Crotalus scutulatus

Common names: Mohave rattlesnake,^[2][3][4] Mojave green,^[3] more.

Crotalus scutulatus is a venomous pitviper species found in the deserts of the southwestern United States and central Mexico. It is perhaps best known for its potent venom. Two subspecies are recognized, including the nominate subspecies described here.^[5]

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Description

  This species grows to an average of less than 100 cm in length, with a maximum of 137.3 cm.^[4]

The color varies from shades of brown to pale green depending on the surroundings. The green hue found among Mohave rattlesnakes has led to them being known as "Mohave greens" in some areas. Like C. atrox (the Western Diamondback rattlesnake), which it closely resembles, the C. scutulatus has a dark, diamond pattern down its back. However, with C. scutulatus the white bands on the tail tend to be wider than the black, whereas the band width is usually more equal in C. atrox. Additionally, C. scutulatus has enlarged scales on top of the head between the supraoculars and the light post-ocular stripe passes behind the corner of the mouth. In C. atrox, the crown is covered in small scales and the light post-ocular stripe intersects the mouth.^[6][3]

Common names

Mohave rattlesnake,^[2][3][7] Mojave green,^[3] Mojave diamond rattlesnake, Mojave rattlesnake, desert diamond back, Mojave rattler, scutulated rattlesnake.^[7] In Mexico, this species is known as Chiauhcóatl (Nahuatl), or víbora de cascabel (rattle-snake in Spanish).^[4] C. s. scutulatus has also been referred to as the northern Mohave rattlesnake.^[5]

Campbell and Lamar (2004) support the English name "Mohave rattlesnake" because it is widespread and well known, but do so with some reluctance because so little of the snake's range lies within the Mohave Desert. They also support the spelling "Mohave", as opposed to "Mojave", because the name is derived from the Native American term hamakhava.^[4]

Geographic range

  Found in the southwestern United States in southern California, southern Nevada, extreme southwestern Utah, most of Arizona, southern New Mexico and western Texas. Also ranges southward through much of Mexico to southern Puebla. It is found in deserts and other areas with xeric vegetation from near sea level to about 2500 m altitude. No type locality is given. Smith and Taylor (1950) proposed "Wickenburg, Maricopa county, Arizona" (USA), while Schmidt (1953) listed the type locality as "Mojave Desert, California" (USA).^[1] See map at right.

Habitat

Primarily a snake of high desert or lower mountain slopes, they are often found near scrub brush such as mesquite and creosote, but may also reside in lowland areas of sparse vegetation, among cacti, Joshua tree forests, or grassy plains. They tend to avoid densely vegetated and rocky areas, preferring open arid habitats.^[8]

Conservation status

This species is classified as Least Concern (LC) on the IUCN Red List of Threatened Species (v3.1, 2001).^[9] 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.^[10]

Behavior

Most active from April to September, and hibernate alone or in small groups during the winter. Ambush predators, they eat mostly small rodents and lizards. Females bear live young, from two to seventeen (average about eight), from July through September.^[3][11] Although they have a reputation for being aggressive towards people, such behavior is not described in the scientific literature. Like other rattlesnakes, however, they will defend themselves vigorously when disturbed.

Venom

Rattlesnake venoms are complex cocktails of enzymes and other proteins that vary greatly in composition and effects, not only between species, but also between geographic populations within the same species. C. scutulatus is widely regarded as producing one of the most toxic snake venoms in the New World, based on LD₅₀ studies in laboratory mice.^[12] Their potent venom is the result of a presynaptic neurotoxin composed of two distinct peptide subunits.^[13] The basic subunit (a phospholipase A₂) is mildly toxic and apparently rather common in North American rattlesnake venoms.^[14] 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.^[14] However, not all populations express both subunits. The venom of many Mohave rattlesnakes from south-central Arizona lacks the acidic subunit and has been designated “Venom B,” while Mohave rattlesnakes tested from all other areas express both subunits and have been designated “Venom A” populations.^[15] Based on median LD₅₀ values in lab mice, Venom A bite from Mohave rattlesnakes is more than ten times as toxic as Venom B, which lacks Mojave toxin.^[16]

Bite symptoms

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.^[17]

In people bitten by Venom A Mohave rattlesnakes (those outside the relatively small Venom B area in south-central Arizona), the onset of serious signs and symptoms can be delayed, sometimes leading to an initial underestimation of the severity of the bite. Significant envenomations (as with all snakebites, the amount of venom injected is highly variable and unpredictable) can produce vision abnormalities and difficulty swallowing and speaking; in severe cases, skeletal muscle weakness can lead to difficulty breathing and even respiratory failure.^[17] Contrary to popular belief, fatalities are uncommon.^[18][19]

Antivenin

Unlike the rattlesnake antivenin used in the United States over the previous fifty years, CroFab^TM antivenin (approved by the USFDA in October 2000) uses Mohave rattlesnake Venom A (in addition to venom from three other species) in its manufacture,^[20] making it particularly effective for treatment of Venom A Mohave rattlesnake bites. Antibodies in CroFab^TM produced by the other three species' venoms effectively neutralize Mohave rattlesnake Venom B.

Subspecies

See also

• List of crotaline species and subspecies
• Crotalus by common name
• Crotalus by taxonomic synonyms
• Crotalinae by common name
• Crotalinae by taxonomic synonyms
• Snakebite

References