_Sexual Behavior_
Many observers have published accounts of the courtship and/or mating
of the racer, but all of these are, to some degree, incomplete.
Because of the widely different circumstances, and the different
viewpoints of the observers involved, the several accounts give much
different impressions of sexual behavior in this species. Either
singly or combined, the published accounts do not provide an adequate
description of the process.
My own observations, made both under natural conditions and in large
outdoor enclosures, are likewise somewhat incomplete, but indicate
that the whole sequence of courtship and mating is divisible into the
following well-defined stages: 1) the finding of a receptive female by
the male; 2) the persistent following of the female by the male, who
courts her by lying extended along her body and performing writhing
movements, with periodic interruptions during which he momentarily
leaves the female and courses rapidly through the grass around her; 3)
the acceptance of the male by the female, signalled by the raising of
her tail and the almost instantaneous intromission; 4) the dragging of
the passive male by the female while he is firmly attached to her
during the period of coitus; 5) separation of the pair and involution
of the male's hemipenis.
Even in the breeding season, racers that were confined in enclosures
usually were either indifferent to each other or responded with
reactions of fear or hostility. In moving they tended to follow the
edges, and often two moving in opposite directions would approach each
other; when this occurred, one snake might strike at the other with a
short jab that seemed to be mostly bluff, and then would dart away.
The males, being smaller, were usually the more wary.
Sexual behavior was noticed on only a few occasions. Several large
adult males were less wary than others and usually manifested
curiosity or interest toward other racers. My most complete
observations of sexual behavior were made on May 18, 1962, when a
newly caught adult male was added to an enclosure of 100-foot
circumference already containing several racers, two of which were
large adult females. Within half an hour the male was found courting
one of the females. She was lying in a loose coil, with the male
extended along her. At my approach the female darted away in alarm for
approximately three feet, and the male moved with her, so swiftly and
adroitly that he maintained contact and was in approximately his
original position with respect to the female when she stopped.
Spasmodic rippling movements passed down the body of the male as he
lay in contact with the female. These movements lasted several
seconds, increasing in intensity, alternating with longer periods of
little or no movement. As each period of vigorous writhing reached its
climax, the male's head jerked forward and backward several times in
seeming excitement. The female's behavior was mostly passive. She
seemed to be receptive, but from time to time, without any noticeable
warning, she darted away for several feet as she had when the pair was
first discovered. Each time the male darted forward with her,
maintaining contact while she moved. These swift movements of the
female seemed to be spontaneous, at least in most instances there was
no evident cause for alarm. The female's movements seemed to stimulate
the male's interest rather than to discourage him. In most instances
the female moved only four to five feet, then stopped abruptly or
turned back. She would stop in a loose resting coil, in thick grass,
with the male lying over her. Often she coiled in such a way that the
posterior end of her body was beneath her forebody, but this did not
seem to deter the male from moving the posterior end of his body into
position beside hers. After a sudden change in the female's position,
the rear of the male's body would perform groping movements along that
of the female until his cloacal region was approximately opposite
hers. The male sometimes had his chin pressed against the female's
back, especially when he was moving forward along her, but more often
his head was raised, and frequently was as much as 18 inches from the
female's head.
At intervals averaging approximately ten minutes, during a little more
than an hour of observation, the male would suddenly dart away from
the female, and with unusually rapid and animated movements, he would
move around her in an irregular and devious course, sometimes as far
as five feet away, but usually within 18 inches. Usually on each such
expedition several or many circuits were made; then the male would
return to the female and would glide rapidly along her until he
attained the mating position. A period of especially vigorous courting
movements would follow.
At 12:55 p. m. it was necessary for me to discontinue observations,
and I left the female confined in a cloth bag. Returning at 1:20 p. m.
I found that the male was not displaying interest in the female
confined in the bag, nor in the other female loose in the enclosure.
The first female was released from the bag, and was out of sight for
approximately four minutes. When relocated she was again attended by
the male, who was carrying on courtship even more vigorously than he
had before. At 1:35 p. m. the male achieved intromission. Although the
pair was under observation at the time intromission occurred, the
actual eversion of the hemipenis was not seen because the snakes were
partly concealed by dense vegetation. There was a sudden flurry of
movement, the male's head waving and his body thrashing. In an instant
these violent movements subsided, and after a few seconds the female
began to crawl forward slowly. The male had relaxed, and relinquished
his contact with the female anteriorly. As she moved away he was
dragged after her tail-first. He made slight backward wriggling
movements that perhaps aided in maintaining sexual contact. The
female's restlessness increased, and in eight minutes she dragged the
male in a circuitous course a distance estimated to be between 20 and
30 feet. At 1:40 p. m. the pair was ten feet from the point where
copulation had begun. The female showed increasing inclination to
climb, raising her head and forebody against the trunks of saplings,
and finally reaching up one to a branch 20 inches above the ground,
and climbing first along the branch and then farther up the main
trunk. As she progressed the male was lifted from the ground,
dangling limply suspended by his hemipenis and its base had become
exposed. At 1:43 p. m. separation occurred and the male dropped into
the grass. Semen dripped from the cloacae of both snakes. That from
the female was tinged with blood. The individuals involved in this
observation were kept in the enclosure subsequently but no further
sexual behavior was noted.
Contrary to the popular belief that these racers have permanent mates,
all available evidence indicates that they are promiscuous, and two or
more males may simultaneously court the same female in the brief
spring breeding season. On May 24, 1960, while I was walking in a
hilltop field of brome grass, a sudden movement attracted my attention
to three racers lying alongside each other. Only the posterior parts
of their bodies and their tails were visible. Two were males and were
performing the characteristic slow writhing movements against the body
of the female from either side. Although the heads were not in view,
the snakes may have been able to see me through the screening
vegetation; after I had watched for approximately 20 seconds, all
three suddenly took alarm, for no apparent cause, and scattered.
Further evidence of promiscuity is provided by the account of Ellicott
(1880:207) who wrote regarding the eastern subspecies: "I noticed a
ball of black snakes (_Bascanion constrictor_ L) rolling slowly down a
steep and stony hillside ... about two miles above Union Factory,
Baltimore County, Md. ... kept together by procreative impulses." It
was stated that this observation was made in early spring. "Snake
balls" have often been observed, and described in the literature;
usually the snakes involved were garter snakes (_Thamnophis_) or water
snakes (_Natrix_). Seemingly, typical aggregations consist of a single
adult female and several or many males attempting to mate with her.
There is a distinct possibility that the snakes involved in Ellicott's
observations were misidentified.
Sexual behavior of the racer is in most respects remarkably similar to
that of the common garter snake, _Thamnophis sirtalis_, well known
through the work of Blanchard and Blanchard (1942). In studying sexual
behavior of racers, several observers have failed to differentiate
between the different stages of the mating process, and have assumed
that copulation was occurring when actually only the precopulatory
behavior was observed. In an early description of courtship in this
racer in Kansas, Brons (1882:365) stated that the female "at times,
seems to toy with the male, indisposed to yield to his importunities,
though pressed with ardor. To avoid his suit, at times, she will dart
through grass, among stones, or enter a crevice. Should he be able to
reach his mate while within a hole, he is not slow in bringing her to
the surface, again to be repulsed. Upon an unbroken ground the sexual
union is less prolonged. Here she is unable to free herself from his
quick and effectively directed moves. In case she attempts to quit
him, a coil is thrown about her body, and his head laid flat upon her
neck, and replaced as promptly as dislodged, evidently in the endeavor
to propitiate her."
Another account probably based on courtship rather than copulation is
that of Wright and Wright (1957:135), who described the behavior of a
pair of _C. c. priapus_ on Billy Island, Okefinokee Swamp in southern
Georgia, on May 8, 1921, as follows: "They were stretched out, more or
less coiled ... the rear parts of the bodies from the vent were
entwined. The female, or smaller one seemed to have its tail around
that of the male. There were contortions or quiverings from time to
time.... May 8, 1921: Jackson Lee saw black snakes entwined, the male
seizing the female by the top of the neck."
Blanchard and Blanchard (_op. cit._) have described the dragging of
the male by the female during coitus in the garter snake, and the
temporarily inseparable bond formed between members of a pair by the
recurved spines of the engorged hemipenis, but it has not been
generally recognized that the process is much the same in other
colubrines. Cottam (1937:229) described and photographed mating in a
pair of _C. c. mormon_ in Utah. The copulating racers were shown in a
loose coil lying alongside each other with tails intertwined. However,
when disturbed by the observers, these racers made frantic efforts to
escape, crawling in a spiral course, while remaining attached and
intertwined, "with no evident attempt to separate" during
approximately a quarter hour of observation.
The racer is notorious for its aggressive behavior and occasional
alleged attacks on humans in the breeding season. The tendency has
doubtless been much exaggerated, especially in the verbal second- or
third-hand accounts based on the alleged observations of
eye-witnesses. Nevertheless, the supposition that large adults will
sometimes pursue or attack humans when disturbed is well
substantiated. In most of the instances known to me, it is the large
eastern subspecies, _C. c. constrictor_, involved in these incidents,
and seemingly the smaller racers of the Middle West, far West and
South are less inclined to behave aggressively. In May 1958 two pairs
of large racers were confined in a semicircular wire enclosure thirty
feet across and open on top, and with natural vegetation, at the
Reservation headquarters. Often in approaching the cage I saw two or
more racers in close association, but because of sheltering
vegetation, and the snakes' timidity observation was difficult. On May
19 a pair were lying partly extended in loose coils, but immediately
the female took alarm and darted away, breaking loose from the male;
his hemipenis was exposed, and underwent involution and retraction in
approximately 30 seconds. Unlike the female, the male on this occasion
did not attempt to escape, but turned to face me with a show of
aggressiveness. Probably copulation was in its final stages when the
disturbance occurred.
Circling of the female racer by the male from time to time in the
course of courtship has not been recognized by previous observers as a
part of the mating pattern, but Pope (1944:171) described somewhat
analogous behavior, probably modified by unnatural conditions of
captivity and the crowding of many racers in one cage. Pope, citing
earlier observations by Noble, wrote: "When sexually excited, the male
blacksnakes dash wildly about before paying court to individual
females. In captivity these dashes excite all specimens confined
together. A male, after picking out a mate, moves his chin lightly
along her back, while undulations run forward along his sides and he
extends his tongue now and then. Later he throws the part of his body
near his vent over the corresponding part of the female, the two tails
sometimes becoming loosely intertwined."
Recorded dates of mating for the species are all in spring, but
indicate a span of many weeks for the breeding season, and this spread
results in part from geographical differences. Published records are
as follows:
Subspecies _constrictor_
May 12, 1930, in Ohio (Conant, 1938:55)
Subspecies _priapus_
May 8, 1921, in Georgia (Wright and Wright, 1957:135)
May 9, 1921, in Georgia (Wright and Wright, 1957:135)
Subspecies _flaviventris_
May 3, 1931 (two pairs) in Missouri (Boyer and Heinze, 1934:195)
April 18, 1936, in Missouri (Anderson, 1942:210)
May 12, 1928, in Kansas (Gloyd, 1928:123)
Subspecies _mormon_
June 10, 1927, in Utah (Cottam, 1937:229)
July 7, 1938, in California (Cunningham, 1959:17)
In the course of my live-trapping, I occasionally found more than one
racer in a trap. As might be expected from the low yield per trap,
such double or multiple captures were relatively rare. Chance, and
unusually strategic placement of certain traps were doubtless
contributing factors. May and October, being the most productive
months for trapping, yielded a high proportion of these combined
captures. Some involved an adult and an immature snake, or two adults
of the same sex. Eliminating all these, there remain 44 heterosexual
captures of adults. These latter captures are significantly
concentrated in their seasonal distribution and indicate a spring
breeding season; 34 were in May, six were in June and four were in
October. Eight of the May records and one June record each involved a
trio of snakes--two males and a female in every instance. Distribution
of the spring records, grouped in five-day intervals, was as follows:
May 11 to May 15: 14 June 5 to June 9: 0
May 16 to May 20: 5 June 10 to June 14: 2
May 21 to May 25: 8 June 15 to June 19: 2
May 26 to May 30: 13 June 20 to June 24: 0
May 31 to June 4: 1 June 25 to June 30: 1
Approximately 87 per cent of the records fell in the twenty-day
interval, May 11 to 30, which is regarded as the main breeding season.
Presumably males continue to be at the peak of breeding condition and
continue to search for females after the latter have become
unreceptive, partly explaining the scattering of records through most
of June.
Several of the females found in traps with males in May had abundant
active sperm in their cloacae and oviducts and probably had been
inseminated within a few hours of the time they were checked. Others
lacked sperm, but the cramped quarters inside the traps may have
effectively prevented the consummation of courtship, especially when
two males were confined with the same female. None of the females
trapped with males in October was found to be inseminated, and it
seems doubtful whether copulation ever occurs at that time of year,
although males have motile sperm and seem to be in breeding condition
then.
_Cycle of the Male_
Cloacal smears indicate that males mature sexually and first produce
sperm in August and September when they are a little more than a year
old. Insofar as could be determined, there was no sexual activity at
this time of year, and actual breeding of the adolescent racers was
postponed until the following May. By this time at an average age of
20 months, the snakes had made further growth.
[Illustration: Fig. 16. Catches, in semi-monthly periods, of racers in
their summer habitats, at Harvey County Park (upper) and at
Reservation and Rockefeller Tract (lower). Intensive activity in
spring (the breeding season), tapering off rapidly as the season
advances, is well shown by the larger sample, but in the years of
trapping at Harvey County Park operations usually were not fully
underway until the latter part of May.]
Mr. Dwight R. Platt studied the changes in the male reproductive
organs during the annual cycle at Harvey County. In racers recently
emerged from hibernation he found the seminiferous tubules filled with
Sertoli syncytium, but containing few germ cells. Spermatogonia
proliferate in May and June. During the first half of July primary
spermatocytes are the dominant cells in the seminiferous tubules. By
early August spermatids are dominant and the first free spermatozoa
are present. In late October spermiogenesis is essentially complete
and the tubules are relatively empty before the snakes hibernate.
During the season of activity the seminiferous tubules increase to
approximately double their minimum diameter, reaching the maximum in
August. Cyclic changes in size and secretory activity of the ductus
deferens, ductus epididymis, and sexual segment of the renal tubules
occur, with maximum size and secretory activity coinciding with the
time of movement and storage of the spermatozoa. The latter are stored
in both ductus deferens and ductus epididymis. Despite the short
breeding season, a male racer has active sperm at all seasons.
_Eggs_
In accounts of the racer in the humid southeastern United States,
Brimley (1903:261), Wright and Bishop (1915:160) and Tinkle (1959:195)
mentioned the ease with which the eggs might be found and the
superficial situations in which they were sometimes deposited. Both
Wright and Bishop, and Tinkle made field studies in swamps, where
presumably the subsoil was saturated with moisture and too wet for the
eggs. Tinkle mentioned finding one clutch beneath a discarded
newspaper and another beneath a small, thin board. Surface (1906:167)
stated that in Pennsylvania the eggs were to be found in loose soil,
in sawdust piles, or in decaying wood of hollow logs or trees. Clark
(1949:249) stated that in northern Louisiana the eggs are laid in
soft, moist soil such as may be found beside decaying logs. Minton
(1944:457) found two clutches under flat stones on hillsides in
Indiana. In the more arid climates of the far western states the
species' habits are much different in this regard. Through many years
of familiarity with _C. c. mormon_, I have never seen its eggs.
Presumably nests in this part of the range are deep underground, most
often in old burrows of the pocket gopher (_Thomomys_), which are so
abundant that in many areas the soil is riddled with them. Burrows of
the ground squirrels (_Spermophilus_ sp.) and other small digging
mammals also provide potential insulated nest sites with the favorably
moderate temperatures and high humidities that the eggs of snakes
require.
On the morning of July 10, 1962, I was directed to the sites of two
clutches recently plowed up, 1-1/2 miles north of the Reservation (Pl.
21, Fig. 2). The eggs were in a fallow field having a stand of
sunflowers three to five feet high. The plow blades turned the soil at
a depth of approximately seven inches. In each instance only a few
eggs were visible. They were well scattered in the loose soil turned
up by the plow; 21 were found in one clutch and 10 in the other. All
the eggs were intact except two that had minute punctures from which
liquid oozed. Seemingly the eggs _in situ_ had been well above the
level of the blade--at depths of four to five inches. No nest
cavities were discernible where the eggs were found, but elsewhere in
the field tunnels of moles (_Scalopus aquaticus_) and prairie voles
(_Microtus ochrogaster_) were exposed by the plow. Presumably the eggs
had been in such tunnels, which had disappeared as the loose soil
crumbled. Another clutch was discovered in an adjoining field on July
16. The nine eggs were at depths ranging from 6-1/2 to nine inches,
and only the two topmost eggs had been turned up by the plow. All
three clutches were within a few feet of the edges of the fields.
On the Reservation and nearby areas I have seen remains of an
estimated 20 clutches that have been destroyed by predators. The
remains in every instance consisted of an excavation, and the strewn
torn and empty eggshells. Nests were at depths of four to eight inches
in old tunnels, which most often seemed to be those of moles but also
included some of the prairie vole, and perhaps some of the pine vole
(_Microtus pinetorum_). All these nests were in open sunny places in
prairie or pasture habitat.
Table 7. Numbers and Sizes of Eggs in Clutches of the Blue Racer From
Eastern Kansas
========+===============+=================+==============+==============
Number | | | | Snout-vent
of | Lengths | Widths | Weights | length of
Eggs | (mm.) | (mm.) | (grams) | female (mm.)
--------+---------------+-----------------+--------------+--------------
17 | 26.5(29-24) | 17.0(19.0-16.5) | 5.5(6.0-4.4) | 892
8 | 33.3(39-31) | 16.3(17.5-14.0) | 6.0(6.7-5.6) | 899
12 | 29.1(32-25.5) | 17.1(18.5-16.0) | 4.9(5.2-4.4) | 773
14 | 26.9(30-24) | 19.2(20-18) | 5.2(6.2-4.4) | 772
10 | 31.7(33-29) | 16.5(18-15) | 6.0(6.5-5.6) | 807
11 | 29.7(33-27) | 16.7(18-15) | 5.4(5.8-5.0) | 858
21 | 28.9(32-27) | 18.4(19.5-18) | 5.9(6.3-5.6) | 1038
13 | 30.7(34-28) | 19.3(20-18) | 6.8(7.5-6.1) | 907
18 | 29.0(30-26) | 17.9(19-16) | 4.9(5.5-4.3) | 911
12 | 30.3(34-28) | 17.8(19-15) | 5.2(6.1-3.8) | 843
14 | 30.9(36-29) | 19.4(21-18) | 6.8(7.6-6.2) | 846
--------+---------------+-----------------+--------------+--------------
Many observers have described the eggs of the racer, which are white,
elliptical, somewhat elongate, with tough, leathery, somewhat
flexible, shells, and a granular surface. Like other snake eggs, those
of the racer gradually absorb moisture during incubation. They become
more turgid and increase in weight and dimensions, especially in
breadth, and by the time of hatching are nearly twice their size at
laying. Between different clutches and even within the same clutch
there is notable variation in the size of the newly laid eggs. Munro
(1948:199) noted that in a small adult racer kept by him, the eggs
laid were larger but less numerous than those produced by a large
adult. Munro noted also that shape of eggs in the two clutches
differed; the smaller snake produced more elongate eggs of smaller
diameter. The idea that eggs laid by the smaller females are more
slender and elongate is not supported by my own data. For 11 clutches
of eggs examined soon after laying, dimensions, weights, and the
lengths of the females are shown in Table 7.
In a clutch of eggs beginning to hatch on September 3, 1958,
dimensions and weights were as follows: length 31.8 (36-30), diameter
22.0 (24-21), weight 9.7 (10.3-9.3).
Gravid females that were kept in captivity in anticipation of their
laying usually produced their clutches within a few days. The laying
dates of such individuals are shown in the following list. Those with
asterisks were from the Harvey County study area, others were from the
Reservation and Rockefeller Tract.
June 19, 1961 July 1, 1961 July 12, 1961
June 21, 1959 July 4-5, 1962* July 15, 1961*
June 23, 1961* July 6, 1955 July 18, 1961*
June 26, 1959 July 7, 1959* July 20, 1961
June 29-30, 1962* July 7, 1959* August 8, 1960*
A further indication of the period when laying occurs was provided by
the appearance of females gravid and progressively more swollen with
eggs, then their abrupt disappearance and replacement by thin and
wrinkled individuals that obviously were recently parturient. The
following records show the course of these events on the Reservation
in the years when summer trapping was done with sufficient
consistency. These dates provide a rough approximation of the time
when laying occurs locally. They indicate a laying season concentrated
in a period of approximately three weeks in this locality. Records
from published literature also indicate that laying occurs in late
June and early July at the latitude of Kansas, but somewhat earlier in
the southern United States.
Table 8. Dates When Parturient and Gravid Racers were Captured on
Reservation and Rockefeller Tract in Several Years, Indicating Time
of Oviposition
========================+=========+=========+=========+=========+========
Year | 1958 | 1959 | 1960 | 1961 | 1962
------------------------+---------+---------+---------+---------+--------
First parturient female | June 18 | June 17 | June 22 | June 20 | June 13
Last gravid female | July 8 | July 11 | July 5 | July 12 | July 16
------------------------+---------+---------+---------+---------+--------
Many authors have made statements regarding the size of the clutch in
the racer, on the basis of those found in the field, those laid after
capture, or those dissected from gravid females. Some of the
statements were based upon small but unspecified samples, and are far
from the mark. From records accumulated in the course of my own field
work, and a summarization of those in published accounts a substantial
sample is available showing the usual size of clutch in the area of my
study, and the trends of geographic variation in some parts of the
range.
_C. constrictor_ (all combined)
151 clutches averaged 10.61 (2 to 31) eggs.
_C. c. constrictor_ 14 clutches averaged 16.80 (7 to 31) eggs.
_C. c. priapus_ 11 clutches averaged 12.60 (7 to 21) eggs.
_C. c. mormon_ 43 clutches averaged 5.79 (2 to 13) eggs.
_C. c. flaviventris_ 82 clutches averaged 11.78 (5 to 26) eggs.
_C. c. stejnegerianus_, one clutch contained 10 eggs.
In the foregoing list the sample of _C. c. flaviventris_ may be
divided as follows:
Reservation and vicinity: 36 clutches averaged 11.65 (6 to 21) eggs.
Harvey County study area: 21 clutches averaged 12.0 (5 to 18) eggs.
Museum specimens from Kansas: five clutches averaged 9.2 (6 to 14)
eggs.
Published records (Kansas, Indiana, Iowa, Louisiana, Missouri,
Oklahoma, Texas): 20 clutches averaged 12.5 (5 to 22) eggs.
Table 9. Published Records Indicating Dates of Laying in Different
Populations of Coluber constrictor
===============+==================+============+=========================
Date | | |
of Laying | Subspecies | Area | Authority
---------------+------------------+------------+-------------------------
June 9, 1952 | _flaviventris_ | SE Texas | Guidry (1953:50)
July 1-2, 1920 | _flaviventris_ | Texas | Ortenburger (1928:183)
June 1, 1920 | _flaviventris_ | Texas | Ortenburger (1928:183)
June 9, 1926 | _flaviventris_ | Oklahoma | Force (1930:31)
June 24, 1926 | _flaviventris_ | Oklahoma | Force (1930:31)
July 19, 1928 | _flaviventris_ | Oklahoma | Force (1930:31)
July 16 | _flaviventris_ | Oklahoma | Carpenter (1958:114)
July 4-5, 1948 | _flaviventris_ | Kansas | Munro (1948:199)
July 4, 1948 | _flaviventris_ | Kansas | Munro (1948:199)
June 26, 1930 | _flaviventris_ | Ohio | Conant (1938:55)
July 3, 1961 | _mormon_ | NW Oregon | Van de Velde, Martan
| | | and Risley (1962:212)
June 7, 1957 | _priapus_ | S Illinois | Rossman (1960:219)
June 19, 1912 | _priapus_ | S Georgia | Wright and Bishop
| | | (1915:160)
July 10, 1940 | _priapus_ | S Illinois | Cagle (1942:187)
July 6 | _constrictor_ | New York | Ditmars (1907:284)
June 27-July | _constrictor_ | Virginia | Werler and McCallion
5, 1951 | | | (1951:251)
June 5, 1947 | _stejnegerianus_ | S Texas | Auffenberg (1949:54)
---------------+------------------+------------+-------------------------
Published records of clutches laid by racers, from which figures used
in the foregoing account were obtained, include the following:
_C. c. constrictor_: 22 (Barbour, 1950:104); 21, 13 (Brimley,
1903:261); 25 (Conant, 1938:55); 8 (Ditmars, 1907:284); 7,
12, 14, 16, 19, 20, 31 (McCauley, 1945:76); 14 (Wright and
Wright, 1957:136).
_C. c. flaviventris_: 7 (Anderson, 1942:210); 22 (Brumwell,
1951:205); 11 (Carpenter, 1958:114); 8, 9, 9 (Force,
1930:31); 10 (Guidry, 1953:50); 18 (Liner, 1949:230); 5, 8,
17 (Marr, 1944:484); 5, 14 (Munro, 1948:199); 13, 19
(Ortenburger, 1928:183); 6, 15 (Tinkle, 1959:195); 15, 19
(Wright and Wright, 1957:141).
_C. c. priapus_: 20, 21 (Cagle, 1942:187); 7 (Conant,
1938:55); 19 (Rossman, 1960:219); 5, 9, 11, 14 (Wright and
Bishop, 1915:160); 16 (Wright and Wright, 1957:147).
_C. c. mormon_: 13, 9, 8, 5, 5, 5, 4, 4 (Cunningham,
1959:17); 5, 6 (Stebbins, 1954:374); 6 (Van de Velde,
Martan and Risley, 1962:212); 3, 6 (Wright and Wright,
1957:144):
_C. c. stejnegerianus_: 10 (Auffenberg, 1949:54).
In general, the number of eggs in the clutch is proportional to the
size of the female producing them. The larger and bulkier females
produce more eggs. Geographic trends in number of eggs produced are
perhaps controlled by differences in size between different
populations; thus, the large eastern _constrictor_ produces nearly
three times as many eggs per clutch as does the small western
_mormon_, whereas the centrally located _flaviventris_ is somewhat
intermediate in size and in numbers of eggs produced.
In most reptiles growth in length and bulk continues after attainment
of sexual maturity. For many kinds including _Eumeces fasciatus_,
_Crotaphytus collaris_, _Cnemidophorus sexlineatus_, _Agkistrodon
contortrix_ (Fitch, 1954:60; 1956:236; 1958:36; 1960:174), and
_Sceloporus olivaceus_ (Blair, 1960:94), it has been shown that the
larger and older females in a population produce more offspring than
do the smaller and younger individuals. This situation applies in the
racer, as shown by the clutches of 52 females correlated with their
sizes and presumed ages (Fig. 17, Table 10). The two-year-olds
contribute a relatively small quota to the annual brood, partly
because their clutches are small, but more especially because many of
them fail to attain sexual maturity in time to breed. Many of the
female racers that are more than two years old also fail to produce an
annual clutch of eggs. The 24-day period May 28 to June 20 inclusive
is judged to comprise the period when eggs have generally enlarged
sufficiently to be detected in gravid females, but still have not been
laid in most instances. In this period, in 1960, 1961 and 1962, ratios
of gravid females to those not detectably gravid in several supposed
age groups arbitrarily established on the basis of size, were as
follows:
Two-year-olds 2 gravid, 13 apparently not gravid
Three-year-olds 5 gravid, 4 apparently not gravid
Four-year-olds 3 gravid, 2 apparently not gravid
Five-year-olds 4 gravid, 3 apparently not gravid
Six-year-olds (or older) 8 gravid, 2 apparently not gravid
[Illustration: Fig. 17. Graph showing number of eggs per clutch, and
correlation with supposed age (as deduced from length of body) in
female blue racers from the Reservation, Rockefeller Tract, and Harvey
County Park.]
From the appearance of these snakes it is reasonably certain that none
had already laid eggs when it was recorded, but there is some
possibility that a few individuals not noticeably gravid at the times
they were examined, produced eggs subsequently. However, these meager
data do seem to indicate that most of the two-year-old females and a
minority of older individuals fail to produce clutches in the annual
breeding season.
Table 10. Fecundity of Female Racers in Various Age-size Classes,
All From the Reservation and Rockefeller Tract
========================+===========+=====================+==============
Most Probable Age | Number of | Snout-vent length | Number
in Years of Females | females | of females; average | of eggs in
(as indicated by size) | in sample | and extremes | clutch
------------------------+-----------+---------------------+--------------
2 | 10 | 688 (589-748) | 9.2 (6-12)
3 | 19 | 789 (756-840) | 9.9 (5-14)
4 | 7 | 856 (850-861) | 10.8 (8-12)
5 | 6 | 907 (892-933) | 13.0 (8-17)
6 or more | 10 | 1005 (955-1088) | 15.7 (11-19)
------------------------+-----------+---------------------+--------------
Under unfavorable conditions eggs can be resorbed, but probably this
can occur only if initiated before ovulation. A racer in which six
small eggs were palped on June 28, 1960, was kept until July 23 but
did not oviposit. It no longer appeared gravid and the ova could not
be detected by palpation. Another female had 13 eggs on June 21, 1960,
but by July 23 when the snake was released the eggs had not been laid
and no longer could be detected. Both snakes refused to feed
throughout their confinement.
Like other reptilian eggs, those of the racer are dependent upon the
warmth of their surroundings for incubation. They are tolerant of a
wide range of environmental temperatures, but the higher the
temperature the more rapidly incubation proceeds. Under natural
conditions there may be much difference in hatching time in two
clutches laid at the same time and in the same locality. Site of the
nest--deep and well insulated, or shallow; in a well shaded situation
or one exposed to maximum amounts of sunshine--would largely control
rates of development. Clark (1949:249) writing of the subspecies
_anthicus_ in north-central Louisiana, stated: "eggs are laid about
the first of June.... young begin to make their appearance at about
... July 1." Even for the southern states these dates of laying and
hatching seem somewhat too early to reconcile with the records
published by other observers, and are in need of verification,
especially since they seem to be based upon vaguely remembered
observations rather than upon written records. At the other extreme
Surface (1906:167) wrote of _constrictor_ in Pennsylvania that
hatching may occur as late as October, and that there is evidence some
young may even remain in the egg over winter before hatching occurs.
Several incubation periods are on record for clutches laid and hatched
in captivity, as follows:
_C. c. mormon_, Oregon, 47 and 51 days (laid July 3, 1961,
hatched August 19 and 23; Van de Velde, Martan and Risley,
1962:212).
_C. c. stejnegerianus_, Texas, 73 days (laid June 5, 1947,
hatched August 17, Auffenberg, 1949:54).
_C. c. priapus_, S. Illinois, 58 and 59 days (laid July 10,
1940, hatched September 6 and 7, Cagle, 1942:187).
_C. c. flaviventris_, Kansas, 50 days (laid July 4 and 5,
hatched August 23 and 24; Munro, 1950:124).
_C. c. flaviventris_, Texas, 43 days (laid June 9, 1952,
hatched July 22; Guidry, 1953:50).
No incubation periods for eggs in natural nests have been recorded. In
the course of my study, eggs obtained from 12 captive females were
hatched in confinement, with an average incubation period of 51 days
(43 to 63) as follows:
Laid July 6, 1955, hatched August 20.
Laid July 3, 1958, hatched September 3 and 4.
Laid June 21, 1959, hatched August 17.
Laid June 26, 1959, hatched August 17.
Laid July 7, 1959, hatched August 23 to 25.*
Laid June 23, 1960, hatched August 20.*
Laid June 30, 1961, hatched August 30.
Laid July 15, 1961, hatched September 1 and 2.*
Laid July 18, 1961, hatched September 2 and 3.*
Laid July 4 and 5, 1962, hatched August 15 and 16.*
Laid June 29 and 30, 1962, hatched August 14 and 15.*
Laid July 6, 1962, hatched August 16 to 20.*
In the foregoing list those entries marked with asterisks were
obtained from the Harvey County study area; all others were from the
Reservation and Rockefeller Tract.
_Hatching_
Detailed observations on hatching were made on a clutch of eggs laid
on June 29 and 30, 1962, by a female caught in Harvey County. The
first egg in the clutch had already been laid in the trap when the
female was found at 11:30 a. m., June 29. Two of the eggs were
abnormal, with thin transparent shells, and were found to lack embryos
when they were opened on July 7. Later, two other eggs were attacked
by mold and the embryos died early in development. The clutch was kept
in a can of slightly damp soil. At 2:30 p. m. on August 13, when the
clutch was examined, egg no. 6 was found to have hatched. The young
snake had made a 21-millimeter slit in the shell. At 12:50 a. m. on
August 14, it was discovered that eggs 1, 4, 5 and 7 each had been
slit. No. 4 had two parallel slits separated by a two-millimeter strip
of shell, and the young racer could be seen inside. At 1:05 a. m.
this young snake had changed position and was lying upside down in the
egg, his snout protruding slightly through one of the slits. At 1:45
a. m. he was again right side up, still in the shell. At this time
each of the slit eggs showed the protruding snout of a young snake.
Occasionally the viscous liquid egg white would be blown into a large
bubble on the surface of the shell as the young snake exhaled. A third
slit, parallel to the others, had appeared in egg no. 4. A hatchling
emerged from egg no. 1 between 2:20 and 3:20 a. m., and another from
no. 7 between 7:00 and 9:00 a. m. The hatchling struck vigorously many
times, and vibrated his tail when he was disturbed. Egg no. 3 was
first slit between 7:00 and 9:00 a. m., and three more slits appeared
in it between 9:15 and 10:15 a. m. At 12:45 p. m. a hatchling was
found in the act of emerging from egg no. 4, and approximately the
anterior one-fourth of its body protruded. Disturbed by the movements
of the observer, the little snake drew back into its shell. This
hatchling began to emerge again at 12:50 and his hatching was
completed at 1:00 p. m. Between 5:40 and 6:20 p. m. a hatchling
emerged from egg no. 3 (for several hours this hatchling had been
lying on its back inside the egg, with only its snout protruding); two
slits appeared in egg no. 2 and three slits appeared in egg no. 8. At
6:50 p. m. the hatchling in the latter thrust his snout through the
slit in this eggshell. This hatchling was lying on its back at first
but by 10:50 it had shifted to a normal position. It emerged from the
shell between 2:35 and 2:50 a. m. Egg no. 2 was the last to hatch. At
7:05 p. m. the hatchling inside made two additional small slits in the
shell, and at 7:30 p. m. thrust its snout through one of them, while
lying on its back. At 1:45 a. m. it was right side up, but at 3:00 a.
m. had reverted to its previous position. At 4:40 a. m. it was again
right side up, and it emerged from the shell at 5:55 p. m.
On August 17, at 11:00 a. m., hatchlings no. 5 and no. 6 had lost
their egg teeth. All others still had their egg teeth then, but by
10:00 p. m. that of no. 8 was missing, and that of no. 4 was loose and
dropped out while the snake was being handled. On August 20 at 9:00 a.
m., hatchling no. 7 had lost its egg tooth; nos. 2 and 3 retained
theirs only in part, and no. 1 had its egg tooth intact. By noon on
August 22 no trace of an egg tooth remained on any of the hatchlings.
In the same group of hatchlings sign of impending molt was first
noticed on the morning of August 17, when no. 6 was noted to have its
eyes clouded and milky in appearance. By evening no. 1 had attained
the same stage and no. 7 was beginning to show it. On the morning of
August 20, shedding had begun in no. 6, while no. 2 and no. 8 had
milky eyes. The eyes had cleared in no. 1 and no. 7, and were still
clear in the remaining hatchlings. On August 22 shedding had been
completed by no. 1 and no. 8, and all others were in the process of
shedding.
Another clutch of 14 eggs from a recently captured female was found
freshly laid in a cage on July 6, 1962. Hatching of 13 occurred August
16 to 20, as shown in Table 11.
Table 11. Times of Hatching in a Clutch of Racer Eggs From Harvey
County Park
========+================================+=============================
| Time at which shell | Time that hatchling
Number | was slit by hatchling | emerged
of Egg +---------+----------------------+---------+-------------------
| Day | Hour | Day | Hour
--------+---------+----------------------+---------+-------------------
1 | Aug. 17 | 10:50 a. m. | Aug. 18 | 3:00 to 6:00 p. m.
2 | Aug. 17 | 12:15 to 12:50 p. m. | Aug. 18 | 3:25 to 4:25 p. m.
3 | Aug. 17 | 1:40 p. m. | Aug. 17 | 10:45 p. m.
4 | Aug. 18 | 3:00 to 6:00 p. m. | Aug. 19 | before 7:00 a. m.
5 | Aug. 16 | 10:45 a. m. | Aug. 17 | 6:30 to 7:55 a. m.
6 | Aug. 17 | 9:00 a. m. | Aug. 18 | 6:30 to 7:30 a. m.
7 | Aug. 17 | 4:15 p. m. | Aug. 20 | 1:00 to 7:00 a. m.
8 | Aug. 17 | 3:40 p. m. | Aug. 18 | 5:00 to 6:00 p. m.
9 | Aug. 17 | 7:30 p. m. | Aug. 18 | 6:30 to 7:30 a. m.
10 | Aug. 16 | 10:48 a. m. | Aug. 17 | 11:05 a. m.
12 | ? | no record | Aug. 18 | 6:00 to 6:30 a. m.
13 | Aug. 17 | 8:00 to 8:20 a. m. | Aug. 17 | 5:30 to 5:50 p. m.
--------+---------+----------------------+---------+-------------------