Although the racer depends to a large extent on sight to find its prey, scent may play some part also, as indicated by the presence in the food of young mammals taken from nests, some probably found underground. Near Garnett, Kansas, on May 4, 1952, Richard B. Loomis found a racer attacking a collared lizard (Crotaphytus collaris) beneath a large flat rock. The lizard was retaliating by biting the snake's neck. The posterior part of the snake protruded into the open, and its thrashing had directed the attention of the observer to it. Whether the racer first found the lizard under the rock, or followed it there after flushing it in the open is unknown.
An encounter between a large blue racer and an adult Great Plains skink (Eumeces obsoletus) on August 30, 1948, was described as follows: "The skink, grasped by one flank, had twisted back and seized the skin of the snake's neck in a bulldog grip, and they lay interlocked, motionless except for their rapid panting, and occasional straining of the skink to bite harder or of the snake to shift its grip and work its jaws toward the skink's head. The racer broke the skink's grip, and began to swallow it head first. When only the hind legs and tail of the skink still protruded from the racer's mouth, I lunged forward in an attempt to catch both reptiles. With a sudden movement the snake disgorged the skink, which darted away into the grass and escaped" (Fitch, 1955:78).
Many authors have contributed to knowledge of the racer's food habits. In most instances the records have been few or casual, but several intensive studies have been made, notably by Surface (1906) in Pennsylvania, Ortenburger (1928) for the species as a whole, Uhler, Cottam and Clark (1939) in Virginia, Clark (1949) in Louisiana, Auffenberg (1949) in southern Texas, Hamilton and Pollack (1956) in Georgia, and Klimstra (1959) in southern Illinois. However, the findings of different authors are not strictly comparable; some have made general statements concerning the food habits but have mentioned specific items only when these were considered unusual. Certain authors have listed individual prey animals eaten; others have indicated the percentages (in bulk or in frequency) that the different kinds of prey comprised. Some writers have identified food animals only in broad categories such as "insect," "beetle" or "snake" while others have undertaken specific determinations for all the prey or for certain taxonomic groupings that were subjects of special interest.
For the eastern black racer (C. c. constrictor) the following food items have been recorded: 1 robin (Turdus migratorius, Storer, 1839:226); 1 copperhead (Agkistrodon contortrix, Verrill, 1869:158); 1 weasel (Mustela sp.—presumably the diminutive M. rixosa—Atkinson, 1901:148); 3 undetermined mammals, 1 rabbit, 1 undetermined mouse, 7 voles (2 Microtus sp., 4 M. pennsylvanicus, 1 Clethrionomys gapperi), 1 undetermined bird, 2 robin eggs, 2 garter snakes (Thamnophis sirtalis), 1 water snake (Natrix sipedon), 1 grass snake (Opheodrys vernalis), 1 green frog (Rana clamitans), 1 wood frog (R. sylvatica), 1 grasshopper (Melanoplus femur-rubrum) 2 camel crickets (Ceuthophilus sp.), 5 moths (cecropia, regal, imperial), 4 beetles, 1 currant worm, 1 ichneumonid wasp (Nematus ribesii), 1 currant worm (Surface, 1906:170); 1 ribbon snake (Thamnophis sauritus, Ditmars, 1907:282); 3 snakes (1 Liopeltis vernalis, 1 Storeria occipitomaculata, 1 undetermined), 6 white-footed mice (1 Peromyscus leucopus, 5 P. nuttalli), 1 vole (Microtus pennsylvanicus), 16 crickets (9 Gryllus pennsylvanicus, 4 G. assimilis, 2 Miogryllus verticalis, 1 Nemobius fasciatus), 2 grasshoppers (Dissosteira sp.), 1 lepidopteran, 3 elaterid beetles (Ortenburger, 1928:200). Richmond and Goin (1938:310) recorded finding the stomach of a black racer crammed with June beetles (Phyllophaga). Conant (1938:53) recorded a black racer from Ohio that had a smaller individual of its own species in its stomach. The smaller snake contained a caterpillar. Uhler, Cottam and Clark (1939:34) found food in 16 of 34 black racers from Virginia. Mammals, including a shrew (Blarina brevicauda), a mole, a flying squirrel (Glaucomys volans), a microtine, and a mouse (Peromyscus sp.) made up 26 per cent, 2 worm snakes (Carphophis amoenus), 2 ring-necked snakes (Diadophis punctatus), and 1 water snake (Natrix sipedon) made up 25.6 per cent, 5 birds including a warbler and a sparrow, made up 17.75 per cent; 2 frogs (Rana sp.) made up 9.38 per cent, 1 fence lizard (Sceloporus undulatus) made up 6.25 per cent, and insects, including cicadas (Tibicen sp.) and larval lepidopterans, made up 15.09 per cent. In Indiana, Minton (1944:457) examined 11 food-containing stomachs; there were rodents in six, snakes in five, a tree frog in one, and insects (cicadas, large grasshoppers) in four, and another black racer was found swallowing a small box turtle (Terrapene carolina). In Maryland, McCauley (1945:75) examined eight digestive tracts and recorded a shrew (Blarina brevicauda) in one, an unidentified mammal in one, 2 small cicadas in one, 2 small chickens in one, a fence lizard (Sceloporus undulatus) in one, and frogs and toads (including Hyla crucifer) in one; a ninth snake had eaten a half grown rat. In Connecticut, Finneran (1948:124) observed a large black racer eating a 21-inch garter snake (Thamnophis sirtalis). Duellman (1951:338) recorded a black racer in Greene County, Ohio, swallowing a large garter snake (Thamnophis sirtalis). In Kentucky, Barbour (1950:104) recorded remains of an unidentified snake in one stomach.
Many authors likewise have recorded food of the southern black racer (C. c. priapus). In Georgia, Wright and Bishop (1915:160) recorded finding 2 racerunners (Cnemidophorus sexlineatus), a skink (Lygosoma laterale), 4 green tree frogs (Hyla cinerea) and 1 pine woods tree frog (H. femoralis) in stomachs. They also stated that the toad (Bufo lentiginosus [= terrestris]) was the most important article of food. Burt and Hoyle (1934:205) wrote that a racer from Rogers County, Oklahoma, had eaten an adult male collared lizard (Crotaphytus collaris). In Florida, Carr (1950:80) found one of these black racers eating a leopard frog (Rana pipiens). Hamilton and Pollack (1956:523) examined digestive tracts of 62 and found food in 57, comprising the following percentages by volume: Lygosoma laterale, 34.2; Eumeces fasciatus and E. egregius, 11.3; Cnemidophorus sexlineatus, 8.8; Sceloporus undulatus, 3.5; undetermined lizard, 3.5; Opheodrys aestivus, 6.6; Diadophis punctatus, 3.1; Storeria dekayi, 1.6; Coluber constrictor, 1.8; Heterodon platyrhinos, 1.8; Masticophis flagellum, 1.8; Rana sp., 5.3; Hyla cinerea, 1.8; Hyla versicolor, 1.8; Peromyscus, 1.8; undetermined rodent, 1.8; lepidopterous larva, 1.7.
In southern Illinois in an intergrading population of racers intermediate between C. c. priapus and C. c. flaviventris, Cagle (1942:188) examined several stomachs and found 1 chipmunk (Tamias striatus), 2 voles (Microtus sp.), 2 mice (Peromyscus sp.), 2 green snakes (Opheodrys sp.), 1 water snake (Natrix sipedon) and grasshoppers. From this same population Klimstra (1959:212) examined 137 digestive tracts of which 115 contained food as follows: 194 locustids, 118 gryllids, 17 undetermined beetles, 13 carabids, 6 scarabaeids, 10 lepidopterans, 9 hemipterans, 1 hymenopteran, 2 homopterans, 1 dipteran, 17 undetermined insects, 73 Peromyscus sp., 19 Microtus ochrogaster, 9 M. pinetorum, 12 Sylvilagus floridanus, 3 Scalopus aquaticus, 3 Rattus norvegicus, 4 Mus musculus, 2 Tamias striatus, 2 Synaptomys cooperi, 16 Rana pipiens, 8 Acris crepitans, 2 Rana clamitans, 2 R. palustris, 1 R. catesbeiana, 4 Hyla crucifer, 3 Pseudacris nigrita, 4 Lampropeltis calligaster, 4 Sceloporus undulatus, 4 Chrysemys picta, 1 Heterodon platyrhinos, 1 unidentified reptile, 4 Sturnella magna, 1 Otocoris alpestris, 4 unidentified birds. Percentages by volume of the various categories in this sample were: insects, 39.1; mammals, 32.9; amphibians, 10.8; reptiles, 8.3; birds, 6.3; miscellaneous, 2.6.
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.).