsibility for the actions taken by the reader.

Because we are dealing with a potentially life-threatening situation, if there is any doubt, be conservative. Avoid a conflict and/or taking any unnecessary chances when dealing with a venomous animal.

Hopefully the reader will be stimulated to learn more about rattlesnakes. Most of the material in Suggested Reading is available in larger libraries or from the publishers, and is a good place to start. These books have bibliographies which offer additional sources.

APPRECIATING

RATTLESNAKES

The tongue of this wary Western Diamondback Rattlesnake, C atrox, picks microscopic particles from the air in reaction to the closeness of the photographer.

NAMES

Identifying a rattlesnake, indeed any animal, has been an ongoing dilemma because the same form is known by a variety of common names throughout its range. The mess is compounded greatly when the animal is widely distributed over many states, hundreds of miles and countries with different languages and dialects.

The American Ornithological Society has made great strides by standardizing and accepting a single common name for a given bird species. Arachnologists and some herpetologists are attempting similar naming strategies, but wide acceptance is slow in being achieved and will always vary with countries with differing languages.

[I have chosen to follow the lead of The American Ornithological Society by including common names as proper names and have capitalized them. The choice of common names follows Crother (2008)]

During the early years of natural history discovery, it was apparent that some form of standardization and organization was needed to avoid an otherwise overwhelming predicament. In 1735 Swedish plant biologist Karl von Linneaus implemented a binomial (two name) system of naming a particular plant or animal—genus and species. To better differentiate forms, the Linnean system was expanded into another category, subspecies, making it a trinomial. In many cases, no subspecies have been identified; they are recognized as being monotypic. This places a plant or animal in an exact position within a hierarchal system. The combination is commonly referred to as its scientific name. Knowledgeable naturalists utilize the scientific name rather than the common name when relating to a life form.

Charles Darwin theorized evolution in 1859. Using similarities and differences of physical features, groupings of plants and animals were eventually separated and aligned in an encompassing, but theoretical evolutionary tree. Following the tree toward its root, each form is classified into wider categories: family, order, class, phylum, kingdom, and domain. With further sophisticated study, affinities are re-described and organisms are re-assigned, or new ones are named. PhyloCode (using molecular biology) is proposed to replace the Linnean system.

RATTLESNAKE CHARACTERISTICS

As we will see, two distinctive characteristics identify a rattlesnake—the rattle and the facial pits. (NOTE: Remember that the rattle may be broken off or merely a button if a newborn.)

Crotalus or Sistrurus?

In our region rattlesnakes are divided into two genera (major taxonomic groups) because they exhibit minor, but important, anatomical differences which disclose that they evolved along slightly divergent paths. These physical characters make distinguishing them uncomplicated and easy.

Crotalus is comprised of the greatest number and most widely differing-sized species. They range from the largest forms (e.g., Eastern Diamond-backed Rattlesnakes) to the smallest, montane ones (e.g., Twin-spotted Rattlesnakes). Sistrurus has much fewer forms, and they are generally smaller in size (Pygmy Rattlesnakes and Massasaugas).

In the United States and Canada, when the scales on the rattlesnake’s crown are mostly the same size and shape, the snake is Crotalus. If they are clearly defined as nine large, mostly paired scales, the snake is Sistrurus. For many years Mexican rattlesnakes with the latter head scale structure were considered to be Sistrurus, but recently they have been reassigned as Crotalus. It is quite possible that the unique head scalation will eventually lead to them being assigned as another genus.

There is a recent controversial paper with a completely revised taxonomy of all rattlesnakes (Hoser, R. 2009.). It divides rattlesnakes into five genera and seven sub-genera and needs considerable study by crotalid specialists to decide its efficacy.

Head Scale Differences in Sistrurus & Crotalus

Dusky Pygmy Rattlesnake

Sistrurus miliarius barbouri

Northern Mohave Rattlesnake

Crotalus scutulatus scutulatus

RATTLE

In reviewing many theories on the use of the rattle, consensus is that it exists to warn potential predators and larger animals of the snake’s presence, and that they may be too close.

With the exception of newborns, all normal rattlesnakes north of Mexico have a blunt tail that ends in a rattle. Newborns have a cartilaginous, rounded tail tip that begins to form a rattle when they shed their skin. As they grow, they shed the complete outer skin except for the thicker, modified tail tip; it remains attached to the snake as a loosely interlocking segment to the rattle.

Rattle of a Northern Pacific Rattlesnake, C. o. oreganus, complete with the first segment. The inset is a cross section model showing the interlocking segments.

By the end of the first full year, the snakes have fed, grown, and undergone two to five sheds, depending upon their increase in size. Each shed leaves them another tapered segment. The accumulated segments are called a string, and give them the ability to produce the signature sound. Additional segments are added with each subsequent shedding for the rest of their lives. After reaching maturity, growth slows considerably, and they may shed only once or twice annually.

After a few years, with the buildup of a dozen or more segments, the rattle becomes lengthy and fragile. Wear, from rubbing against countless objects during the snake’s normal activities, weakens the oldest segments, and they crack, break, and fall off. It is common to find a large adult individual with a short, non-tapering rattle.

Although rare, a rattlesnake may have the end of its tail damaged or deformed at birth to the point of being unable to produce the segments of a rattle. There is one rattlesnake species inhabiting the small Mexican island, Isla Catalina, in the Sea of Cortez, that is incapable of developing interlocking segments and subsequently has no rattle. At least one other island form appears to be undergoing a similar change as new generations develop.

FACIAL PITS

The head reveals a deep, scoop-shaped indentation on each side between the eyes and nostrils-- the facial pit. These are unique, heat sensing structures that enable rattlesnakes to see heat radiating from an object.

From head on, the pits provide a thermal view of potential prey, regardless of minor obstacles like grass. The pits detect infrared (heat) being transmitted from the prey animal’s body to judge its distance. Heat is captured by a network