Part 7

Food of the "buttermilk snake" (C. c. anthicus) is known only through Clark's study (1949:249). In an unstated number of examinations he found "mice" in 25, "rats" in five, lizards (Sceloporus undulatus and perhaps others) in eight, frogs (Rana pipiens) in seven, and birds in three.

The food of C. c. stejnegerianus is known only from the work of Auffenberg (1949) but his sample was based on 206 racers that had food, among the total of 291 recorded. Unfortunately, he did not present actual numbers of the various prey animals, but divided the food into seven categories and listed these as percentages. He did not indicate whether the percentages represented volumes or numbers of individual occurrences, and evidently there was some error in computation since his combined percentages totalled 111. The categories and their percentages were as follows: grasshoppers, 42.5; crickets, 13.5; miscellaneous insects, .6; earless lizards (Holbrookia sp.), 40.1; scaly lizards (Sceloporus sp.) 2.1; frogs (Rana sp.) 10.0; rodents, 2.2. Auffenberg divided his sample of racers into five size classes, and showed that the smaller snakes fed chiefly on insects whereas vertebrates were increasingly prominent in the food of the larger snakes.

The food of C. c. mormon is known chiefly through the work of Ortenburger (1928:228) who cited instances of a skink (Eumeces skiltonianus) and a young garter snake (Thamnophis sirtalis) being eaten, and listed the following items from 24 stomachs that he examined: 7 decticids, 8 acridids, 5 oedipines, 1 tryxaline, 6 Melanoplus sp., 3 M. mexicanus, 2 M. devastator, 1 M. bivittatus, 2 Dissosteira carolina, 1 Chortophaga viridis, 3 Neduba carinata, 3 Trimerotropus sp., 7 Hippiscus sp., 2 Steiroxys sp., 3 Canoula pellucida, 2 Stenopelmatus fuscus, 2 S. pictus, 4 Gryllus assimilis, 4 Ceuthophilus sp., 1 Pristoceuthophilus pacificus, 6 Gammarotettix bilobatus and 2 cicada nymphs. Grinnell, Dixon and Linsdale (1930:149) found that one of these racers had eaten a cricket. Fitch (1936:644) found another in the act of swallowing an adult vole (Microtus californicus), and recorded (1935:18) that two alligator lizards (Gerrhonotus multicarinatus) were found in the stomach of still another. Woodbury (1931:75) recorded that a racer from Utah had a sagebrush scaly lizard (Sceloporus graciosus) in its stomach. Of the specimens examined in the University of California Museum of Vertebrate Zoology, no. 17256 from the Mad River, Trinity County, California, had eaten an alligator lizard (Gerrhonotus coeruleus), and no. 10120 from Yolla Bolly Mountain in the same county had eaten a bird (unidentified) and a Jerusalem cricket (Stenopelmatus sp.).

Several authors have published specific information regarding the food of C. c. flaviventris. Hurter (1911:171) caught a blue racer in the act of swallowing a copperhead (Agkistrodon contortrix). Taylor (1892:331) recorded finding garter snakes in several large racers. Pope and Dickinson (1928:53) recorded instances of blue racers feeding on racerunners (Cnemidophorus sexlineatus). Ortenburger (1928:181) examined 22 stomachs and recorded: 1 large garter snake (Thamnophis sirtalis), 1 vole (Microtus pennsylvanicus), 1 frog (Rana sp.), 31 crickets (Gryllus assimilis), 4 decticines, 2 acridids, grasshoppers (1 Hippiscus, 2 Melanoplus sp., 1 M. confusus, 1 M. differentialis, 1 Dissosteira carolina, 1 Sphargemon collare, 1 Trimerotropus sp., 1 Orphulella sp., 1 Chloealtis conspersa, 1 Chortophaga viridifasciata, 1 Omaseus sp., 1 Pedocetes sp.), and 2 caterpillars (1 noctuid, 1 sphingid). Gloyd (1928:123) recorded a hatchling glass lizard (Ophisaurus attenuatus) in the stomach of a juvenal racer. Force (1930:31) found a racer eating eggs from the nest of a cardinal (Richmondena cardinalis) and another racer eating eggs of a red-wing (Agelaius phoeniceus). Gloyd (1932:403) recorded an observation of a racer overpowering and swallowing a copperhead. Anderson (1942:210) recorded remains of crickets and grasshoppers in feces. Hudson (1942:55) recorded a racerunner (Cnemidophorus sexlineatus) in the stomach of a juvenile and recorded an earless lizard (Holbrookia maculata) 3 lizard eggs, and 14 grasshoppers (Melanoplus differentialis and others) in the stomach of another. Marr (1944:484) found a harvest mouse (Reithrodontomys montanus) in one. Breckenridge (1944:118) recorded stomach contents including a garter snake (Thamnophis sirtalis), a frog (Rana pipiens), 3 crickets and 2 moths. Mossimann and Rabb (1952:27) recorded that a racer disgorged several grasshoppers. Fouquette and Lindsay (1955:411) recorded that a blue racer had eaten a harvest mouse (Reithrodontomys sp.). Carpenter (1958:114) recorded that one blue racer had eaten a green snake (Opheodrys aestivus) and another had eaten a grasshopper and a camel cricket.

Even though the sets of data cited above are not entirely comparable, certain trends are evident. The black racers of the eastern states (especially C. c. constrictor of more northern regions) take a high proportion of vertebrates in their prey. Among these vertebrates snakes especially are well represented and the black snake would seem to be of some importance as an ophiphagous predator. The birds and mammals taken include some that are bulky (robin, cottontail, and even a weasel--the most formidable prey eaten). Presumably the rabbits that were eaten were young. In samples from the eastern United States insects made up small to insignificant parts of the food; they were lacking entirely or at least were not mentioned in the samples examined by McCauley and Wright and Bishop. In the blue racer of the central states, insects (mostly grasshoppers and crickets) are much more prominent in the food and vertebrates correspondingly less prominent. The vertebrates eaten are largely lizards, small snakes and mice. C. c. stejnegerianus is much like flaviventris in the trend of its feeding. C. c. mormon is less known than these subspecies in its feeding, but indications are that it takes a higher proportion of orthopteran insects and smaller proportions of mammals and snakes than do any of the other subspecies.

In my own field study a total of 1357 food records were accumulated, one of the largest samples known for any kind of snake. Most of these records were from the small area where my population study was carried on, and studies of other kinds of animals, including those that were the racer's prey, were simultaneously in progress. Because large collections of reference materials were available, it was possible to identify to species many of the prey items found, even though they were incomplete and highly fragmented because most of them were recovered from fecal material.

The prey is, of course, swallowed entire, and the recently swallowed items squeezed from the stomachs provide the best material for the study of food habits. However, relatively few racers had detectable food items in their stomachs; digestion is rapid and often the snake was in a trap for a day or more before it was found. Therefore the greater number of records were obtained from scats. The residue in scats consisted entirely of hard and indigestible parts such as the chitin of insects' exoskeletons and the hair, feathers, scales, teeth and occasional bone fragments of the vertebrate prey. The insects eaten could usually be counted individually by sorting parts, such as heads or hind legs. With mammals, birds and reptiles the hair, feathers, or scales did not permit counting of individuals--each occurrence was assumed to represent one individual but in some instances two or more may have been present. Amphibians, lacking indigestible dermal structures were in most instances not represented at all in the scats, since their tissues were more or less completely dissolved by the digestion of the snakes. Soft-bodied larvae of insects and other invertebrates conceivably could be likewise completely digested, but such occurrences must be rare, as most of the invertebrates known to be eaten have the mouth parts, at least, heavily chitinized.

Admittedly the factors discussed above would cause some bias in the percentage composition of the food determined from scats, but I believe that the amount of error introduced was slight, because, judging from the records of items from stomachs, amphibians are not eaten frequently, and even mammals are not eaten frequently enough so that there is much chance of a snake taking two or more individuals at the same meal, unless it is robbing a nest containing a litter of young.

The largest sample, based on 1008 food items, was obtained from 479 scats collected from the Reservation and Rockefeller Tract over the period 1949 through 1961. Items recorded were: 183 gryllid crickets (144 Gryllus assimilis, 36 Gryllus sp., 3 unspecified); 353 locustid grasshoppers (41 unspecified, 73 Arphia simplex, 67 Melanoplus femur-rubrum, 66 M. bivittatus, 39 M. differentialis, 17 Melanoplus sp., 15 Dissosteira carolina, 8 Chortophaga viridifasciata, 6 Syrbula admirabilis, 6 Sphargemon equale, 2 Melanoplus scudderi, 2 Schistocerca obscura, 1 S. americana); 94 camel crickets (Ceuthophilus sp.), 93 katydids (36 Neoconocephalus robustus, 15 Orchelimum vulgare, 15 O. nigripes, 6 Conocephalus sp., 4 Orchelimum sp., 2 Amblycorypha inasteca, 1 Neoconocephalus sp., 1 Daihinia brevipes); 7 cicadas (5 Tibicen sp., 1 T. pruinosa, 1 T. lyrica); 45 unidentified insects; 17 beetles (including 1 Phyllophaga, 1 Calosoma scrutator, and 2 other carabids); 2 noctuid moths (Mocis latipes) and 1 caterpillar; 2 homopterans, 1 bee, 1 ant, 1 spider; 69 voles (59 Microtus ochrogaster, 9 Microtus sp., 1 M. pinetorum); 31 white-footed mice (15 Peromyscus leucopus, 14 Peromyscus sp., 1 P. maniculatus); 36 miscellaneous small mammals (6 Cryptotis parva, 4 Sigmodon hispidus, 4 Reithrodontomys megalotis, 3 Blarina brevicauda, 2 each of Scalopus aquaticus, Sylvilagus floridanus, and 1 unspecified shrew); 50 snakes (16 Coluber constrictor, 15 Diadophis punctatus, 14 Thamnophis sirtalis, 4 Elaphe obsoleta, 1 Natrix sipedon); 7 lizards (5 Eumeces fasciatus, 1 E. obsoletus, 1 Cnemidophorus sexlineatus); 3 unspecified "reptiles"; 5 birds (none identified to genus); 3 bird eggs, 1 narrow-mouthed toad (Gastrophryne olivacea).

Over the same period that the sample of scats was collected, a much smaller food sample of 73 prey items was collected by squeezing recently eaten food from the racers' stomachs, or by finding the snakes actually swallowing their prey. These items from stomachs are listed separately because they include relatively more vertebrates than do the items from scats. A grasshopper or cricket eaten by a large racer might have passed undetected, while a relatively large item such as a vole or lizard would have produced a conspicuous bulge in the snake that ate it, and would have excited the curiosity of the investigator. A second difference is that the items from stomachs included several frogs, whereas amphibians were absent from the much larger sample from scats. A third difference is that the many insects found in stomachs were all orthopterans with the exceptions of three noctuid moths and the larva of a moth. Miscellaneous insects, such as beetles, bees and ants recorded from scats were not found in stomachs. Amphibians eaten are digested so completely that no recognizable parts of them are to be found in scats, but remains of the insects previously eaten by amphibians are to be seen in racers' scats. If not recognized as secondary items, such remains might lead to erroneous conclusions regarding the racer's food.

The items from stomachs were as follows: 21 grasshoppers (5 oedipines, 4 tryxalines, 5 Melanoplus bivittatus, 3 M. differentialis, 1 M. femur-rubrum and one each of Chortophaga viridifasciata, Dissosteira carolina, and Sphargemon equale); 8 crickets (Gryllus sp.), 3 katydids, 3 camel crickets (Ceuthophilus sp.), 3 noctuid moths, 1 larva of a moth; 10 voles (Microtus ochrogaster), 6 white-footed mice (5 Peromyscus leucopus and 1 P. maniculatus), 4 harvest mice (Reithrodontomys megalotis); 1 shrew (Cryptotis parva); 4 snakes (3 Thamnophis sirtalis, 1 Storeria dekayi); 4 lizards (2 Eumeces obsoletus, 1 Cnemidophorus sexlineatus, 1 Ophisaurus attenuatus); 4 frogs (Rana pipiens), 1 tree-frog (Hyla versicolor).

Records from the Harvey County, Kansas study area include a series of 69 food items from 55 stomachs (of living snakes) and 210 food items from 113 scats. There is a relatively high proportion of vertebrates, including some frogs, in the stomachs, and with no frogs but more miscellaneous insect material in the scats. But, for the sake of brevity, the two categories of items are combined in the following list: 55 grasshoppers (12 unspecified, 1 "locustid," 31 "oedipines," 7 "tryxalines," 5 "locustines," 2 Melanoplus bivittatus and one each of M. femur-rubrum, M. scudderi, M. differentialis, and Arphia simplex); 48 crickets (31 Gryllus assimilis, 17 unspecified); 14 katydids (11 Daihinia brevipes, one each of rhadiphorine, conocephaline and Neoconocephalus sp.); 9 noctuid moths and 1 moth larva; 26 miscellaneous insects (including 13 "beetles," 1 elaterid, 1 curculionid, 1 lygaeid bug, 1 ant, 1 wasp); 1 spider, 7 mice (5 Peromyscus maniculatus, 2 unspecified), 4 unidentified mammals, 1 vole (Microtus ochrogaster), 1 shrew (Cryptotis parva), 84 lizards (77 Cnemidophorus sexlineatus, 6 Sceloporus undulatus, 1 unspecified), 6 snakes (4 "natricines," 1 Thamnophis sp., 1 Pituophis melanoleucus), 1 "reptile," 1 "bird," 9 frogs (4 unspecified, 1 Rana catesbeiana, 4 Rana pipiens, 1 Rana sp., 1 Pseudacris triseriata).

Kinds of Prey

Throughout the range of the racer small mammals make up an important portion of the food, and the bulk of those eaten are voles (Microtus sp.) and white-footed mice (Peromyscus sp.). The voles being diurnal, and having habitat preferences similar to those of the racer, are especially subject to attack, but only large adult racers are capable of swallowing a full grown vole. Probably most of the voles eaten are immature. Of the white-footed mice, P. maniculatus especially prefers a grassland habitat, and is usually found in situations frequented by the racer. Being mainly nocturnal and crepuscular, it is usually in hiding at times when the racer is prowling, but may be flushed from its nest in a shallow burrow or beneath a sheltering object, and overtaken by the snake. Other mammals that are important in the food are harvest mice and other mice, shrews, and young cottontails. The latter are small enough to be eaten by racers only in the early stages of their life in the nest before weaning. Rats (Rattus, Sigmodon), moles, sciurids, and weasels are less frequent prey, ordinarily too large to be eaten by racers and taken chiefly as defenseless juveniles.

Predation on birds is relatively uncommon, and in most instances it involves the eggs or nestlings, or fledglings still slow and clumsy and incapable of sustained flight, or, occasionally, injured adults. Nests that are vulnerable are chiefly those of ground nesting species, or of kinds that nest near the ground in grass or thickets. Many of the birds recorded have not been identified to species, but those identified have included a variety of small passerines and also domestic chicks.

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