Crotalus basiliscus

Common names: Mexican west coast rattlesnake,^[2] Mexican green rattler,^[3] more.

Crotalus basiliscus is a venomous pitviper species found in western Mexico. The specific name is derived from the Greek word for king, basiliskos, and is an allusion to this snake's large size and potent venom.^[2] No subspecies are currently recognized.^[4]

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Description

  This is one of the largest rattlesnake species. Specimens exceeding 150 cm are not uncommon, while the maximum size reported is 204.5 cm (Klauber, 1972).^[2] The body is moderately stout and rather rectangular in cross section.^[5]

Midbody there are 25-29 rows of strongly keeled dorsal scales. The ventral scales number 174-206 and the subcaudals 18-36.^[5]

The color pattern consists of brown or grayish ground color overlaid with 26-41 dark, rhomb-shaped (diamond) blotches with light edges.The head is a uniform grayish brown except for its lighter labial scales and dark postorbital bar. There is no distinct pattern on the crown or neck areas. The tail may be gray, with darker bands, or almost uniform in color without any distinct markings. The belly is white or cream colored.^[5] The young are mostly red, but adults eventually become an olive green.^[3] Within its range, this is the only rattlesnake that has diamond-shaped dorsal markings.^[5]

This species often occurs in the same areas as C. molossus and in these places the two appear to hybridize freely. While these two species are easily distinguished, identifying the hybrid specimens is problematic.^[2]

Common names

Mexican west coast rattlesnake,^[2] Mexican green rattler,^[3] Mexican west coast green rattlesnake.^[6]

Geographic range

Found in western Mexico from southern Sonora to Michoacán,^[1] where it is mostly restricted to the coastal plain.^[3] The type locality given is "Near Colima, Mexico."^[1]

Habitat

Around Colima, where this species is (or was at one point) particularly plentiful, the are has been described as mostly treeless and covered with short grass with scattered clumps of mesquite, acacias and other thorny bushes, as well as plenty of large cacti. It can be said that the habitat of C. basiliscus is mostly tropical thorn forest, with an extension up into tropical deciduous forest.^[3]

Conservation status

This species is classified as Least Concern (LC) on the IUCN Red List of Threatened Species (v3.1, 2001).^[7] 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 on trend is stable. Year assessed: 2007.^[8]

Behavior

In the lowlands, these snakes are primarily active during the rainy summer months and most are found crossing the roads at night. However, a few have been seen basking early in the morning.^[2] It has been reported that this species tames quickly in captivity.^[3]

Feeding

Klauber reported that seven specimens contained mammal hair, probably belonging to rodents.^[3]

Venom

This species is known to produce large amounts of highly toxic venom and large specimens should be regarded as very dangerous.^[5]

Brown (1973) mentions an average venom yield of 297 mg (dried venom), as well as LD₅₀ values of 11.1 mg/kg IV and 4.0 and 12.9 mg/kg IP.^[9]

In some populations, the venom may contain a component that is structurally related to Mojave toxin. The venom also contains proteases.^[10] Antivenin is produced by the Instituto Nacional de Higiene in Mexico.^[5] In the United States, Protherics in Brentwood, Tennessee, produces an antivenin called "Crotalidae Polyvalent Immune Fab (Ovine)" containing a paraspecific anti-body that protects against bites from this species.^[11]

Taxonomy

Before 1989, two subspecies were recognized: C. b. basiliscus and C. b. oaxacus. In that year, the latter subspecies was transfererred to C. molossus by Campbell and Lamar.^[1] Occasionally, one may also encounter references to another subspecies, C. b. totonacus (Gloyd & Kauffeld, 1940), found in northeastern Mexico. It was more commonly considered to be a subspecies of C. durissus,^[1] until recently when it was elevated to a full species by Campbell and Lamar (2004): Crotalus totonacus.^[2][12]

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