Northern Pacific Rattlesnake

Western Rattlesnake
Crotalus oreganus oreganus

We meet the majority of Edgewood’s creatures with, as Emily Dickinson wrote, “a transport of cordiality,” but for this one we may feel “a tighter breathing and zero at the bone.”

Our Northern Pacific rattlesnake is a member of the Northern American pit viper group, sharing the group’s characteristic heavy body, triangular head, keeled scales, elliptical pupils, large hollow fangs attached to poison glands, and loreal pits for detecting heat from warm bodies. Fortunately, the Northern Pacific rattlesnake is more pacific than most pit vipers!

Appearance

Northern Pacific rattlesnakes are thick-bodied, medium-to-large snakes with a triangular head and a rattle-tipped tail. They are typically 2-3 feet long, but may be longer. Their background skin color is light and variable, generally matching the soil of their environment, and can be shades of tan, olive, brown, gray, yellowish, or gold. Dark blotches on their back are usually outlined in a lighter color. These markings help them blend into their environment. Their rattle consists of shed tail scales that click against each other when the snake shakes its tail, making a rattling sound.

Their eye pupils are vertical, which suggests good night vision, and they usually have a light stripe running from behind their eyes to the corner of their mouth – but don’t look too closely to see these details!

Newborn pups are about 10 inches long, light in color, and born with a bright yellow tail button that doesn’t rattle.

That Rattle

A rattlesnake’s rattle is made up of loosely interlocking segments of keratin, which is the same protein that’s in our fingernails. Each segment is held in place by the one in front and behind it, but the individual segments can move a bit. Rattlesnakes add a new segment to their rattle each time they shed their skin. Rattlesnake pups are born with a bright yellow button at the end of their tail. After about 2 weeks they will shed their skin for the first time and add a new segment. After two rounds of shedding, the pups will have a new rattle segment that can make a noise.

Fangs

Rattlesnakes keep their long fangs tucked in their mouth with a special hinge mechanism: the hinged fangs can rotate from a passive position, folded back against the upper jaw, to a perpendicular biting position. The fangs are hollow and have a duct at the base which connects to individual venom glands. The snake can control the release of venom from each fang using pressure on a sphincter located by the venom gland. Fangs are shed and replaced about every 2 months by a new set of replacement fangs lining the upper jaw.

Venom

A rattlesnake is “venomous” and not “poisonous.” A simple way to think about the difference is that a venomous thing bites you and a poisonous thing is bitten by you. Rattlesnake venom, which the snake uses to immobilize prey, is composed of a combination of toxins and enzymes. These include hemotoxins, which can cause bleeding and tissue damage; neurotoxins, which can cause paralysis; and enzymatic proteins, which can break down tissues.

ID Tips

At first startled glance, the Pacific gopher snake may be mistaken for a rattlesnake since both are large snakes with mottled coloring. The triangular head and rattle on the tail should be enough to distinguish the rattlesnake (though a young rattlesnake might only have a tail button). A gopher snake has a slender head and its long tail tapers to a point. Gopher snakes aren’t venomous and present no threat to humans.

At Edgewood

Protected open spaces like Edgewood provide the space and resources Northern Pacific rattlesnakes need to live and raise their young. They may be found in many Edgewood habitats, including scrub, grasslands, rocky outcrops, chaparral, and open woodlands. They may also be seen next to or on Edgewood trails.

See iNaturalist for observations of the Northern Pacific rattlesnake at Edgewood. Sightings have been recorded in Edgewood in every month except December and January.

The rattlesnakes at Edgewood (Crotalus oreganus oreganus) are a subspecies of the Western rattlesnake (Crotalus oreganus).

Habitat and Range

The Northern Pacific rattlesnake range is from southern Canada south to San Luis Obispo and Santa Barbara counties, and east to the Cascade Range, the western slope of the Sierra Nevada, and the Great Valley.

This subspecies occurs in moister habitats than other rattlesnakes found in California. It inhabits rocky hillsides, talus slopes and outcrops, rocky stream courses, rocky areas in grasslands, mixed woodlands, and sagebrush. Rattlesnakes love rock crevices, which are warm and full of rodents, and provide shade and protection from predators.

Diet

Northern Pacific rattlesnakes prey primarily on rodents such as mice, rats, gophers, voles, and squirrels. However, their diet may also include rabbits, hares, birds and their eggs, lizards, snakes, frogs, and insects. Newborn snakes eat insects, small rodents, and small lizards.

Several animals at Edgewood are immune to rattlesnake venom. These include woodrats, opossums, and kingsnakes. Rattlesnakes possess partial immunity to their own venom.

Predators

Rattlesnakes are prey for kingsnakes, hawks (especially red-tailed hawks), eagles, owls, coyotes, bobcats, and mountain lions.

Along with lying motionless in grass or rock cover, their camouflage coloration helps them avoid discovery by other predators. Because it’s an ambush predator, a rattlesnake won’t rattle its tail to signal its presence at every disturbance, and it can use its infrared detection to determine the size of an approaching animal. Although rattlesnakes are well-known for rattling their tail when feeling threatened, a rattlesnake may not rattle at all if it senses a potential predator.

Lifecycle

Northern Pacific rattlesnakes mate in the spring, with males searching for females after the snakes come out of their winter rest. Females start bearing young at about 3 years old and typically breed every 1-3 years, giving birth to live young in late summer or early autumn.

They often den in deep crevices of rock outcrops and in animal burrows. Sometimes several rattlesnakes gather at a rock outcrop to give birth and care for their pups in a communal nest called a rookery. A typical brood size is 4-12 pups. Mother rattlesnakes shield the babies and keep them from wandering from the shelter. Huddling together helps the newborns conserve heat and reduce water loss. Baby rattlesnakes receive care from mother rattlesnakes until about the time the pups first shed their skin, adding a new tail segment, about 2 weeks from birth. Normal lifespan is about 10-15 years.

Seasonal Behavior

Like all reptiles, rattlesnakes are cold-blooded, meaning they rely on external sources of heat, like the sun, to control their body temperature, so their activity varies with season and temperature. Northern Pacific rattlesnakes are most active from April to October and are most likely to be out when we would be comfortable in a T-shirt and shorts. In the spring and fall they are active during the daytime (diurnal) or at dawn and dusk (crepuscular).

When the sun is blazing on hot summer days, they seek shade to avoid overheating; at night, when the temperature lowers, they are most active, coming out after sunset.

In late fall and winter when the ground temperature cools, the snakes typically seek sheltered locations such as rodent burrows or rock crevices to enter a dormancy period which may last several months. This dormancy is known as brumation and is similar to hibernation in mammals, except the snakes don’t actually sleep, but simply become lethargic. Their metabolism slows, and they are inactive with occasional periods of activity, sometimes emerging to bask in the midday sun to raise their body temperature.

Often multiple rattlesnakes may gather and establish dens, called hibernacula, during the colder months. A hibernaculum, often found in rocky crevices where heat is retained, provides refuge and opportunities for family interaction, and is usually composed of extended family groups.

Special Sensory Organs

Northern Pacific rattlesnakes usually hunt at night, using an ambush strategy to capture rodents and other small mammals. Along with good night vision, rattlesnakes have two special sensory organs that help them detect prey. These organs are the vomeronasal organ (also called Jacobsen’s organ), which all snakes have, and the loreal pits, which only pit vipers have.

Vomeronasal organs detect chemicals, which helps the snakes identify friend, foe, or food in their surroundings. Located in the nasal septum above the roof of the snake’s mouth, these sensory organs have small openings into the mouth. A flick of the snake’s forked tongue picks up chemicals from the environment and delivers the chemicals to the openings for information processing. Sometimes described as “smelling” with the tongue, this system is finely tuned for scent tracking, providing information for hunting even in darkness. Each tine of the forked tongue can pick up different concentrations of scent particles, which helps determine the direction of the smells. Snakes can smell in stereo!

Loreal pits are a type of infrared detector, located near the nostrils on each side of the head. The pits are directed forward, similar to binoculars, and so allow depth perception from heat radiated from warm objects, aiding in hunting and navigation. Pit vipers such as the rattlesnake can sense a temperature change of less than half a degree, accurately locating warm-blooded prey even in complete darkness.

Thus equipped, a rattlesnake uses chemical detection to find frequently used small-mammal pathways where it can select an ambush site nearby, and can use infrared detection to accurately strike a warm prey animal even at night.

After biting the rodent or mammal, the snake releases the envenomed animal, which doesn’t die immediately, but scurries away until the venom takes effect. Having learned the victim’s scent at the moment of the bite, the snake then follows the chemical scent trail of their bitten prey to swallow it whole.

Name Derivation

• Crotalus – from the Greek krotalon, “rattle,” referring to the tail rattle
• oreganus – Latin for “belonging to the state of Oregon,” referring to the species’ type locality, which was first identified on the banks of the Columbia River

Fun Facts

• Counting the segments of the tail won’t tell you the snake’s age. A rattle segment is added to the end of the tail every time a rattlesnake sheds its skin. A young rattler may add 3 or 4 segments each year, but a mature snake may shed only once a year. How often a rattlesnake sheds its skin depends more on how well fed it is, rather than how old it is. Also, segments can break off — sometimes from predator attacks, sometimes from normal wear and tear — so the rattle can look blunted.
• Rattlesnakes use special high-performance muscles to shake their tail, causing the loose segments to click against each other as undulating waves move down the rattle. With the tail shaking at 50-100 times per second, all we sense is a buzz and a blur. It’s said to be one of the fastest sustained muscular contractions in the natural world — right up there with a hummingbird’s wings — and they can shake for up to 2 hours.
• Rattlesnake folklore has it that bites from baby rattlesnakes are worse than bites from adults; however rattlesnake experts dismiss this as a myth. The reasoning behind the myth is that the babies have not yet learned to control their venom, so they inject all the venom they have, whereas experienced adults will titrate the amount of venom they inject or even give a dry bite. However, bigger snakes have bigger venom sacs, and can deliver much more venom even if they inject only a small percentage of the total amount available. The potential severity of a bite from an adult is significantly higher than that from a baby rattlesnake.

Learn More

California Poison Control System. 2026. Rattlesnakes.

Morey, S. 2014. Western rattlesnake. California Wildlife Habitat Relationship System. State of California, Department of Fish and Wildlife.

Nelson, G. 2024. Western rattlesnake (Northern Pacific rattlesnake). AZ Animals. Flywheel Publishing, Lakewood, Colorado.

Project Rattlecam.

State of California, Department of Fish and Wildlife. Rattlesnake.

References

Ellis, M. 2015, Oct. 1. Ask the naturalist: Do rattlesnakes migrate? Bay Nature.

Ferreira, G. 2024, Apr. 19. Ask an expert: How do I stay sssafe during rattlesnake season? Cal Poly News.

Hawkes, A 2013. It’s rattlesnake season – beware! Bay Nature.

Iwane, T. 2018, May 1. Ask the naturalist: Are baby rattlesnakes the most dangerous biters? Bay Nature.

Iwane, T. 2019, July 2. Ask the naturalist: How can you tell a gopher snake from a rattlesnake? Bay Nature.

Linn, S. 2026, Feb. 3. Where do rattlesnakes go in California when it’s cold? What experts say. Sacramento Bee.

Lueneburger, K. The Western Rattlesnake (Crotalus viridis). Western Rattlesnake Natural History. University of Oregon.

Stebbins, R. 2012. Field Guide to Amphibians and Reptiles of California (revised ed.). University of California Press, Berkeley and Los Angeles, California.

Taylor, E. 2024. California Snakes and How to Find Them. Heyday, Berkeley, California.