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Latreille In Sonnini & Latreille, 1801
- Common names: Middle American rattlesnake, Central American rattlesnake,, Tzabcan (local name for subspecies C. s. tzabcan).
Crotalus simus is a venomous pitviper species found in Mexico and Central America. The specific epithet is Latin for "flat nosed"; likely an allusion to the fact that its head is relatively blunt when compared with the lanceheads (Bothrops). Currently, 3 subspecies are recognized, including the nominate subspecies described here.
Adults commonly exceed 130 cm in length, with males growing larger than females. Large males reach 140-160cm in some populations. The maximum reported length is 180 cm.
The body has an exceedingly rough appearance as the normal dorsal scale keels are accentuated into protuberances or tuberculations. This is most apparent on the scale rows to either side of the vertebral scales, with a decreasing intensity in the lower rows. The vertebral scales are about as prominently keeled as the fourth row down on the flanks (with the vertebral scales as the first row).
Found from Mexico in southwestern Michoacán on the Pacific coast, and Veracruz and the Yucatan Peninsula on the Atlantic coast, south through Belize, Guatemala, El Salvador, Honduras and Nicaragua to west-central Costa Rica. It is absent from Panama, but apparently does occur on the Atlantic side of Colombia. The type locality given is "Ceylan," which is incorrect.
Usually found in regions that are semiarid, including tropical forests that are dry or very dry, thorn woodland and arid scrub forest. It also occurs in mesic forests with relatively dry open areas.
To the Mayans and their living descendants, the Yucatan subspecies (C. s. tzabcan) was greatly revered. The word tzabcan means rattlesnake in Mayan. It is unknown what the rattlesnake actually symbolizes, but many temples have had rattlesnake shapes carved. Shamans also dry and roast snakes, grinding them into a powder used as medicine. 
Bites from this species are similar to rattlesnake bites in the United States. Local symptoms may be severe, with pain, massive swelling, blistering and necrosis that often lead to physicians performing fasciotomies and in some cases amputations. Systemic effects involving hemostatic disturbances are rare, as are renal failure and neurotoxicity. Only venom from neonates contains crotoxin; a constituent typically found in C. durissus venom that produces neurotoxic symptoms.
|Subspecies||Taxon author||Common name||Geographic range|
|C. s. culminatus||Klauber, 1952||Northwestern neotropical rattlesnake||Mexico in southwestern Michoacán, southern and western Morelos, Guerrero and southwestern Oaxaca. It probably also occurs in extreme western Puebla and possibly in the Mexican Federal District.|
|C. s. simus||Latreille In Sonnini & Latreille, 1801||Central American rattlesnake||Southeastern Mexico (central Veracruz, southeastern Oaxaca, Tabasco and Chiapas), central and southern Guatemala, western and southern Honduras, southern Belize, El Salvador, southwestern Nicaragua, and northwestern and central Costa Rica.|
|C. s. tzabcan||Klauber, 1952||Yucatán neotropical rattlesnake||Mexico (Yucatán, Campeche, Quintana Roo and eastern Tabasco), northern Guatemala and northern Belize.|
Previously, the description for this form was listed as the nominate subspecies for the tropical rattlesnake, C. durissus. Molecular genetic data suggest that the taxa culminatus and tzabcan should be considered as separate species from C. simus 
- List of crotaline species and subspecies
- Crotalus by common name
- Crotalus by taxonomic synonyms
- Crotalinae by common name
- Crotalinae by taxonomic synonyms
- ^ a b c d e Campbell JA, Lamar WW. 2004. The Venomous Reptiles of the Western Hemisphere. 2 volumes. Comstock Publishing Associates, Ithaca and London. 870 pp. 1500 plates. ISBN 0-8014-4141-2.
- ^ a b c 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).
- ^ a b c d Klauber LM. 1997. Rattlesnakes: Their Habitats, Life Histories, and Influence on Mankind. Second Edition. 2 volumes. Reprint, University of California Press, Berkeley. ISBN 0-520-21056-5.
- ^ a b c Crotalus simus (TSN 727493). Integrated Taxonomic Information System. Retrieved on 28 August 2007.
- ^ Citation needed
- ^ Warrell DA. 2004. Snakebites in Central and South America: Epidemiology, Clinical Features, and Clinical Management. In Campbell JA, Lamar WW. 2004. The Venomous Reptiles of the Western Hemisphere. Comstock Publishing Associates, Ithaca and London. 870 pp. 1500 plates. ISBN 0-8014-4141-2.
- ^ Wüster, W., J.E. Ferguson, J.A. Quijada-Mascareñas, C.E. Pook, M.G. Salomão & R.S. Thorpe (2005) Tracing an invasion: landbridges, refugia and the phylogeography of the Neotropical rattlesnake (Serpentes: Viperidae: Crotalus durissus). Molecular Ecology 14(4): 1095-1108.