Common names: ridge-nosed rattlesnake, Willard's rattlesnake, Willard's rattler.

Crotalus willardi is a venomous

Venomous snake

"Poisonous snake" redirects here. For true poisonous snakes, see Rhabdophis.Venomous snakes are snakes which have venom glands and specialized teeth for the injection of venom...

 pitviper

Crotalinae

The Crotalinae, commonly known as "pit vipers" or crotaline snakes, are a subfamily of venomous vipers found in Asia and the Americas. They are distinguished by the presence of a heat-sensing pit organ located between the eye and the nostril on either side of the head...

 species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 found in the southwestern United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 and Mexico

Mexico

The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...

. It is the most recent rattlesnake species to be discovered in the United States. Its specific name is in honor of its discoverer, Professor Frank C. Willard. Five subspecies

Subspecies

Subspecies in biological classification, is either a taxonomic rank subordinate to species, ora taxonomic unit in that rank . A subspecies cannot be recognized in isolation: a species will either be recognized as having no subspecies at all or two or more, never just one...

 are currently recognized, including the nominate subspecies described here. The Arizona ridge-nosed rattlesnake is the state reptile of Arizona.

Description

C. willardi is a rather small rattlesnake with all subspecies measuring one to two feet in length. Color patterns are generally a dark/brown base with pale or white horizontal striping, but vary slightly between subspecies. The distinctive ridges along each side of its nose, which are a series of upturned scales, are unique to its species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 and are the origin of its name.

Habitat

C. willardi is rarely found outside habitats of 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

This species is classified as Least Concern (LC) on the IUCN

World Conservation Union

The International Union for Conservation of Nature and Natural Resources is an international organization dedicated to finding "pragmatic solutions to our most pressing environment and development challenges." The organization publishes the IUCN Red List, compiling information from a network of...

 Red List of Threatened Species

IUCN Red List

The IUCN Red List of Threatened Species , founded in 1963, is the world's most comprehensive inventory of the global conservation status of biological species. The International Union for Conservation of Nature is the world's main authority on the conservation status of species...

 (v3.1, 2001). Species are listed as such due to their wide distribution, presumed large population, or because it is unlikely to be declining fast enough to qualify for listing in a more threatened category. The population trend is stable. Year assessed: 2007.

Although four of the five subspecies are secure, the New Mexico Ridge-nosed Rattlesnake (Crotalus willardi obscurus) is an endangered species

Endangered species

An endangered species is a population of organisms which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters...

 and listed as threatened by the U.S. Fish and Wildlife Service. Remaining populations are scattered throughout New Mexico, Arizona and the northern part of Mexico. Habitat destruction

Habitat destruction

Habitat destruction is the process in which natural habitat is rendered functionally unable to support the species present. In this process, the organisms that previously used the site are displaced or destroyed, reducing biodiversity. Habitat destruction by human activity mainly for the purpose of...

 is the cause of declining numbers but critical habitat designations (recovery measures) have been proposed.

Behavior

Rattlesnakes are primarily ambush hunters; they coil and lie waiting for prey to approach within striking distance. The diet of Crotalus willardi includes small mammals, lizards, birds, and large centipedes (Holycross et al. 2002). Young C. willardi feed primarily on large centipedes (Scolopendra sp.) and lizards, whereas adults feed primarily on mammals and birds (Holycross et al. 2002).

Like other rattlesnakes, C. willardi is ovoviviparous

Ovoviviparity

Ovoviviparity, ovovivipary, or ovivipary, is a mode of reproduction in animals in which embryos develop inside eggs that are retained within the mother's body until they are ready to hatch...

, meaning it gives birth and does not lay shelled 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

Gestation

Gestation is the carrying of an embryo or fetus inside a female viviparous animal. Mammals during pregnancy can have one or more gestations at the same time ....

 lasts approximately four to five months (Holycross and Goldberg 2001). Females give birth to two to nine (average 5) young in late July or August (Holycross and Goldberg 2001). Both sexes appear to reach reproductive maturity around 400 mm in body (snout to vent) length (Holycross and Goldberg 2001). Although captive snakes have reproduced annually, wild females probably reproduce every second or third year (Holycross and Goldberg 2001).

Venom

Due to the general size of the snake, venom discharge yields are low; thus, the largely hemotoxic

Hemotoxin

Hemotoxins, haemotoxins or hematotoxins are toxins that destroy red blood cells , disrupt blood clotting, and/or cause organ degeneration and generalized tissue damage. The term hemotoxin is to some degree a misnomer since toxins that damage the blood also damage other tissues...

 venom is not as potent as that of other rattlesnakes. There have been no documented deaths caused by Ridge-nosed rattlesnakes, but pain and discomfort can still result from a rare bite.

Subspecies

Subspecies	Taxon author	Common name	Geographic range
C. w. amabilis	Anderson, 1962	Del Nido ridge-nosed rattlesnake	Mexico Mexico The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...  in north-central Chihuahua.
C. w. meridionalis	Klauber Laurence Monroe Klauber Laurence M. Klauber , was an American herpetologist, and was considered to be the foremost authority on rattlesnakes... , 1949	Southern ridge-nosed rattlesnake	Mexico in southern Durango Durango Durango officially Estado Libre y Soberano de Durango is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. The state is located in Northwest Mexico. With a population of 1,632,934, it has Mexico's second-lowest population density, after Baja...  and southwestern Zacatecas Zacatecas Zacatecas officially Estado Libre y Soberano de Zacatecas is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is divided in 58 municipalities and its capital city is Zacatecas.... .
C. w. obscurus Crotalus willardi obscurus Crotalus willardi obscurus is a venomous pitviper subspecies found in northwestern Mexico and the southwestern United States.This is the only venomous snake listed as Threatened by the U.S. Fish and Wildlife Service.-Description:...	Harris & Simmons, 1974	Animas ridge-nosed rattlesnake	The United States United States The United States of America is a federal constitutional republic comprising fifty states and a federal district...  in extreme southeastern Arizona Arizona Arizona ; is a state located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix...  and extreme southwestern New Mexico New Mexico New Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S... . Mexico in extreme northwestern Chihuahua and extreme northeastern Sonora Sonora Sonora officially Estado Libre y Soberano de Sonora is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is divided into 72 municipalities; the capital city is Hermosillo.... .
C. w. silus	Klauber, 1949	Chihuahuan ridge-nosed rattlesnake	Mexico in western Chihuahua and eastern Sonora.
C. w. willardi	Meek Seth Eugene Meek Seth Eugene Meek was an American ichthyologist at the Field Museum of Natural History in Chicago. He was the first compiler of a book on Mexican freshwater fishes. Together with his assistant, Samuel F. Hildebrand, he produced the first book on the freshwater fishes of Panama.He often collaborated... , 1905	Arizona ridge-nosed rattlesnake	The United States in southeastern Arizona, and Mexico in northern Sonora.

External links

• Taxonomy of the New Mexican Ridge-nosed Rattlesnake at Virginia Tech. Accessed 12 December 2007.
• International Biopark: Ridge-nosed Rattelsnake at Biopark. Accessed 12 December 2007.
• US Fish & Wildlife Service Species Profile: Crotalus willardi at U.S. Fish & Wildlife Service. Accessed 12 December 2007.