University of Kansas Publications

Museum of Natural History

Volume 13, No. 5, pp. 289-308, 4 figs.

February 10, 1961

Occurrence of the Garter Snake, Thamnophis sirtalis, in the Great Plains and Rocky Mountains

BY

HENRY S. FITCH AND T. PAUL MASLIN

University of Kansas

Lawrence

1961

University of Kansas Publications, Museum of Natural History

Editors: E. Raymond Hall, Chairman, Henry S. Fitch,

Robert W. Wilson

Volume 13, No. 5, pp. 289-308, 4 figs.

Published February 10, 1961

University of Kansas

Lawrence, Kansas

PRINTED IN THE STATE PRINTING PLANT

TOPEKA, KANSAS

1961

Occurrence of the Garter Snake, Thamnophis sirtalis, in the Great Plains and Rocky Mountains

BY

HENRY S. FITCH AND T. PAUL MASLIN

Introduction

The common garter snake (Thamnophis sirtalis) has by far the most extensive geographic range of any North American reptile, covering most of the continental United States from the Atlantic to the Pacific and from south of the Mexican boundary far north into Canada and southeastern Alaska. Of the several recognized subspecies, the eastern T. s. sirtalis has the most extensive range, but that of T. s. parietalis in the region between the Mississippi River and the Rocky Mountains is almost as large. The more western T. s. fitchi occurring from the Oregon and California coasts east through the northern Great Basin, has the third largest range, while the far western subspecies pickeringi, concinnus, infernalis and tetrataenia, and the Texan T. s. annectens all have relatively small ranges.

Since the publication of Ruthven's revision of the genus Thamnophis more than 50 years ago, little attention has been devoted to the study of this widespread and variable species, except in the Pacific Coast states (Van Denburgh, 1918; Fitch, 1941; Fox, 1951). However, Brown (1950) described the new subspecies annectens in eastern Texas, and many local studies have helped to clarify the distribution of the species in the eastern part of the continent and to define the zone of intergradation between the subspecies sirtalis and parietalis. In our study attention has been focused upon parietalis in an attempt to determine its western limits and its relationships to the subspecies that replace it farther west.

Taxonomic History

Thamnophis sirtalis parietalis Say was described (as Coluber parietalis) in 1823 from a specimen obtained in what is now Washington County, Nebraska, on the west side of the Missouri River three miles upstream from the mouth of Boyer's River [Iowa], or approximately eight miles north of Omaha. Although the type locality was unequivocally stated in the original description, Nebraska was not mentioned since the state was not yet in existence. Because the mouth of Boyer's River, the landmark by means of which the type locality is defined, is in Iowa, the impression has been imparted that the type locality itself is in Iowa (Schmidt, 1953:175), and to our knowledge the type locality has never been associated with Nebraska in the literature.

Like all the more western subspecies, parietalis is strikingly different from typical sirtalis in having conspicuous red markings. The relationship between the two was early recognized. Several of the other subspecies were originally described as distinct species. Coluber infernalis Blainville, 1835; Tropidonotus concinnus Hallowell, 1852; Eutainia pickeringi Baird and Girard, 1853; and others now considered synonyms eventually came to be recognized as conspecific with Thamnophis sirtalis. Ruthven (1908:166-173) allocated all western sirtalis to either parietalis or concinnus, the latter including the populations of the northwest coast in Oregon, Washington and British Columbia.

Subsequent more detailed studies by later workers with more abundant material led to the recognition of some subspecies that Ruthven thought invalid and led to the resurrection of some names that he had placed in synonomy. Van Denburgh and Slevin (1918:198) recognized infernalis as the subspecies occurring over most of California and southern Oregon, differing from more northern populations in having more numerous ventrals and caudals and a paler ground color. Fitch (1941:575) revived the name pickeringii for a melanistic population of western Washington and southwestern British Columbia, restricting the name concinnus to a red-headed and melanistic population of northwestern Oregon, and restricting the name infernalis to a pale-colored population in the coastal strip of California.

These changes left most of the populations formerly included in concinnus and infernalis without a name, and Fitch (op. cit.) revived Thamnophis sirtalis tetrataenia (Cope) to apply to them. However, Fox (1951:257) demonstrated that the type of T. s. tetrataenia came from the San Francisco peninsula (rather than from "Pit River, California" as erroneously stated in the original description) and that the name was applicable to a localized peninsular population rather than to the wide-ranging far western subspecies, which he named T. s. fitchi. The range of fitchi includes California west of the Colorado and Mohave deserts (except for the narrow strip of coast occupied by infernalis and tetrataenia), Oregon except the northwestern