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Eastern Massasauga Rattlesnake

Sistrurus catenatus

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Species Description

The eastern massasauga rattlesnake (EMR) is a small, stout-bodied snake characterized by a heart-shaped head and vertical pupils. Typically reaching lengths of about 0.6 meters (two feet) on average, with a maximum length of around one meter (three feet), EMRs showcase a color palette of gray or light brown, adorned with large chocolate brown to black blotches on their backs and smaller ones on their sides. Notably, populations in specific regions, such as northeast Indiana, southeast Michigan, and northern Ohio, may feature individuals with predominantly black coloration. The belly exhibits marbled dark gray or black patterns, while brown stripes on the head's sides are bordered by narrow white stripes. Their tails, ending in gray-yellow keratinized rattles, sport several dark brown rings. Young EMRs mirror the adults' markings but appear paler, with bright yellow tails that darken with age.

Initially considered a subspecies (Sistrurus catenatus catenatus), recent scientific findings prompted the recognition of the EMR as a distinct species within the genus Sistrurus (Sistrurus catenatus). Phylogenetic analyses and morphological distinctions, coupled with the species' allopatric distributions, corroborate its distinction from the western massasauga rattlesnake (Sistrurus tergeminus) and the desert massasauga rattlesnake (Sistrurus edwardsii). While certain populations in central and northwestern Missouri and southwest Iowa were formerly grouped with the EMR, genetic studies suggest their affiliation with the western and desert massasaugas. As such, the EMR is now recognized as a separate species, distinct from its congeners.


Rautsaw, R.M., Jiménez-Velázquez, G., Hofmann, E.P. et al. VenomMaps: Updated species distribution maps and models for New World pitvipers (Viperidae: Crotalinae). Sci Data 9, 232 (2022).

The known historical range of the eastern massasauga rattlesnake (EMR) encompassed various regions, including sections of western New York, western Pennsylvania, southeastern Ontario, the upper and lower peninsulas of Michigan, the northern two-thirds of Ohio and Indiana, the northern three-quarters of Illinois, the southern half of Wisconsin, extreme southeast Minnesota, east central Missouri, and the eastern third of Iowa. Presently, the boundaries of the EMR's current range generally mirror those of its historical range, although they are patchily distributed. However, the species is likely extirpated from Minnesota. The distribution of existing populations has been constrained by the disappearance of populations across much of the area within these historical boundaries.

In central and western Missouri, populations previously identified as EMR are now genetically linked to the western massasauga rattlesnake (Kubatko et al. 2011; Gibbs et al. 2011). Nonetheless, populations that have persisted in the St. Louis metropolitan area of east central Missouri are believed to be true EMRs (Evans and Gloyd 1948). This determination is primarily based on the physical characteristics of museum specimens, as viable tissues for molecular analysis are unavailable due to the species' extirpation throughout Missouri. Despite this limitation, these populations are included within the historical range of the EMR based on the findings of the Evans and Gloyd study.

Species Status

Habitat loss, driven by various factors, remains the foremost threat to the EMR's survival. This loss encompasses the destruction and modification of diverse native land types, including grasslands, wetlands, forests, and prairies, due to agricultural conversion, urban development, and associated infrastructure such as roads and bridges. For instance, in Illinois, only a minuscule fraction of the once vast prairie habitats remains due to extensive conversion (Ellis 2010). Even protected areas experience habitat modification through processes like vegetative succession, which transforms open habitats crucial for EMR thermoregulation and prey availability into unsuitable dense vegetation areas. Fire suppression exacerbates this issue by allowing woody vegetation to encroach upon EMR habitats, reducing both suitable habitat and prey availability (Kingsbury 2002).


Moreover, habitat fragmentation caused by roads and infrastructure disrupts snake movement, divides populations into smaller fragments, and increases mortality risks due to vehicular traffic and predation (Shepard et al. 2008b). Fluctuations in water levels, resulting from hydrologic alterations like dam construction and water table fluctuations, pose additional threats by affecting hibernation sites and causing stress, displacement, and mortality among EMR populations (Harvey and Weatherhead 2006; Smith 2009; Kingsbury 2002). These cumulative impacts of habitat loss and alteration jeopardize the long-term viability of EMR populations, highlighting the urgent need for conservation efforts to mitigate these threats.

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