B.C. Reptiles & Amphibians

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Credit: Andrew Nydam

Western Rattlesnake

Crotalus oreganus

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Description

Other names: Northern Pacific Rattlesnake; Crotalus oreganus oreganus

Previously referred to as: Crotalus viridis oreganus

The Western Rattlesnake is a member of the Viper family and the only truly venomous species found in British Columbia. They can be differentiated from the other snake species in British Columbia by 3 main features; a rattle on the end of its tail, a distinct, skinny neck, and a broad, triangular head. They are a medium-sized snake, with adults ranging from 60 cm to 1.2 m, with females generally being smaller than males. They have heavily keeled scales giving them a rough texture and appearance, with dark blotches surrounded by light halos running down their backs contrasted against a tan, olive, brown, or dark green background that transitions to alternating black and white rings at the tail. Colouration is brightest in juveniles and becomes dull and faded as individuals age. The head is broad and triangular, with large eyes and vertical pupils, and deep pits between the nostrils and eyes that are used to sense heat. Neonatal animals are venomous at birth but lack a developed rattle. Newborn rattlesnakes will have a single modified scale at the tip of tail called a button. Each time a rattlesnake sheds its skin, a new piece of hardened skin is added to the tail below the button, elongating the rattle. With each shed the rattle grows larger, increasing the intensity of the sound.

Listen to the Indigenous words for “rattlesnake” here!

Click below to hear the sound of a
rattlesnake shaking its rattle!

Click below to hear the sound of a
rattlesnake shaking its rattle!

Similar Species

The Western Rattlesnake is the only species of rattlesnake in British Columbia, but there are other blotched species that may resemble them, like the Great Basin Gophersnake or the Desert Nightsnake. Neither of these other species has a rattle, nor are they venomous. The Gophersnake has a much smaller, skinnier head, eyes with round pupils, and a skinny tail that tapers to a fine point. Desert Nightsnakes are very rare in British Columbia and are considerably smaller than Western Rattlesnakes, with a small, skinny head.

Western Rattlesnake

Great Basin Gophersnake

Desert Nightsnake

Habitat

Western Rattlesnakes hibernate throughout the winter in underground hibernacula that they share with other Western Rattlesnakes, and sometimes other snake species such as Great Basin Gophersnakes, Western Yellow-bellied Racers, and Common and Western Terrestrial Gartersnakes. They have a high fidelity to their hibernacula and return to the same sites every year. When temperatures rise in the spring, they emerge from their dens and make migrations to summer hunting grounds. Pregnant females on the other hand, typically stay very close to the hibernacula, basking on south-facing slopes that provide heat and shelter for the developing embryos they carry. Rattlesnake hibernacula are typically located on south-facing cliffs with rocky outcrops or talus. During the summer, rattlesnakes are generally found in the more productive valley bottoms and adjacent slopes where they hunt. Western Rattlesnakes may migrate several kilometers between their summer foraging grounds and their overwintering dens. In British Columbia, Western Rattlesnakes are associated with arid grasslands and sagebrush shrub-steppe. During the hottest parts of the summer, rattlesnakes are generally nocturnal and may even venture into cooler, high-elevation forested habitats.

Reproduction

Western Rattlesnakes, unlike most of the other snakes in British Columbia, do not mate in the spring, but rather in the late summer or early fall. Females that have sufficient fat reserves and are ready to reproduce will leave an ‘odour trail’ as they move about the habitat that males will seek out and follow. After mating, the female will carry the sperm overwinter, not allowing the eggs to be fertilized yet. In the following spring if she has maintained adequate fat reserves to have a successful pregnancy, the eggs will then be fertilized. During the pregnancy females have a very reduced appetite, and provide most of their fat reserves to the developing embryos. Western Rattlesnakes are ovoviviparous, and when 2-8 live young are born in the autumn, the females haven’t eaten for nearly an entire year and are very skinny. The following summer (or sometimes two summers) are spent feeding and regaining body mass to acquire enough fat reserves to reproduce again. Larger, fatter females will have larger litters than smaller, skinnier individuals. Females don’t reach sexual maturity until 4-7 years of age, depending on their fat reserves, and will reproduce every 1-3 years. Males reach sexual maturity as early as 3 years of age, however, breeding females are limited in any given year and males will aggressively compete for breeding rights, with the largest males usually emerging victorious from such confrontations. Western Rattlesnakes may live up to 30 years.

Diet

Western Rattlesnakes are passive predators, specializing in ambush hunting. They will generally coil themselves in a position where their camouflage helps conceal them, sitting silently, waiting for prey to cross their path. Their necks will kink into an “S” shape that acts like a compressed spring to allow for a blindingly fast strike should their prey enter the strike zone. In the blink of an eye, the rattlesnake strikes their prey, injecting venom through long, hollow fangs. Rattlesnakes typically do not hold onto their prey, and the venom does not usually kill their prey right away. Instead, rattlesnakes will follow the scent of the injured prey to wherever they run off to, and will swallow them whole once the immobilized prey is located. The venom of the Western Rattlesnake is a hemotoxin, a toxin that targets and destroys red blood cells, which begins digesting the tissues of their prey from the inside out, while also immobilizing the nervous system.

Western Rattlesnakes mainly eat small mammals like mice, voles, chipmunks, and squirrels. However, larger rattlesnakes may be able to take larger or more complex prey like marmots, rabbits, or birds. Juveniles are limited by their size in what they can eat, and mainly hunt shrews and nestling mice and voles.

Conservation Status

Global: G5 (2016)

COSEWIC: T

SARA:1-T (2005)

Provincial: S2S3 (2018)

BC List: Blue

Learn more about conservation status rankings here

Threats

Western Rattlesnakes are restricted to a small number of valleys in British Columbia where their habitat is being rapidly converted into urban and agricultural landscapes. Thus, the survival of Western Rattlesnakes in British Columbia is dependent on the preservation of their habitat. Development that includes rock removal or blasting can destroy an entire population if it impacts even a single hibernaculum. Road mortality is an increasing concern for the persistence of Western Rattlesnakes, especially where roads bisect the migration routes between summer and overwintering habitat. Sadly, human persecution from fearful and misinformed humans continues to threaten rattlesnakes, despite their protected status. Furthermore, the abundance of shrews may be important for the recruitment of rattlesnakes, as they are a major prey item for juvenile rattlesnakes.
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What to do if you encounter a rattlesnake?

If you hear or see a rattlesnake, stop immediately! Locate the snake or where the sound of the snake is coming from. If you are close to the snake (within 1 m) remain still and allow the snake to calm down and back away. Look around the area as there may be other snakes nearby. Once you are more than one snake body length away (>1 m), create space, and go around the snake giving it a wide berth. Western Rattlesnakes are generally quite docile, and would prefer to avoid a conflict than strike at a potential threat. Western Rattlesnakes will never pursue people to attack, and will instead retreat and find a place to hide. Furthermore, all snakes, including Western Rattlesnakes, are protected under B.C.’s Wildlife Act, making it illegal to kill or harm them, or remove them from the wild. If you do encounter a dead snake, don’t touch it. The biting reflex can remain intact for quite some time after death.

The Danger of the Rattlesnake Bite

Most people fear and/or persecute rattlesnakes because they are a venomous species. Western Rattlesnakes certainly deserve respect and should never be handled. However, fatalities from Western Rattlesnake bites are extremely rare; in fact, insects kill more people in North America every year than snakes. In the event of a bite the most important thing is to remain calm and arrange transport to a medical facility as soon as possible. Bites will normally present themselves as two small puncture holes side-by-side from the two fangs. Do not attempt any medical intervention yourself, and await treatment from a medical professional.

The best way to prevent a rattlesnake bite is by being prepared and aware of your surroundings. Rattlesnake bites can easily be avoided by staying on trails and being aware of where you place your hands and feet. If you know you are venturing into rattlesnake habitat, make sure to wear closed-toe shoes and long pants; even light pants have been shown to reduce the amount of venom a snake may inject if bitten on the leg. The most important thing to remember is that these are timid animals; with common sense and precaution we can minimize danger to both humans and snakes.

Another common myth is that young rattlesnakes are more dangerous than adults. Young rattlesnakes possess full toxicity venom from birth, but have much less volume than an adult. Although juvenile snakes may inject less venom than larger individuals, anyone bitten by a rattlesnake of any size should seek immediate medical attention.
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Did You Know?

Contrary to popular belief, the Western Rattlesnake is generally a quiet, non-aggressive snake that prefers to avoid conflict. The primary defense strategy of Western Rattlesnakes is not to bite, strike, or rattle, but rather to use their camouflage to stay hidden and quiet. If they believe they have been spotted, their second strategy is to escape, and they will begin to back away while rattling. However, if they are cornered or believe they cannot escape, they will rattle aggressively and form a coil with their head raised and neck in an ‘S’ shape. If you see a rattlesnake assuming this position, they are likely to strike if approached further. Back away slowly and give the snake plenty of space and they will relax. Biting is the last resort of a rattlesnake, and most bites on humans are the result of handling or accidentally stepping on one.

Western Rattlesnakes rely heavily on their hollow fangs to inject their prey with venom and get the nourishment they need through the summer. The fangs are folded back in the roof of the mouth when not in use, and flip forward when ready to strike. Because the fangs are so important, they have several replacements at the ready so that if a set breaks, another pair is waiting to take their place.

Species Account Author: Marcus Atkins

References

B.C. Conservation Data Centre. 2013. Species Summary: Crotalus oreganus. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed Jun 18, 2021). 
B.C. Conservation Data Centre. 2018. Conservation Status Report: Crotalus oreganus. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed Jun 18, 2021). 
B.C. Conservation Data Centre. 2021. BC Species and Ecosystems Explorer. B.C. Minist. of Environ. Victoria, B.C. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed Jun 18, 2021). 
COSEWIC. 2015b. COSEWIC assessment and status report on the Western Rattlesnake Crotalus oreganus in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. xi + 44 pp 
Environment and Climate Change Canada. 2019e. Recovery Strategy for the Western Rattlesnake (Crotalus oreganus), the Great Basin Gophersnake (Pituophis catenifer deserticola) and the Desert Nightsnake (Hypsiglena chlorophaea) in Canada. Species at Risk Act Recovery Strategy Series. Environment and Climate Change Canada, Ottawa. Part 1, 28 pp., Part 2, A. 37 pp., B. 36 pp., C. 28 pp. 
Southern Interior Reptile and Amphibian Working Group. 2016e. Recovery plan for the Western Rattlesnake (Crotalus oreganus) in British Columbia. Prepared for the B.C. Ministry of Environment, Victoria, BC. 37 pp. 
http://www.canadianherpetology.ca/species/species_page.html?cname=Western%20Rattlesnake 
http://linnet.geog.ubc.ca/efauna/Atlas/Atlas.aspx?sciname=Crotalus%20oreganus 
https://www.bcreptiles.ca/snakes/n_pacificrattle.htm 2