Trimorphodon lambda

Based on mtDNA data (Devitt 2006) and patterns of morphological variation, Devitt et al. (2008) recognized 6 species in the Trimorphodon biscutatus species complex: T. lyrophanes, T. lambda, and T. vilkinsonii in the United States and Mexico, and T. biscutatus, T. paucimaculatus, and T. quadruplex occurring to the south in Mexico/Central America.

Trimorphodon lambda hybridizes with T. vilkinsonii in extreme southeastern Arizona (Cochise County) and southwestern New Mexico (Grant and Hidalgo counties) (Devitt et al. 2008). This species may also come into contact with T. lyrophanes in southeastern California and/or extreme southern Nevada, and with T. paucimaculatus near the Sonora-Sinaloa border (Devitt et al. 2008). Specimens from contact zones may be difficult to identify (Devitt et al. 2008).

Range extends from southern Nevada (Nye County) and extreme southwestern Utah (Washington County) south through much of Arizona (except for the northeastern quarter), southwestern New Mexico (Hidalgo and Grant counties), southeastern California (generally east of the Salton Trough region), Sonora, western Chihuahua (west of the Sierra Madre Occidental) to northern Sinaloa (Devitt et al. 2008).

The number of distinct occurrences has not been determined using consistent criteria, but the species is represented by a fairly large number of collection sites and locations (as defined by IUCN). Secretive habits and occurrence in rough terrain that is difficult to survey effectively make it likely that this snake occurs in substantially more localities than are presently known.

No major threats have been identified. Locally, in a few places where roads pass through optimal habitat, excessive collection for the pet trade likely has caused a reduction in abundance. This species inhabits rough terrain that often is not suitable for various kinds of land development.