Crotalus willardi

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Crotalus willardi
Arizona ridgenosed rattlesnake closeup.jpg
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Suborder: Serpentes
Family: Viperidae
Genus: Crotalus
C. willardi
Binomial name
Crotalus willardi
Meek, 1905
Crotalus willardi distribution.png
Synonyms [2] [3]
  • Crotalus willardi
    Meek, 1905
  • Crotalus willardi willardi
    Klauber, 1949
Common names: ridge-nosed rattlesnake, Willard's rattlesnake, Willard's rattler [4]

Crotalus willardi is a venomous pit viper species found in the southwestern United States and Mexico.

Venomous snakes are species of the suborder Serpentes that are capable of producing venom, which they use for killing prey, for defense, and to assist with digestion of their prey. The venom is typically delivered by injection using hollow or grooved fangs, although some venomous snakes lack well-developed fangs. Common venomous snakes include the families Elapidae, Viperidae, Atractaspididae, and some of the Colubridae. The toxicity of venom is mainly indicated by murine LD50, while multiple factors are considered to judge the potential danger to humans. Other important factors for risk assessment include the likelihood that a snake will bite, the quantity of venom delivered with the bite, the efficiency of the delivery mechanism, and the location of a bite on the body of the victim. Snake venom may have both neurotoxic and hemotoxic properties.

In biology, a species ( ) is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. Other ways of defining species include their karyotype, DNA sequence, morphology, behaviour or ecological niche. In addition, paleontologists use the concept of the chronospecies since fossil reproduction cannot be examined. While these definitions may seem adequate, when looked at more closely they represent problematic species concepts. For example, the boundaries between closely related species become unclear with hybridisation, in a species complex of hundreds of similar microspecies, and in a ring species. Also, among organisms that reproduce only asexually, the concept of a reproductive species breaks down, and each clone is potentially a microspecies.

United States Federal republic in North America

The United States of America (USA), commonly known as the United States or America, is a country comprising 50 states, a federal district, five major self-governing territories, and various possessions. At 3.8 million square miles, the United States is the world's third or fourth largest country by total area and is slightly smaller than the entire continent of Europe's 3.9 million square miles. With a population of over 327 million people, the U.S. is the third most populous country. The capital is Washington, D.C., and the largest city by population is New York City. Forty-eight states and the capital's federal district are contiguous in North America between Canada and Mexico. The State of Alaska is in the northwest corner of North America, bordered by Canada to the east and across the Bering Strait from Russia to the west. The State of Hawaii is an archipelago in the mid-Pacific Ocean. The U.S. territories are scattered about the Pacific Ocean and the Caribbean Sea, stretching across nine official time zones. The extremely diverse geography, climate, and wildlife of the United States make it one of the world's 17 megadiverse countries.



The specific name, willardi, is in honor of its discoverer, "Professor" Frank Cottle Willard, a businessman from Tombstone, Arizona. [5] [6]

In zoological nomenclature, the specific name is the second part within the scientific name of a species. The first part of the name of a species is the name of the genus or the generic name. The rules and regulations governing the giving of a new species name are explained in the article species description.


Originally described in 1905, Crotalus willardi is the most recent rattlesnake species to be discovered in the United States. Five subspecies are currently recognized, including the nominate subspecies, Crotalus willardi willardi, described here. [7] C. w. willardi is commonly known as the Arizona ridge-nosed rattlesnake, and is the state reptile of Arizona.

Subspecies taxonomic rank subordinate to species

In biological classification, the term subspecies refers to one of two or more populations of a species living in different subdivisions of the species' range and varying from one another by morphological characteristics. A single subspecies cannot be recognized independently: a species is either recognized as having no subspecies at all or at least two, including any that are extinct. The term is abbreviated subsp. in botany and bacteriology, ssp. in zoology. The plural is the same as the singular: subspecies.

Arizona state of the United States of America

Arizona is a state in the southwestern region of the United States. It is also part of the Western and the Mountain states. It is the sixth largest and the 14th most populous of the 50 states. Its capital and largest city is Phoenix. Arizona shares the Four Corners region with Utah, Colorado, and New Mexico; its other neighboring states are Nevada and California to the west and the Mexican states of Sonora and Baja California to the south and southwest.


Crotalus willardi is a rather small rattlesnake with all subspecies measuring one to two feet (30–60 cm) in length. Color patterns are generally a dark brown base with pale or white horizontal striping, but vary slightly among subspecies. The distinctive ridges along each side of its nose, which are a series of upturned scales, are unique to this species and are the origin of one of its common names, ridge-nosed rattlesnake.


C. willardi is rarely found outside habitats at high elevation. Wooded mountain ranges, primarily in the southwest, are where this reclusive species is found. Each subspecies’ range is limited to select mountain ranges, making human encounters rare events.

Conservation status

The species C. willardi is classified as Least Concern on the IUCN Red List of Threatened Species (v3.1, 2001). [1] Species are listed as such due to their wide distribution, presumed large population, or because they are unlikely to be declining fast enough to qualify for listing in a more threatened category. The population trend was stable when assessed in 2007. [8]

IUCN Red List inventory of the global conservation status of biological species

The IUCN Red List of Threatened Species, founded in 1965, has evolved to become the world's most comprehensive inventory of the global conservation status of biological species. It uses a set of criteria to evaluate the extinction risk of thousands of species and subspecies. These criteria are relevant to all species and all regions of the world. With its strong scientific base, the IUCN Red List is recognized as the most authoritative guide to the status of biological diversity. A series of Regional Red List are produced by countries or organizations, which assess the risk of extinction to species within a political management unit.

Although four of the five subspecies are secure, the New Mexico ridge-nosed rattlesnake (C. w. obscurus) is an endangered subspecies and listed as threatened by the US Fish and Wildlife Service. Remaining populations are scattered throughout New Mexico, Arizona and the northern part of Mexico. Habitat destruction is the cause of declining numbers, but critical habitat designations (recovery measures) have been proposed.

New Mexico State of the United States of America

New Mexico is a state in the Southwestern region of the United States of America; its capital and cultural center is Santa Fe, which was founded in 1610 as capital of Nuevo México, while its largest city is Albuquerque with its accompanying metropolitan area. It is one of the Mountain States and shares the Four Corners region with Utah, Colorado, and Arizona; its other neighboring states are Oklahoma to the northeast, Texas to the east-southeast, and the Mexican states of Chihuahua to the south and Sonora to the southwest. With a population around two million, New Mexico is the 36th state by population. With a total area of 121,592 sq mi (314,920 km2), it is the fifth-largest and sixth-least densely populated of the 50 states. Due to their geographic locations, northern and eastern New Mexico exhibit a colder, alpine climate, while western and southern New Mexico exhibit a warmer, arid climate.

Habitat destruction is the process by which natural habitat becomes incapable of supporting its native species. In this process, the organisms that previously used the site are displaced or destroyed reducing biodiversity. Habitat destruction by human activity is mainly for the purpose of harvesting natural resources for industrial production and urbanization. Clearing habitats for agriculture is the principal cause of habitat destruction. Other important causes of habitat destruction include mining, logging, trawling, and urban sprawl. Habitat destruction is currently ranked as the primary cause of species extinction worldwide. It is a process of natural environmental change that may be caused by habitat fragmentation, geological processes, climate change or by human activities such as the introduction of invasive species, ecosystem nutrient depletion, and other human activities.

Behavior and diet

Rattlesnakes are primarily ambush hunters; they coil and lie waiting for prey to approach within striking distance. The diet of C. willardi includes small mammals, lizards, birds, and large centipedes. The young feed primarily on large centipedes (Scolopendra spp.) and lizards, whereas adults feed primarily on mammals and birds. [9]


Like other rattlesnakes, C. willardi is ovoviviparous, meaning it gives birth and does not lay eggs. Contrasting with viviparous animals, the young still develop within an egg inside the female snake until their time of birth. Copulation occurs from late summer to early fall, and gestation lasts about four to five months. Females give birth to two to 9 (average five) young in late July or August. Both sexes appear to reach reproductive maturity around 400 mm (16 in) in body (snout to vent) length. Although captive snakes have reproduced annually, wild females probably reproduce every second or third year. [10]


Due to the generally small size of C. willardi, venom discharge yields are low; thus, the largely hemotoxic venom is not as life-threatening as that of other rattlesnakes. No documented deaths have been caused by ridge-nosed rattlesnakes, but pain and discomfort can still result from a rare bite.


Subspecies [7] Taxon author [7] Common name [11] Geographic range [12] [13]
C. w. amabilis Anderson, 1962Del Nido ridge-nosed rattlesnakeMexico in north-central Chihuahua
C. w. meridionalis Klauber, 1949Southern ridge-nosed rattlesnakeMexico in southern Durango and southwestern Zacatecas
C. w. obscurus Harris & Simmons, 1974New Mexico ridge-nosed rattlesnakeThe US in extreme southeastern Arizona and extreme southwestern New Mexico, Mexico in extreme northwestern Chihuahua and extreme northeastern Sonora
C. w. silus Klauber, 1949Chihuahuan ridge-nosed rattlesnakeWestern Chihuahua and eastern Sonora
C. w. willardi Meek, 1905Arizona ridge-nosed rattlesnakeSoutheastern Arizona, and northern Sonora

See also

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  5. Beltz, Ellin (2006). Biographies of People Honored in the Names of the Reptiles and Amphibians of North America
  6. Beolens, Bo; Watkins, Michael; Grayson, Michael (2011). The Eponym Dictionary of Reptiles. Baltimore: Johns Hopkins UNiversity Press. xiii + 296 pp. ISBN   978-1-4214-0135-5. (Crotalus willardi, p. 286).
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  8. 2001 Categories & Criteria (version 3.1) at the IUCN Red List . Accessed 13 September 2007.
  9. Holycross et al., 2002.
  10. Holycross & Goldberg, 2001.
  11. Mehrtens JM (1987). Living Snakes of the World in Color. New York: Sterling Publishers. 480 pp. ISBN   0-8069-6460-X.
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Further reading