_Color Pattern_
Hatchling racers differ much in appearance from adults; whereas the
latter are of dull uniform coloration dorsally, the hatchlings have a
checkered pattern of alternating blotches in several rows, including a
middorsal row, with blotches much larger than those of the other
rows. This basic pattern is perhaps the most common one in all snakes,
and is found in the young of various other genera (notably _Elaphe_)
which lose or alter their markings during development. In these genera
and in the racer, the juvenal checkered pattern may represent
recapitulation of an ancestral condition. The adaptive significance of
having a blotched, checkered pattern in the young, and uniform
coloration in the adult is not evident. I have rarely seen the
hatchlings under natural conditions except by finding them hiding
beneath flat rocks. Their concealing pattern must be fully as
effective as that of adults and the young themselves are more
secretive than the adults.
A hatchling of 240 millimeters snout-vent length was described as
follows on September 22, 1962: Ground color pale olive anteriorly,
gradually darkening posteriorly, marked with chocolate blotches;
middorsal blotches largest averaging about five scales long and seven
or eight scales wide anteriorly; posteriorly, blotches become less
distinct (tending to blend into progressively darkening ground color),
and width-to-length ratio increases; gradual obscuring of blotches
proceeds posteriorly, until on tail they can no longer be
distinguished, and color is uniformly olive; on each side, row of
lateral blotches alternates with that of middorsal blotches; lateral
blotches average somewhat less than two scales long, and approximately
two scales wide and are of irregular shape, sometimes subdivided;
farther down on sides, lower row of lateral blotches alternates with
upper lateral row; this lower lateral row, approximately same size as
upper lateral row, and situated at level of first scale row,
overlapping onto ventrals, where it pales to reddish brown; almost
every ventral scute has one pair or more of dark reddish brown spots,
tending toward semicircular shape, the arc of each projecting forward,
but posteriorly on body these spots become increasingly obscure, and
are indiscernible on posterior end of body and on tail; ventral
surface white on chin and throat, gradually assuming suffusion of pale
greenish gray posteriorly; eye dark with narrow yellowish margin
around pupil; top of head grayish olive, mottled with faint and
irregular dark markings; supralabials whitish, with chocolate
markings, mostly wedge-shaped, in their posterior parts; rostral and
internasals edged with dark posteriorly; posterior upper corner of
loreal and adjacent corner of prefrontal dark; temporals having dark
markings; chin almost immaculate, but with narrow black posterior
edges on some of the infralabials (see Plate 19, Figs. 1 and 2, and
Plate 20, Fig. 2).
The checkered pattern of the juvenile fades gradually as development
proceeds. Persistence of the juvenal markings varies greatly in
individuals and probably is subject to geographic variation also. By
the time sexual maturity is attained the dorsal pattern often is
indiscernible or represented only by faint traces. The ventral
speckling is more persistent.
A female of 602 millimeters snout-vent length in mid-July 1962, at a
probable age of 11 months, was described as follows: Overall dorsal
color olive gray, but with remnants of juvenal pattern discernible;
dark dorsal blotches have almost faded, but their edges, about one
scale wide, are still distinct; low on sides, color fades to pale
bluish gray, and to pale greenish blue on edges of ventrals; on
anterior one-third of body midventral surface is lemon yellow; farther
posteriorly it fades to ivory, almost white on tail; chin white,
except for reddish brown posterior edges of last infralabials, and
streak of same color on each antepenultimate infralabial; top of head
olive gray with irregular scattered dark marks; preoculars pale
centrally with olive brown edges; supralabials white with reddish
brown triangular marks; postnasals white anteriorly, gray posteriorly;
uppermost postocular brownish orange, paler centrally; two rows of
semicircular spots on belly, distinct anteriorly, but fading
posteriorly until indiscernible on posterior part of belly; numerous
small black spots scattered irregularly over dorsal and lateral
surfaces.
A male racer retained more of the juvenal pattern at an approximate
age of 15 months, when he was described on November 30, 1961: Dorsal
surface dark grayish brown, the large juvenal dorsal blotches (each
about eight scales wide) easily discernible, but faint; top of head
dark olive brown, mottled with black, paling in rostral region;
supralabials white on their anterior and lower portions, marked with
brown and blue-gray on their upper and posterior portions; chin white,
but with rusty markings on last four infralabials; ventrals
ivory-yellow with rusty spots of which the largest are approximately
three-fourths of the ventrals' breadth; first row of scales bluish
gray, or with greenish suffusion (in neck), most of scales having
indistinct dark spots; second row of scales similarly colored but more
suffused with dusky pigment, blending into the darker duller color of
the dorsal surface.
A female of 720 millimeters snout-vent length, presumably about 20
months old, but not gravid, on June 13, 1962, was described as
follows: Juvenal pattern no longer clearly discernible but scattered
traces of it remain; dorsal color predominantly grayish olive, with
occasional small black spots in streaks scattered irregularly over
dorsal and lateral surfaces; at anterior end of body lateral scales
have bluish green edges but this shading becomes less noticeable
posteriorly; head mostly olive dorsally with marking obscure;
parietals have a large faint blotch; supralabials retain faint dark,
brownish markings on their upper parts; dark spot on median edge of
each prefrontal; supraoculars slightly darker than adjacent scutes;
chin mostly white, with yellowish suffusion at edges of scales;
ventral surface predominantly yellow, but fading to grayish white
posteriorly; remnants of juvenal ventral spots faintly discernible as
tan or whitish areas on yellow ventrals.
Munro (1950b:124) mentioned a blue racer of 749 millimeters total
length (hence probably having a snout-vent length of 600 millimeters,
or a little less), which retained faint juvenal markings when caught
on June 23, 1948, even though it was sexually mature, since it laid
eggs on the night of July 4, 1948. During several weeks of captivity
this snake's markings faded perceptibly.
In fully adult blue racers, those more than three years old, the
juvenal markings have become completely obliterated. In those from the
area of my study, the dorsal coloration is subject to much individual
variation, typically olive brown, but ranging from pale bluish gray to
dark brown, dark blue, or slaty. In most, the dorsal color is uniform,
but in some there are streaks and isolated scales of black. The dark
dorsal color extends down the sides onto the lateral corners of the
ventrals and the subcaudals. The chin is white but the remainder of
the ventral surface is ivory colored.
_Bodily Proportions_
The slender and streamlined bodily proportions of the racer are
subject to change through allometric growth. The head, and especially
the eyes, are relatively large in the hatchling, and become relatively
smaller as growth proceeds. The relative tail length seemingly
increases in the growing young and then decreases slightly in adults.
Snout-vent length and tail length were recorded in almost all the
racers examined, but other measurements were recorded in relatively
few. In many racers, especially the larger adults, tails had been
damaged and lacked their terminal parts. Often only the tip was
missing, but, of course, such individuals were not usable in the study
of proportions of the tail. Table 2 summarizes information concerning
relative tail length in 935 racers of both sexes and various sizes,
from northeastern Kansas. Nearly all measurements are from the live
snakes; a few are from recently killed individuals.
In hatchlings, the proportions of the tail are not noticeably
different in males and females, but data indicate that the snakes'
tails are approximately seven per cent longer in males than in
females; as growth proceeds, the tails become relatively longer in
proportion to the body, in both sexes. The ratio reaches its maximum
in young adults, having increased from approximately 28 per cent of
the snout-vent length in males and 26 per cent in females, to 31 per
cent in males and a little more than 28 per cent in females. In the
largest racers, of both sexes, these percentages are slightly reduced.
Tail-length is subject to a fairly wide range of individual variation,
which tends to obscure the trends determined by sex and size.
Table 2. Relative Tail Length in Male and Female Racers of Different
Size Groups
=============+============================+============================
| Males | Females
Snout-Vent +--------+-------------------+--------+-------------------
Length in | Number | Mean ratio of | Number | Mean ratio of
Millimeters | of | tail-length to | of | tail-length to
| racers | snout-vent length | racers | snout-vent length
-------------+--------+-------------------+--------+-------------------
150-200 | 7 | 27.3 ± .833 | 2 | 26.3
201-250 | 24 | 27.8 ± .490 | 23 | 25.9 ± .479
251-300 | 9 | 28.8 ± .634 | 4 | 26.6
301-350 | 20 | 29.8 ± .246 | 11 | 25.0 ± 1.060
351-400 | 8 | 28.8 ± .530 | 12 | 27.5 ± .404
401-450 | 6 | 27.8 ± .775 | 5 | 26.3 ± .357
451-500 | 12 | 29.7 ± .434 | 6 | 26.8 ± .858
501-550 | 45 | 30.5 ± .283 | 15 | 27.6 ± .284
551-600 | 76 | 31.0 ± .218 | 35 | 27.1 ± .254
601-650 | 45 | 29.6 ± .313 | 64 | 27.8 ± .163
651-700 | 50 | 30.5 ± .241 | 36 | 27.1 ± .350
701-750 | 72 | 30.5 ± .177 | 45 | 27.6 ± .373
751-800 | 45 | 30.3 ± .373 | 38 | 27.8 ± .325
801-850 | 48 | 29.7 ± .274 | 50 | 27.5 ± .205
851-900 | 18 | 29.1 ± .519 | 35 | 28.6 ± .422
901-950 | 5 | 29.8 ± .672 | 31 | 26.7 ± .252
951-1000 | 1 | 29.5 | 19 | 26.9 ± .390
1001-1050 | .... | ..... | 15 | 25.9 ± .413
1051-1100 | .... | ..... | 6 | 26.4 ± .725
1101-1150 | .... | ..... | 1 | 28.5
1151-1200 | .... | ..... | 1 | 25.0
-------------+--------+-------------------+--------+-------------------
In 88 racers caught in the summer of 1962 the following measurements
were recorded: Head length, from tip of snout to angle of jaw; maximum
head width; greatest diameter of eye; circumference of neck;
circumference at mid-body; circumference at posterior end of body;
and circumference of tail-base. Because the measurements were small,
and were made in the field on active, struggling snakes, a high degree
of precision could not be attained, and the range of error was several
per cent, with occasional relatively large errors. Nevertheless,
ontogenetic trends are clearly indicated. Most of the racers measured
were adults of small to medium size--in the range 500 to 799
millimeters, snout-vent length. Twelve females and seven males ranged
from 800 to 1035 millimeters, and seven young (all females) were less
than 500 millimeters. In measurements other than circumference of
tail-base, significant differences could not be found between males
and females of the same size group; therefore the sexes were combined
to obtain larger series.
Table 3. Bodily Proportions (Expressed as Ratio of Snout-vent Length)
in Racers of Different Sizes
==========================+===============+===============+==============
| Large | Medium | Small
Size Group |(more than 800 | (500 to 800 |(less than 500
| millimeters) | millimeters) | millimeters)
--------------------------+---------------+---------------+--------------
Length of head | 3.61 ± .036 | 3.82 ± .025 | 5.39
Width of head | 1.93 ± .049 | 2.02 ± .023 | 2.53
Diameter of eye | .56 ± .008 | .63 ± .009 | 1.00
Circumference of neck | 4.71 ± .082 | 5.05 ± .052 | 6.64
Circumference at mid-body | 7.11 ± .238 | 7.66 ± .082 | 8.58
Circumference at posterior| | |
end of body | 5.06 ± .113 | 5.03 ± .061 | 5.90
Circumference of tail | 4.23 ± .113[1]| 4.22 ± .075[1]| 4.66[1]
at base | 4.47 ± .171[2]| 4.66 ± .043[2]|
--------------------------+---------------+---------------+--------------
[1] Females.
[2] Males.
Table 3 shows that as compared with adults, the small young racers
have stouter, stubbier bodies, relatively large heads, and,
especially, large eyes. Allometric growth seems to continue throughout
life and the changed proportions of the adults are accentuated in the
largest and oldest individuals.
_Lepidosis_
Scalation that of typical colubrid (see Pl. 19); rostral large,
extending back onto dorsal surface of snout, bluntly pointed behind;
paired internasals considerably wider than long, convex anteriorly,
almost straight-edged posteriorly, each extends laterally to naris;
paired prefontals approximately twice size of internasals, and wider
than long, extending laterally on each side to level of nostril;
frontal convex anteriorly, concave on each side, bluntly pointed
behind, nearly twice as wide anteriorly as posteriorly; parietals
large; angle formed between them by frontal slightly more than 90
degrees; nostril large, situated between almost equal sized anterior
nasal and posterior nasal plates; loreal slightly smaller than nasals,
its anterior edge inclined forward superiorly; two rows of temporals
on each side; in upper row, first one narrow and elongate, second much
shortened, third intermediate in shape; in lower row all three
approximately alike in size and shape; two postoculars, the lower
larger; seven supralabials, first small and low, longer along upper
edge than along lower, second slightly longer than high, third higher
than long, contacting eye; fourth largest, contacting posterior part
of eye, and lower postocular; fifth nearly as large, pointed above;
sixth also large, pentagonal; seventh low and rectangular; on chin
first pair of infralabials separate mental from anterior genials;
second infralabial minute; third approximately twice its size; fourth
much smaller, rhomboidal, fifth also large, pentagonal; sixth smaller,
rhomboidal, bluntly pointed behind; seventh smaller, narrow behind;
eighth small and elongate; second pair of genials longer and narrower
than those of first pairs, separated from each other by smaller
scales; genials in approximately five rows, but somewhat irregular in
arrangement, mostly smaller and narrower than body scales; latter all
smooth, arranged in 17 rows for about two-thirds of body length, then,
by loss of third row on each side, reduced to 15; scales of neck
region rounded and relatively small, one-third to one-fourth size of
larger body scales; lowest scale row on each side largest with its
scales much wider and less symmetrical than others; most of body
scales of approximately hexagonal shape; on forebody they average
approximately twice as long as wide, but farther posteriorly on body,
width-length ratio gradually increases and some of scales, notably
those of lowest row, approximately as wide as long; regularity of
scale rows broken on sides just above vent by presence of many small
additional scales; on tail scale rows drop out posteriorly in rapid
succession, until on posterior third only four are present; ventrals
strongly convex posteriorly, with free posterior edges, nearly half
length of scales; anal plate divided, with diagonal suture; subcaudals
in double series, those of right and left sides alternating; several
minute subcaudal-like scales on each side of vent.
_Dentition_
In the racer the maxillary, palatine, pterygoid, and dentary bones
bear teeth (Fig. 1). The teeth are all much alike in size and shape,
small, sharp, and recurved, typically at an angle of approximately 50
degrees. The number of teeth present is variable. Because the teeth
are small and loosely attached to the jaw bones, and often are broken
off in the capture and ingestion of prey, each bone usually lacks part
of its complement of teeth. Even the sockets vary somewhat in number
between individuals, and between the left and right sides in some
snakes. Most of the skulls that I examined were not thoroughly
cleaned, and the adherent dried tissues made it difficult to obtain
accurate counts of the sockets. In ten skulls from Kansas and
Nebraska, most frequently occurring numbers of sockets for each of the
dentigerous bones were: maxillary, 15; palatine, 11; pterygoid, 18;
dentary, 18.
[Illustration: Fig. 1. Lateral view of right side of skull of adult
female blue racer, × 4. University of Kansas Museum of Natural History
no. 18305, from Greenwood County, Kansas.]
_Hemipenis_
Penial characters have proven to be useful in the classification of
snakes, providing bases for separating subfamilies, genera, and
species. In the racer even the subspecies have trenchant penial
characters by which they may be separated in some instances. The
hemipenis is roughly cylindrical, but widest at the base (Fig. 2). The
sulcus spermaticus is unbranched. Approximately the basal one-third of
the hemipenis has a smooth surface, broken only by the sulcus
spermaticus and by three greatly enlarged spines, which form
hooks--one anterior, one posterior, and one dorsal. The dorsal hook is
the largest of the three. Distal to the smooth part is a zone of small
spines, each recurved and mounted on a fleshy tubercle. The zone of
spines is poorly developed on the anterior side and is interrupted on
the posterior side in the vicinity of the sulcus spermaticus but is
best developed on the posterior side a short distance above and below
the sulcus spermaticus. The spines are arranged in several oblique
rows. Those of the proximal row are best developed, and there is rapid
diminution in the size of those situated farther distally.
Approximately the distal two fifths of the hemipenis forms a third
zone, lacking distinct spines, but having numerous deep longitudinal
grooves, alternating with lamellae which have fimbriated edges, and
which fuse with each other and divide to form a reticulated pattern.
[Illustration: Fig. 2. Lateral view of injected and everted left
hemipenis (slightly enlarged) of a blue racer from the Rockefeller
Tract, Jefferson County, Kansas, showing heavy spines at base of
organ, small spines of central zone and lamellae of terminal part.
This hemipenis is not fully engorged.]