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.
Fig. 13. Diagram showing percentage frequency of occurrence of various categories of prey in a sample of 1008 food items identified from scats and stomachs of blue racers from the Reservation and Rockefeller Tract. Insects, especially, orthopterans, made up the great majority of prey items taken.
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).
