Mojave Rattlesnake

## Description

Crotalus scutulatus (common names: Mojave rattlesnake, Mojave green,) is a highly venomous pit viper species found in the deserts of the southwestern United States and central Mexico. It is perhaps best known for its potent neurotoxic-hemotoxic venom, which is considered one of the world's most potent rattlesnake venoms. Two subspecies are recognized, including the nominate subspecies described here.

## Appearance

Mojave rattlesnake is a highly venomous and dangerous pit viper species found in the southwestern United States and central Mexico. It is perhaps best known for its potent venom, which is considered one of the world's most potent rattlesnake venom. These snakes have a heavy body and a large triangular head. Their color varies from shades of brown to pale green depending on the surroundings. The green hue found among Mojave rattlesnakes has led to them being known as "Mojave greens" in some areas. They also have a dark diamond pattern along their back and the light postocular stripe that passes behind the corner of the mouth.

## Distribution

Mojave rattlesnakes are found in the southwestern United States in southern California, southern Nevada, northern and eastern Nevada, extreme southwestern Utah, most of Arizona, southern New Mexico, and some of Texas. They are commonly found in Riverside, California. They also range southward through much of Mexico to southern Puebla. These snakes live in deserts and other areas with xeric vegetation. They are often found near scrub brush such as sage mesquite and creosote, but may also reside in lowland areas of sparse vegetation, among cacti, Joshua tree forests, or grassy plains. They can also range up the Eastern Sierra as far north as Reno and perhaps beyond into southern Eastern Oregon. Mojave rattlesnakes tend to avoid densely vegetated and rocky areas, preferring open, arid habitats.

## Behavior

Mojave rattlesnakes are mainly nocturnal and during the heat of day hide in burrows of other mammals or under rocks. However, during cooler days they may come out during the day to bask in the sun. These snakes are most active from April to September and brumate alone or in small groups during the winter. They have a reputation for being aggressive towards people and like other rattlesnakes, they will defend themselves vigorously when disturbed. When frightened, Mojave rattlesnakes shake their tail, producing a buzzing sound; this way they warn an intruder before striking. They have also been known to come towards and chase humans.

## Venom

Their potent venom is the result of a presynaptic neurotoxin composed of two distinct peptide subunits. The basic subunit (a phospholipase A2) is mildly toxic and apparently rather common in North American rattlesnake venoms. The less common acidic subunit is not toxic by itself, but in combination with the basic subunit, produces the potent neurotoxin called "Mojave toxin". Nearly identical neurotoxins have been discovered in five North American rattlesnake species besides C. scutulatus. However, not all populations express both subunits. The venom of many Mojave rattlesnakes from south-central Arizona lacks the acidic subunit and has been designated "venom B", while Mojave rattlesnakes tested from all other areas express both subunits and have been designated "venom A" populations.

Called "Mojave toxin". Nearly identical neurotoxins have been discovered in five North American rattlesnake species besides C. scutulatus. However, not all populations express both subunits. The venom of many Mojave rattlesnakes from south-central Arizona lacks the acidic subunit and has been designated "venom B", while Mojave rattlesnakes tested from all other areas express both subunits and have been designated "venom A" populations.

Venom differences

Based on median LD50 values in lab mice, venom A from subspecies A Mojave rattlesnakes is more than ten times as toxic as venom B, from type B Mojave green rattlesnakes, which lacks Mojave toxin. Medical treatment as soon as possible after a bite is critical to a positive outcome, dramatically increasing chances for survival.

However, venom B causes pronounced proteolytic and hemorrhagic effects, similar to the bites of other rattlesnake species; these effects are significantly reduced or absent from bites by venom A snakes. Risk to life and limb is still significant, as with all rattlesnakes, if not treated as soon as possible after a bite.

## Diet

Mojave rattlesnakes are carnivores and eat mostly lizards, toads, birds and small rodents, such as mice, rats, and rabbits.

## Reproduction

The breeding season for Mojave rattlesnakes starts in July and lasts until September. Females give birth to 2-17 live young, usually in abandoned rodent burrows. The young are born fully-developed and measure around 25 cm from head to tail.

## Population

### Population threats

There are no major threats facing Mojave rattlesnakes at present.

### Population number

According to IUCN, the Mojave rattlesnake is locally common and widespread throughout its range but no overall population estimate is available. Currently, this species is classified as Least Concern (LC) on the IUCN Red List and its numbers today are stable.

### Ecological niche

Mojave rattlesnakes are important predators of lizards and many small rodents, such as rats and mice, which make a big portion of their diet.