Crotalus cerastes, Photo: Michael Lahanas
Crotalus cerastes Hallowell, 1854
Crotalus cerastes is a venomous pitviper species found in the desert regions of the southwestern United States and northwestern Mexico. Three subspecies are currently recognized, including the nominate subspecies described here.
A small species, with adult specimens measuring between 43 cm and 76 cm (17 to 30 in) in length. According to Campbell and Lamar (2004), most adults are 50–80 cm (19.8 to 32 in) in length. The females are larger than the males, which is unusual for this group of snakes.
Midbody there are usually 21 rows of keeled dorsal scales. In males there are 141 or fewer ventral scales; in females 144 or fewer. Sometimes referred to as the horned rattlesnake because of the raised supraocular scales above its eyes. This adaptation may help shade the eyes or prevent sand drifting over them as the snake lies almost buried in it.
The color pattern consists of a ground color that may be cream, buff, yellowish brown, pink or ash gray, overlaid with 28-47 dorsal blotches that are subrhombic or subelliptical. In the nominate subspecies, the belly is white and the proximal lobe of the rattle is brown in adults. Klauber and Neill describe the ability of this species to display different coloration depending on the temperature—a process known as metachrosis.
Sidewinder, horned rattlesnake, sidewinder rattlesnake, Mojave Desert sidewinder (for C. c. cerastes), sidewinder rattler.
In the southwestern United States this species is found in the desert region of eastern California, southern Nevada, extreme southwestern Utah and western Arizona. In northwestern Mexico it is found in western Sonora and eastern Baja California. The type locality is listed as the "borders of the Mohave river, and in the desert of the Mohave" (California).
This species is classified as Least Concern (LC) on the IUCN Red List of Threatened Species (v3.1, 2001). Species are listed as such due to their wide distribution, presumed large population, or because it is unlikely to be declining fast enough to qualify for listing in a more threatened category. The population trend is stable. Year assessed: 2007.
The species is nocturnal during hot months and diurnal during the cooler months of its activity period, which is roughly from March to November (probably longer in the southern part of its range).
Juvenile Sidewinders use their tails to attract lizard prey (see video: ), a behavior termed "caudal luring". Adult Sidewinders lose this behavior as they make the transition from lizard prey to their primary diet of desert rodents. Sidewinder juveniles appear to mimic both life stages of lepidopterans in their luring motions. Their fast luring motions resemble the fluttering of a moth and their slower tail movements resemble a caterpillar. Both movements have been observed to attract prey lizards.
Neonatal sidewinders engage in a remarkable type of behavioral homeothermy that has not been observed in any other type of snake. Following birth, the neonates mass together in their natal burrow. Most often, gravid females select an East facing, small diameter rodent burrow to birth in. For the first week or so of their lives, neonatal sidewinders literally plug the entrance to this burrow during daylight hours, forming a dynamic multi-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). Experiments showed that the dynamic mass 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). Because of the constant movements of the neonates, the aggregate assumes stable temperature properties reminiscent of a homeothermic organism (i.e., maintains tight temperature tolerance ± 2°C).
Females produce up to 18 young, with an average of about 10 per litter. Like most other viperids, the young are born enveloped in thin embryonic membranes out of which they emerge shortly after being expelled from the mother. The young stay with their mother in a burrow for 7–10 days, shed for the first time, then leave their natal burrow. During this time, it is thought that the mother guards and protects them from predators.
Sidewinders mature at 2–3 years of age, are capable of reproducing annually, and give birth to live young. Some females skip reproductive opportunities. Some might even skip two years, if the food supply is scarce. Sidewinders mate in April through May and sometimes in fall. When the male and female mate, the male snake crawls along the female's back, rubbing her with his chin to stimulate or arouse her. The male then will wrap his tail around her tail and then will try to bring their clocque together. The clocque is a little flap that is near tail which is designed for mating and reproduction. If the female wants to mate, she will lift her tail and allow him to mate with her. The snakes can be mating for several hours, and if one of the snakes decides to move, the other is dragged along. Females might mate with several males in a season. Females give birth to 5-18 young in late summer to early fall. The young are born 6 to 8 inches long. The birth takes only 2 to 3 hours altogether. Within a few minutes after being born, the baby sidewinder escapes out of a thin transparent membrane. The young stay at their natal burrow for 7–10 days until they shed and then they disappear and have no future contact with their mother or their littermates. While the density of sidewinders can be up to 1 individual per hectare, individuals rarely encounter each other except during mating season.
Sidewinders have an extraordinarily accelerated life cycle, with natural life expectancies of females of about five years. Males may live quite a bit longer (max known natural life span of 13 years). Sidewinders can live more than 20 years when well fed in captivity (even females). Thus, it appears that energetics factor heavily into natural female mortality, whereas predation might be the primary pressure on males. In the wild, females often die of post-birth exhaustion, but the lives of sidewinders are also cut short because of predation, diseases, and vehicle encounters.
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 cousins. Still, any rattlesnake bite can be fatal and should be taken seriously and medical attention sought immediately.
Norris (2004) lists the following 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).
Bites can cause pain, swelling, hemorrhagic bleb formation and ecchymosis. Any swelling is usually not particularly severe, but it can involve all of the affected limb as well as the trunk. Systemic symptoms can include nausea, dizziness, chills, coagulopathy 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 itself was described as no more painful than a pin prick, a doctor was seen within about 25 minutes and 10 cc of antivenin had been administered, within 2.5 hours his entire arm had swelled and the pain was violent, "as if the arm were soaked in a bucket of boiling oil."
1. ^ a b McDiarmid RW, Campbell JA, Touré T. 1999. Snake Species of the World: A Taxonomic and Geographic Reference, vol. 1. Herpetologists' League. 511 pp. ISBN 1-893777-00-6 (series). ISBN 1-893777-01-4 (volume).
Source: Wikipedia, Wikispecies: All text is available under the terms of the GNU Free Documentation License