The common racer and the several species of whip snakes
(_Masticophis_) were revised by Ortenburger (1928). More recently with
much larger series of specimens, Auffenberg (1955) again revised the
classification of _C. constrictor_, but his study was concentrated in
Florida and neighboring southeastern states with relatively little
attention devoted to populations of the western and central United
States. As the species occurs throughout most of the United States and
south through the coastal lowlands of eastern Mexico to Guatemala, it
is found over a wide range of environmental conditions. Various
characters are subject to geographic variation, and some of them
follow clines that are maintained over extensive areas. Such
characters as the number of hemipenial spines, and the enlargement of
one or more basal spines into hooks, the shape of the premaxillary
bone, the number of maxillary teeth, the numbers of ventrals and
caudals, color of eye, number of dorsal saddle-marks and of ventral
spots in juveniles, and ratios of body proportions including tail
length to total length have been used to characterize the subspecies.
Also important is the shade of coloration of adults. The subspecies
_constrictor_, _priapus_ and _helvigularis_ that are characteristic of
forested habitats in the eastern United States are black dorsally and
have their ventral surfaces suffused to a large extent with dark or
dusky coloring. Farther westward the ground color becomes
progressively paler, greenish, grayish or light brown, and the ventral
surface is yellow (white on the throat and neck). The same tendency
appears in _C. c. paludicola_ of the Everglades. The populations of
arid climates in southern Texas and in the far western states are
relatively pale colored. The species thus conforms to Gloger's Rule in
changing from a pallid coloration in arid climates to a dark pattern
with eumelanins predominating in a humid climate.
Perhaps the most important character that is subject to geographic
variation in the racer, and certainly one of the most neglected, is
body size. With information now available it is not possible to
compare the sizes of different populations except in a general way.
The best sources of information concerning size in several subspecies
other than _flaviventris_, are the publications of Auffenberg (1949
and 1955). Comparison of these data with my own is not entirely
satisfactory because Auffenberg did not indicate clearly differences
in size between the sexes, nor indicate the boundary line between
young and adults. Also, his measurements are of overall length. For
the purpose of comparison I have subtracted 22.5 per cent, an
approximation of ratio of average tail length, from Auffenberg's
figures. He stated (1955:98) that the series of specimens on which
measurements were based were those "with a uniform coloration," that
is to say they had lost the juvenal pattern and were probably sexually
mature. Whether the same statement applied to the large series of
_stejnegerianus_ in the same author's earlier paper (1949:55) is
doubtful.
_C. c. constrictor_: 34 New York specimens averaged 806
millimeters (Auffenberg, 1955:96).
_C. c. flaviventris_: 100 Kansas specimens averaged 791
millimeters (males, 746; females, 836).
_C. c. priapus_: 171 Florida specimens averaged 713
millimeters (Auffenberg, 1955:96).
_C. c. stejnegerianus_: 291 Texas specimens averaged 664
millimeters (Auffenberg, 1949:54).
_C. c. mormon_: 94 West Coast specimens (Museum of Vertebrate
Zoology) averaged 563 millimeters (males 515, females 600).
_C. c. anthicus_: 35 northern Louisiana specimens estimated
to average 582 millimeters (Clark, 1949:249--the author did
not present individual measurements, but indicated the
numbers in several size groups in his sample).
The 100 _flaviventris_ in the above list were recorded in June, July
and August, a season when the young of the preceding year are still
small, and these young were not included. In a fall sample 63 males
averaged 729 millimeters and 65 females averaged 886 millimeters, but
with the nearly grown young (44 males and 40 females) included, the
averages were changed to 651 and 768 respectively. Maximum length
perhaps express differences between the subspecies as well as, or even
better than, the averages listed above. The following figures indicate
some of the maximum overall length measurements in inches that have
been published by various authors. These measurements pertain to
females unless otherwise indicated.
_C. c. constrictor_: 74-3/4, 74-1/4, 73, 65-1/2 (Auffenberg,
1955:96).
_C. c. flaviventris_: 71 (Pope, 1944:172), 72 (Conant,
1958:147).
_C. c. priapus_: 52-1/2 ([M]) (Auffenberg, 1955:98).
_C. c. stejnegerianus_: 37 (Auffenberg, 1949:54), 40 (Conant,
1958:148).
_C. c. mormon_: 51-1/2 (Museum of Vertebrate Zoology).
_C. c. anthicus_: 70 (Conant, 1958:149).
In my own study, the largest racers recorded from the Reservation and
Rockefeller Tract had the following overall lengths: 59, 57-1/4,
55-1/2, 58 [M] (projected from stub tail).
These sets of figures show that compared with the blue racer in
Kansas, with which my own study was concerned, the black racer of the
northeastern states reaches a larger size, while the racers of the
Southeast and especially those of the far West and of southern Texas,
are dwarfed. These size differences are almost certainly correlated
with behavioral and ecological differences among the snakes involved.
Adaptations to exploit certain types of prey and to utilize most
efficiently certain habitats and types of cover, have led to divergent
trends in different parts of the range.