Lampropeltis triangulum

Following SSAR (Nicholson 2025), as currently defined, L. triangulum comprises populations of the former subspecies L. t. triangulum, L. t. syspila (part), and L. t. amaura (part). Burbrink et al. (2022) found using genome-scale data with detailed phylogeographic and hybrid-zone analyses, along with ecological niche-modeling analyses, that L. triangulum has a zone of hybridization (6% of the combined range) with L. gentilis that occurs primarily where the eastern Nearctic forests transition to the grasslands of the Great Plains but otherwise remains distinct throughout its range. This work also indicates that both L. triangulum and L. gentilis may hybridize with L. elapsoides specifically in a contact zone in Louisiana but that all three also remain distinct outside of that zone. In contrast, Chambers and Hillis (2020) and Chambers et al. (2023) argue that the hybridization detected between L. triangulum and L. gentilis renders these taxa as synonymous and thus all Nearctic milksnakes, excluding L. elapsoides, should be considered L. triangulum. However, Chambers et al. (2023) also found the same two lineages corresponding to L. gentilis and L. triangulum, with the same area of connection as that inferred by Ruane et al. (2014) and Burbrink et al. (2022). See Burbrink et al. (2024) for reanalyses and evaluation of Chambers et al. (2023) demonstrating species status.

Ruane et al. (2014) recognized seven distinct species previously considered to be L. triangulum: L. triangulum, L. gentilis, L. elapsoides, L. annulata, L. polyzona, L. abnorma, and L. micropholis.

The correct year of publication of the original description is 1789 (not 1788 as commonly cited).

Range extends from southern Minnesota, Michigan, southern Ontario, southern Quebec, and southern Maine southward to North Carolina and extreme northern Alabama and Georgia; also Mississippi, possibly Arkansas north of the Arkansas, and northeastern Louisiana (specifically La Salle Parish) (Ruane et al. 2014). The range meets that of L. elapsoides in the southeastern United States.

This species is represented by a very large number of occurrences (subpopulations) and locations (asdefined by IUCN).

Intensive agricultural development and urbanization have caused localized declines, and collectors probably have depleted accessible populations near roads, but in most areas this snake is not threatened by these factors. This species is vulnerable to snake fungal disease, but the scope, severity, and population impact of this disease on L. triangulum are unknown.