E. A. McIlhenny (1872-1949), of Avery Island, Louisiana, near New Iberia, was an avocational naturalist who was one of rattlesnake expert Laurence M. Klauber's most prolific correspondents, especially concerning the southeastern species, with which Klauber had little personal field experience. McIlhenny is quoted or mentioned a total of ten times in Klauber's classic two-volume treatise Rattlesnakes (1956, 1972, 1997). McIlhenny was an experienced outdoorsman and conservationist who contributed to the academic literature, especially concerning birds and reptiles. He was also an accomplished popular author on natural history subjects in the same disciplines. In herpetology he is best known for his book The Alligator's Life History (1935), which is still occasionally cited today. Most of McIlhenny's observations apparently occurred in the late 1800s or early 1900s.
Consequently, it seems unlikely that he would have made a misstatement or misidentification in his several correspondences with Klauber when he referred to the Eastern Diamondback Rattlesnake (Crotalus adamanteus) as occurring at Avery Island. Avery Island is about fifty miles west of the Mississippi River, which is traditionally considered the western boundary of sorts to much of the southeastern Austroriparian fauna. It is in reality a salt dome elevated somewhat above the neighboring lowlands rather than an actual island surrounded by water. Because of their relative elevation, however, these salt domes tend to support a vegetational regime more resembling eastern forests than the surrounding coastal lowlands.
Historically favorable open canopy habitat favorable for Crotalus adamanteus in Louisiana (after Martin and Means 1999). Locality of Avery Island indicated.
There are two specific mentions of alleged Eastern Diamondbacks at Avery Island by McIlhenny in Klauber's book. The first, on page 455, recounts that in 1911 on Prospect Hill [a portion of Avery Island], McIlhenny observed a large "Diamondback Rattlesnake (Crotalus adamanteus)" coiled 10-12 feet above the ground in a wax myrtle tree and immediately under a wood rat nest. As this statement is within an account of arboreal activity by various species of rattlesnakes, Klauber did not comment on the unusual locality.
Later, on page 524, in a discussion of "Island Habitats," Klauber says that McIlhenny informed him that the Pygmy Rattlesnake (Sistrurus miliarius), the Timber Rattlesnake (Crotalus horridus), and the Eastern Diamondback Rattlesnake (Crotalus adamanteus) had all been found at Avery Island. Klauber's only comment was ". . . although adamanteus may now be exterminated there." Klauber's introduction to this section indicates that he was aware that Avery Island wasn't actually an island in the traditional sense. McIlhenny also associated the release of fifty head of free-ranging hogs with the virtual disappearance of rattlesnakes on Avery Island within two years.
Additionally, on page 857, in a discussion of immunity to other snakes' venom, McIlhenny refers to having captives of both Crotalus horridus and C. adamanteus occasionally bite each other without suffering ill effects. He does not state, however, whether the C. adamanteus specimens were locally obtained.
Klauber also refers to Beyer's (1900) contention that the decline of Crotalus adamanteus in eastern Louisiana could be attributed to the extensive practices of clear cutting forests and draining of swamps, causing him (Klauber) to speculate that the species may have already been exterminated in eastern Louisiana at that time (1956). Despite apparently accepting McIlhenny's accounts of C. adamanteus in the Avery Island area, west of both the Mississippi River and the Atchafalaya Basin, Klauber's range map for this species includes only extreme eastern Louisiana. Beyer (op. cit.) also mentions a record of C. adamanteus from the east bank of the Mississippi River but this was discounted by Dundee and Rossman (1989), who declared it "somewhat dubious".
Although not mentioning the McIlhenny allegations in their extensive review of the distribution of the Eastern Diamondback, Martin and Means (1999) stated:
"We believe that the ranges of C. adamanteus and C. atrox probably met at some time during the Pleistocene. Not only might their northern range limits have oscillated in response to climatic changes but the contact zone between the two species probably shifted east and west repeatedly. During humid climatic periods the range of C. adamanteus probably extended westward across the Mississippi River but during dry periods its range contracted eastward. Then C. adamanteus may have been completely displaced by C. atrox west of the Mississippi. Post-Pleistocene back-filling of the Mississippi River Valley and subsequent widening of the delta and the establishment of unbroken swamp and bottomland habitats may have prevented re-establishment of C. adamanteus west of the Mississippi. North-south range adjustments probably occurred as the glaciers advanced and retreated. During colder periods the northern limits of C. adamanteus were probably south of the present limits and a large amount of the exposed continental shelf may have been occupied by this snake."
If Martin and Means' conclusions are true, it could very well mean that McIlhenny was actually observing a relict population of C. adamanteus at Avery Island in the late 1800s and early 1900s.
Beyer, G. E. 1900. Louisiana herpetology. Proc. Louisiana Soc. Naturalists 1897-1899: 25-46.
Dundee, H. A. and D. A. Rossman. 1989. The Amphibians and Reptiles of Louisiana. Louisiana State University Press, Baton Rouge, LA.
Klauber, L. M. 1956. Rattlesnakes, their habits, life histories, and influence on mankind. 2 vols. Berkeley: University of California Press.
____________. 1972. Rattlesnakes, their habits, life histories, and influence on mankind. 2 vols. Second edition. Berkeley: University of California Press.
____________. 1997. Rattlesnakes, their habits, life histories, and influence on mankind. 2 vols. Second edition. Foreword by H. W. Greene. Berkeley: University of California Press.
Martin, W. H. and D. B. Means. 1999. Distribution and Habitat Relationships of the Eastern Diamondback Rattlesnake (Crotalus adamanteus). Herpetol. Nat. Hist. 7(1): 9-34.