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Western Diamondback Rattlesnake
Western diamondback rattlesnake is unusually at home where people actually live. General reference material describes it as unusually adaptable to semi-urban habitat and notes that it is frequently encountered inside the Phoenix and Tucson metro areas, which is a different encounter pattern from the rural, backcountry one most rattlesnakes have. Nothing about it threatens a building. It chews nothing, nests in no wall, and damages no building material. The single risk it puts on the table is the bite, and on that count two separate lines of evidence agree. A peer-reviewed comparative venom study states that in the United States this species trails only eastern diamondback rattlesnake among the most medically dangerous native snakes, and general reference sources credit it with the greatest total number of snakebites of any species in the country. Independently, a peer-reviewed study of fatal snakebites in the United States between 1989 and 2018 found that rattlesnakes as a genus accounted for 90.2 percent of fatal bites where the species was known or could be inferred. Those are two different kinds of evidence, a laboratory venom comparison and a clinical mortality record, pointing in the same direction. What neither of them supports is the label people reach for first. It is not documented as the snake with the highest fatality count in the United States, and calling it that goes past the evidence.

Seasonal Timeline

Western diamondback rattlesnake is active from roughly early March through late October, hunting mostly at night and in the early morning and spending the cold months dormant in caves and burrows. Live young arrive late in the season, with births documented from late July through September.

Peak, South CentralMar–Oct
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Western diamondback rattlesnake is active from roughly early March through late October, hunting mostly at night and in the early morning…

This snake keeps two calendars at once, and the daily one runs opposite to what most people expect. Through the roughly March to October active season it hunts at night and in the early morning, and it is generally sedentary between hunts. Midday sun in open desert is a hazard to a snake, not an opportunity, so the daylight hours are spent in shade, under cover, or below ground. When temperatures fall for the year the animal moves into a cave or a burrow and stays dormant from about late October until early March. The practical consequence is that a property can hold this species for an entire season without anyone seeing it in daylight.

The reproductive calendar is the second one, and it is less regular than an annual cycle. Mating happens in spring and again in fall. A peer-reviewed field and laboratory study of 46 sexually mature Arizona females found enlarged ovarian follicles from February through June, ovulating that same year, and again from September through November, ovulating the following year. In other words yolk deposition spans two full activity seasons rather than one, so an individual female produces a litter in alternating years rather than every summer. Births then fall from late July through September, with the earliest neonates recorded in the field on August 8 through 11, which means small newly born snakes are moving through the same desert scrub, burrow mouths, and yard edges the adults have used all season.

Where They're Found

Western diamondback rattlesnake is an entirely outdoor, wild species. It is not a structural invader the way a rodent or a bat is, and nothing in its biology gives it a reason to get inside a building. Its range covers the South Central and Southwest states.

The range covers central and western Arkansas, Oklahoma apart from the northeast, north central, and panhandle areas, Texas apart from the northern panhandle and the easternmost and wettest portions, southern and central New Mexico, all of Arizona, extreme southern Nevada, and a corner of southeastern California near the Chocolate Mountains, continuing south through most of northern and central Mexico. Records from extreme southern Kansas suggest a possible isolated population there. Alaska and Hawaii have no western diamondback rattlesnake population, and one general reference states that absence outright rather than leaving it to inference. Every published range description confines the species to the arid and semi-arid South Central and Southwest United States and to Mexico.

Habitat breadth is the surprising part. For a desert rattlesnake this animal is a generalist, documented from flat coastal plain to steep rocky canyons and hillsides, and across desert scrub, sandy creosote flats, mesquite grassland, and even pine and oak forest at elevation, from below sea level up to about 6,500 feet. Rodent burrows and piles of rock and debris supply both shelter and winter denning sites. The detail that matters most for a homeowner is the one that separates this species from most other rattlesnakes: it is directly documented as highly adaptable to semi-urban habitat and as a frequent presence inside the Phoenix and Tucson metro areas. This is not strictly a backcountry animal, and a city address is not a reason to rule it out.

Diet explains most of the rest. Small mammals make up 94.8 percent of the diet by weight, including prairie dogs, kangaroo rats, pocket gophers, voles, woodrats, pocket mice, white-footed mice, fox squirrels, cotton rats, ground squirrels, rabbits, and jackrabbits, with large adults able to take an adult cottontail or jackrabbit. Birds such as mockingbirds, quail, owls, larks, and sparrows are secondary prey, along with lizards and the occasional insect or other reptile or amphibian. Under normal wild conditions it feeds roughly every two to three weeks, and it can go up to two years without food in extreme conditions. A western diamondback near a house is usually there because the rodents are.

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