This large rattlesnake can be found in Central American from Mexico to Costa Rica. It largely inhabits semi-arid dry tropical forests and coastal scrub forests, but can be found on the fringes of rainforests and meadow/grassland clearings nestled in the rainforest.

Crotalus simus was given its own species standing separate from Crotalus durissus in 2004. Since then, four subspecies & cryptic populations have been broken off and elevated to their own species status: C. tzabcan, C. culminatus, C. ehecatl and C. mictlantecuhtli. The Latin translation for "simus" is "flat-nosed."

A neonate Central American rattlesnake shares only 50% of the same venom proteome with an adult and includes more neurotoxic proteins. Much research has gone into understanding the venom of this species for several reasons 1) assessing and better treating local snakebites, 2) understanding ontogenetic shifts in rattlesnake venom & diets and 3) understanding the derived changes in venom as the C. durissus/C. simus species complex historically "invaded" the Neotropics south across the Central American landbridge.

Unfortunately, less research has gone into the behaviors and ecology of this species, and previous studies are now presumed invalid in regards to Crotalus simus as they centered around what is now C. durissus and C. tzabcan.