Crotalus adamanteus

The traditional view of rattlesnake taxonomy that recognizes the two monophyletic sister genera Crotalus and Sistrurus (e.g. Brattstrom 1964) has recently been challenged. Stille (1987) and McCranie (1988) presented data that suggested Sistrurus is not monophyletic and rendered Crotalus paraphyletic. Parkinson (1999) found Sistrurus monophyletic but its position rendered Crotalus paraphyletic. Knight et al. (1993) used mtDNA to defend the traditional generic taxonomy, but in order to do so ignored the most parsimonious tree. The genus Crotalus is monophyletic when including the Mexican C. ravus (Murphy et al. 2002), and is supported as such in most recent phylogenies, as well as being the sister taxon to a monophyletic Sistrurus (e.g., Pyron et al. 2013) (Crother 2017).

This species has a limited range in the Southeast where it has undergone an extensive long-term decline due to loss of habitat, heavy exploitation for the skin trade, and general persecution. Although the species persists in much of the range, populations are fragmented and subject to many ongoing threats.

The range encompasses the Coastal Plain of the southeastern United States from North Carolina to south Florida, and west to Mississippi and the Florida parishes of Louisiana, at elevations extending from near sea level to around 500 meters (Mount 1975, Dundee and Rossman 1989, Palmer and Braswell 1995, Ernst and Ernst 2003, Campbell and Lamar 2004). The major stronghold as of 2020 is the northern Florida peninsula, eastern and southern Florida panhandle, and southwestern Georgia (Timmerman and Martin 2003).

North Carolina: restricted to the Lower Coastal Plain south of the Neuse River; formerly occurred in the middle Coastal Plain but apparently never in the North Carolina Fall Line sandhills; not known on North Carolina barrier islands.

South Carolina: patchily distributed in the lower and middle Coastal Plain; common in the coastal marsh-sea island area, occurring on Edisto and three smaller barrier islands.

Georgia: restricted to the Coastal Plain, occurring on the Fall Line sandhills below Columbus (Fort Benning) and thriving on Georgia's sea islands.

Florida: throughout the state, including many of the Florida Keys and most of Florida's east and west coast barrier islands.

Alabama: does not range to the Fall Line but occurs in the lower Coastal Plain where longleaf pine and wiregrass dominated the uplands originally; has been recorded from Dauphin Island.

Mississippi: occurs today principally in the counties of the southeastern portion of the state, east and northeast of the eastern tip of Louisiana; historically may have ranged to the limits of the longleaf pine forest, but today the range has contracted and is confined mainly to the longleaf pine hills and pine flats regions; there are no records from Mississippi barrier islands.

Louisiana: nearly extirpated; was confined to the easternmost three of the seven Florida parishes, and never was reported from Louisiana barrier islands (Means 2017).

As of 2020, state natural heritage programs have records of 388 occurrences with confirmed individuals during the period 2000-2020. Additional occurrences likely are present in Florida (Enge et al. 2016).

The state breakdown is as follows:

Alabama: 3 recent occurrences (2000-2020), 0 historical occurrences (pre-2000 or known to have no surviving subpopulation)
Florida: 152 recent, 244 historical
Georgia: 171 recent, 64 historical
Louisiana: 2 recent, 5 historical
Mississippi: 33 recent, 5 historical
North Carolina: 9 recent, 29 historical
South Carolina: 18 recent, 7 historical

The original range has been reduced and fragmented by agriculture, forestry practices, urbanization, plant succession caused by fire suppression, roadkills, persecution, and commercialization (Martin and Means 2000, Enge et al. 2016, Means 2017).

Current threats to local populations include conversion of native habitat to planted slash or loblolly pine silvicultural plantations, agricultural fields, and urban and suburban uses. Human alteration of native longleaf pine upland ecosystems (including fire suppression) is the most important threat, reducing and fragmenting suitable habitat . Stump removal eliminates underground retreat sites for the snakes.

Roads present a pervasive threat throughout the range, even in conservation areas (Enge et al. 2016). These snakes cross roads regularly and travel slowly, making them particularly susceptible to being struck by cars. Many motorists intentionally run over the snakes when they see them (Enge et al. 2016). Roads also limit the ability of of land managers to perform prescribed burns to maintain suitable habitat. Roads also provide access to rattlesnake habitat to poachers. Besides direct habitat destruction, housing and urban development also prevent the use of prescribed burns.

Another direct threat is the collecting of rattlesnakes for the skin trade and for competition for prizes in rattlesnake roundups held annually in Alabama (1) and Georgia (3). In the past, this activity utilized the practice of gassing the burrows of the gopher tortoise in winter (illegal in Florida and Georgia), sometimes killing rattlesnakes outright, and usually impacting the other fauna inhabiting burrows (Mears 2009). Rattlesnake roundups likely contribute to at least locallized declines (Means 2009). The skin trade may be more damaging. Rangewide, this sort of activity probably accounts for at least ten times (20,000) the number of rattlesnake deaths caused by roundups (Means 2017). Collecting of individuals for the venom trade is also a threat in some areas.

Although this species occurs on coastal barrier islands, it uses upland habitats that are less immediately threatened by sea level rise than species using salt marshes and beaches (Hunter et al. 2015).

In Florida, a snake was found to have the pentastomid parasite Raillietiella orientalis that was likely introduced by invasive Burmese pythons (Python molurus bivittatus; Metcalf et al. 2019). The extent of this threat is unknown. Burmese pythons themselves represent a threat in the Everglades because of competition for prey (Enge et al. 2016). This species is also known to suffer from snake fungal disease (Lorch et al. 2016). Feral hogs are predators of rattlesnakes. Armadillos have expanded into the northern portion of the rattlesnake's range and are introduced in Florida, but they may benefit rattlesnakes by creating burrows needed as refuge sites.