Sidewinder

## Description

The sidewinder (Crotalus cerastes ), also known as the horned rattlesnake and sidewinder rattlesnake, is a venomous pit viper species belonging to the genus Crotalus (the rattlesnakes), and is found in the desert regions of the Southwestern United States and northwestern Mexico. Three subspecies are currently recognized.

## Appearance

The sidewinder is a venomous snake found in the desert regions of North America. The color pattern of these snakes consists of a ground color that may be cream, buff, yellowish-brown, pink, or ash gray, overlaid with 28-47 dorsal blotches subrhombic or subelliptical in shape. Their belly is white and the proximal lobe of the rattle is brown in adults. The coloration of sidewinders can change depending on the temperature-a process known as metachrosis. Females in this species are larger than males, which is unusual for this group of snakes.

## Distribution

Sidewinders are found in the southwestern United States and northwestern Mexico. In the southwestern United States, these snakes are found in southeastern California, southern Nevada, southwestern Utah, and western Arizona. In northwestern Mexico, they are found in western Sonora and eastern Baja California. Sidewinders live in desert landscapes including sandy washes, sand dunes with thickly vegetated areas, and rocky areas.

## Behavior

Sidewinders are terrestrial snakes and rarely climb into vegetation. They are nocturnal during hot months and become diurnal during the cooler months, which is roughly from November to March. In order to stay cool, sidewinders spend most of their time in rodent burrows, the rest time is spend lying coiled up partially buried in the sand waiting on prey. These snakes take their common name from an unusual form of locomotion. As their body progresses over loose sand, they form a letter J-shaped impression, with the tip of the hook pointing in the direction of travel. Sidewinder rattlesnakes can use sidewinding to ascend sandy slopes, allowing them to ascend up to the maximum possible sand slope without slip. These snakes are generally lead a solitary life but may gather in groups during hibernation or denning; hibernation takes place in the burrows of rodents or desert tortoises. Newborn sidewinders have unique homeothermy (thermoregulation) behavior that has not been observed in any other type of snake. Following birth, the neonates mass together in their natal burrow. For the first week or so of their lives, newborns literally plug the entrance to this burrow during daylight hours, forming a dynamic multiple-individual mass that takes advantage of the hot exterior environment and the cool interior of the burrow to maintain an average aggregate temperature of 32 °C (the optimal temperature for shedding). The dynamic mass and constant movements of neonates modifies the thermal environment at the burrow entrance such that the young can occupy a location that would ordinarily become lethally hot for an individual neonate (or even an adult).

## Venom

These snakes are venomous, but possess a weaker venom than many other rattlesnakes. This, together with the smaller size of their venom glands, makes them less dangerous than their larger relatives. Regardless, any rattlesnake bite can be fatal and should be taken seriously and medical attention sought immediately.

Norris (2004) lists these venom yields: 33 mg average and 63 mg maximum (Klauber, 1956), and 30 mg average and 80 mg maximum (Glenn & Straight, 1982). Brown (1973) gives a venom yield of 33 mg (Klauber, 1956) and LD50 values for mice of 2.6 mg/kg IV, 3.0, 4.0, 2.3 mg/kg IP and 5.5 mg/kg SC for toxicity. With these figures, Brown calculated that the LD50 for an adult human being weighing 70 kg would be 385 mg (SC).

Envenomation can cause pain, swelling, hemorrhagic bleb formation, and ecchymosis (i.e., bruising). Swelling, while not particularly severe, occasionally may involve entire limbs and the trunk. Envenomation's systemic symptoms include nausea, dizziness, chills, coagulopathy (blood disorders), and shock. Klauber (1997) includes an account of a man who had been bitten on the first joint of the index finger of the right hand, with only a single fang penetrating. Although the bite was described as no more painful than a pin prick, a doctor was seen within about 25 minutes, and 10 cm3 of antivenin were administered. Within 2.5 hours, his entire arm was swollen and the pain was severe, "as if the arm were soaked in a bucket of boiling oil."

Ovine-derived antivenom, CroFab, for North American pit viper envenomation, has been widely available since 2001. Consultation with a local expert or regional poison control center should be obtained before administering antivenom. The previous antivenin (ACP) is no longer manufactured.

## Diet

Sidewinders are carnivores. They feed on rodents such as mice and rats, but also lizards, snakes, and birds. Juveniles prefer to hunt lizards.

## Reproduction

Sidewinders are polygynous, where males mate with multiple females. They mate in April through May and sometimes in fall. Females give birth to 5-18 live young in late summer to early fall after the gestation period that lasts around 4-5 months. The young are born 15-20 cm (6-8 inches) long. Within a few minutes of being born, the baby sidewinder escapes from a thin, transparent membrane. The young stay at their natal burrow for 7-10 days until they shed; during this time, the mother guards and protects them from predators. After that, the young disperse and have no future contact with their mother or their litter mates. Sidewinders usually mature at two to three years of age.

## Population

### Population threats

There are no major threats to sidewinders at present.

### Population number

According to IUCN, the sidewinder 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.