Crotalus willardi

Common names: ridge-nosed rattlesnake, Willard's rattlesnake, Willard's rattler.^[2]

Crotalus willardi is a venomous pitviper species found in the southwestern United States and Mexico. 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.^[3] Five subspecies are currently recognized, including the nominate subspecies described here.^[4]

Additional recommended knowledge

Essential Laboratory Skills Guide

Daily Sensitivity Test

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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 genus 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 Red List of Threatened Species (v3.1, 2001).^[5] 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.^[6]

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

See also

• List of crotaline species and subspecies
• Crotalus by common name
• Crotalus by taxonomic synonyms
• Crotalinae by common name
• Crotalinae by taxonomic synonyms
• Snakebite

References

Further reading