Natural History of the Racer Coluber constrictor

Chapter III: Part 3

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Lizards figure prominently in most of the food samples, but only a few species, those that live on or near the ground in grassy places, have been recorded. Most of the records pertain to scaly lizards (_Sceloporus undulatus_ and _S. graciosus_), earless lizards (mainly or entirely _Holbrookia maculata_), racerunners (_Cnemidophorus sexlineatus_) and skinks (_Lygosoma laterale_ and _Eumeces_ sp.).

Snakes are important in the racer's food in most parts of the range, but the large racers of the Northeast are those most inclined to ophiphagous habits. The common garter snake (_Thamnophis sirtalis_) is the species most commonly eaten. Probably this is a matter of availability rather than preference, since the garter snake is one of the commonest and most widely distributed of North American snakes, occurring throughout most of the racer's range. The green snakes (_Opheodrys_) also are represented frequently. The other snakes eaten are mostly medium-sized to small colubrids, of a variety of kinds. However, there are three records (from Connecticut, Missouri and Kansas) of the racer preying on the venomous copperhead. There are many records of the racer preying on smaller individuals of its own species. In my own records racer remains appeared 18 times, equalling in frequency those of the common garter snake and exceeding all other kinds. In four of these instances the scale remains were relatively few and the scales were relatively large, suggesting as an alternative to actual predation that a racer may have eaten part of its own sloughed skin, or that patches of shed skin may have adhered to the scat after its deposition in the trap. However, in the remaining 14 instances the remains of racer found in scats clearly indicated cannibalism, since the scales found were small and numerous and often were associated with bone. Cannibalism seems to occur frequently enough to be a significant factor in the reduction of the first year young. Liner (1949:230) described two instances of cannibalism in a litter of blue racers hatched in captivity. In one instance two young had seized the same lizard, and one having swallowed the lizard, continued to engulf the other snake, although it was of a size approximately equal to that of the first snake. Nevertheless, swallowing was completed, with the snake eaten pressed in a series of curves. A second instance of cannibalism occurred when one young racer attempting to catch a lizard struck another racer by mistake, then retained its hold and commenced swallowing. A similar instance was observed in a brood that I kept in 1962 after hatching had occurred in the laboratory.

Hatchling turtles of two kinds (_Chrysemys picta_, _Terrapene carolina_) have been reported in the racer's food. Probably other kinds are eaten also. However, the awkward shape and almost inflexible shell of the prey on the one hand, and the slender form of the racer, with limited distensibility of the gullet on the other, would limit this type of predation to occasional instances involving an unusually large racer and a small turtle.

There seem to be no records of the racer preying on salamanders. Many kinds of frogs are eaten, chiefly ranids and hylids, and the leopard frog (_Rana pipiens_) is the most frequent victim. Wright and Bishop (1915:160) stated that the toad (_Bufo terrestris_) occupied first place in the racer's food in the region of Okefinokee Swamp, Georgia, but they mentioned no specific instances of this species being eaten. Klimstra (_loc. cit._) found only four toads in his large sample of digestive tracts from Illinois. Because of their virulent dermal secretions, bufonid toads are avoided by many kinds of snakes and predation on them by the racer probably is unusual.

Most authors who have written concerning the food habits of the racer have mentioned insects as part of the diet. Statements in the literature have often seemed to imply that the racer feeds on insects in general, according to their availability. However, the large number of records now available demonstrate that the racer is highly selective in choice of its insect food, that soft-bodied orthopterans, chiefly crickets, grasshoppers and katydids, are the usual insect prey, with occasional predation on moths and their larvae. Eating of other insects such as cicadas and June beetles, is a rarity, but on occasion a racer may be tempted to sample such prey when it finds the newly emerged imago before its exoskeleton has hardened. I am convinced that such rarely occurring items as carabid beetles, hemipterans, homopterans, diplopods and spiders are secondary prey items, eaten by frogs that later were eaten by the snakes, in most instances if not in all. It is noteworthy that several of the same genera of grasshoppers and crickets are prominent in the food samples collected in widely separated parts of the racer's range.

As might have been anticipated, different species of prey were not utilized by the racers to the same extent throughout the snakes' season of activity. Grasshoppers, for instance, fluctuated from a low of 25.3 per cent (frequency) in the May sample to a high of 41.4 per cent in the September sample. Availability of prey, rather than any change of preference on the part of the racer, explains this trend. Thus, the locust, _Arphia simplex_, which, unlike most local grasshoppers, overwinters in the adult stage, is most prominent in the food in May, represented by 15.7 per cent, but it decreases progressively to a low of 1.8 per cent in September. The common grasshoppers of the genus _Melanoplus_ show just the opposite trend, increasing during the summer, from a low of 2.62 per cent in May (when all are nymphs and most are too small to constitute a meal worthy of a racer's attention) to a high of 31.5 per cent in September. Mammals are best represented in the food in May, when they collectively comprise nearly 30 per cent of the items taken, and they are progressively less well represented as the summer advances. Both _Microtus_ and _Peromyscus_ conform to this trend, but the relative numbers of _Peromyscus_ rise again abruptly in October. The general trend may be explained by the fact that in May most small mammal populations have a high proportion of young of the year, and these young are especially vulnerable to predation by the snakes. Also, insects in general are less available in spring, and this may force the racers to utilize vertebrates to a greater extent than at other seasons. Actually, the seasonal changes in food sources are not especially striking, and it seems that each important prey species is utilized more or less throughout the season of the racer's activity.

Table 5. Distribution by Months of Various Categories of Prey Items
Recorded From Blue Racers From Kansas, Chiefly From the Reservation
and Rockefeller Tract

=======================+======+======+======+======+=======+======
| May | June | July | Aug. | Sept. | Oct.
-----------------------+------+------+------+------+-------+------
Cricket (233) | .17 | .37 | .28 | .01 | .05 | .12
_Ceuthophilus_ (94) | .01 | .19 | .30 | .14 | .13 | .23
Katydid (96) | .03 | .06 | .08 | .25 | .15 | .43
_Melanoplus_ (188) | .03 | .12 | .27 | .15 | .19 | .24
All grasshopper (388) | .15 | .17 | .21 | .16 | .12 | .19
_Microtus_ (79) | .45 | .32 | .13 | .02 | .07 | .01
_Peromyscus_ (39) | .41 | .18 | .08 | .08 | .05 | .20
All mammal (162) | .41 | .25 | .14 | .03 | .05 | .12
Lizard (70) | .07 | .46 | .29 | .15 | .01 | .02
Snake (61) | .37 | .18 | .08 | .13 | .09 | .15
_Arphia_ (72) | .50 | .25 | .12 | .04 | .03 | .06
-----------------------+------+------+------+------+-------+------

Table 6. Distribution of Various Common Prey Animals in a Sample of
625 Among Racers of Different Size Groups

====================+====================================================
| Snout-Vent Length (mm.) of Racers in Sample
Kinds of prey and +-----+-----+-----+-----+-----+-----+-----+-----+----
their percentage | 200 | 300 | 400 | 500 | 600 | 700 | 800 | 900 |1000
frequencies in | to | to | to | to | to | to | to | to | to
in samples | 299 | 399 | 499 | 599 | 699 | 799 | 899 | 999 |1099
--------------------+-----+-----+-----+-----+-----+-----+-----+-----+----
gryllid cricket | .40 | .39 | .11 | .25 | .23 | .15 | .15 | .12 | .08
| | | | | | | | |
_Melanoplus_ | | .09 | .14 | .14 | .14 | .15 | .20 | .27 | .25
| | | | | | | | |
_Ceuthophilus_ | .20 | | .11 | .13 | .06 | .07 | .12 | .09 | .04
| | | | | | | | |
_Orchelimum_ | | | | .04 | .02 | .01 | .01 | .01 |
| | | | | | | | |
tettigoniid | | | .03 | .02 | .06 | .03 | .02 | .05 |
| | | | | | | | |
"other grasshopper" | | | | | | | | |
and miscellaneous | | | | | | | | |
orthopteran | | .30 | .25 | .10 | .09 | .03 | .12 | .07 | .09
| | | | | | | | |
_Arphia simplex_ | | | .03 | .02 | .05 | .08 | .08 | .04 | .09
| | | | | | | | |
miscellaneous insect| | .04 | .04 | .09 | .07 | .04 | .08 | .05 | .04
| | | | | | | | |
lizard | .20 | .09 | .18 | .09 | .07 | .11 | .01 | .01 |
| | | | | | | | |
snake | .20 | | .07 | .06 | .05 | .04 | .05 | .08 | .12
| | | | | | | | |
_Microtus_ | | | .04 | .02 | .08 | .13 | .09 | .12 | .25
| | | | | | | | |
_Peromyscus_ | | .09 | | .02 | .05 | .06 | .03 | .05 | .04
| | | | | | | | |
"other mammal" | | | | .01 | .04 | .10 | .03 | .03 |
| | | | | | | | |
bird | | | | | | | .01 | .01 |
+-----+-----+-----+-----+-----+-----+-----+-----+----
Total prey items| | | | | | | | |
for size group| 5 | 23 | 28 | 101 | 120 | 121 | 127 | 76 | 24
--------------------+-----+-----+-----+-----+-----+-----+-----+-----+----

The wide disparity in size between young and adult racers also results in utilization of different food sources to some extent. In some kinds of snakes adults and young draw their food from entirely different sources, but in the racer there is broad overlap, as shown in Table 6. The samples from the largest and smallest size groups of racers are relatively small. Two important kinds of prey--voles and grasshoppers of the genus _Melanoplus_--were not found at all in the smallest size groups of snakes and comprised increasing percentages in the food of the larger size groups. A large adult vole is too large to be swallowed except by an unusually large racer, and a young vole old enough to leave its nest is far too large for a hatchling racer. Grasshoppers of the genus _Melanoplus_ are relatively large and heavily armored, and so are relatively immune to attacks from the smaller snakes. Small soft-bodied orthopterans including _Gryllus_, _Ceuthophilus_ and _Orchelimum_, and also lizards and snakes, are best represented in the food of the smaller racers. Other types of prey showed no definite correlation with size of the racer taking them.

Reproduction

_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.

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

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

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

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.
--------+---------+----------------------+---------+-------------------

Growth

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Natural History of the Racer Coluber constrictorChapter III: Part 3

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