_Methods of Obtaining Prey_
The racer hunts by stealth, but actively, obtaining its prey by keen
eyesight and swift movements. Wright and Bishop (1915:160) wrote that
because of its great speed it can catch anything that moves on the
ground. As a racer moves stealthily through dense vegetation, its
dull, uniform dorsal color blends well with the surface litter of dead
plant material. In prowling, the snake glides along rapidly and
alertly, in a jerky fashion, with frequent momentary pauses and
changes of direction. Because of its inconspicuousness, it is not
likely to be detected by the prey until it is close at hand. The snake
is ready to dash in pursuit of any small animal that flies, jumps or
runs to escape.
On August 27, 1955, my daughter observed a large racer hunting among
tall weeds at the edge of the pond on the Reservation. Several times
in the course of its movements, it flushed small frogs (_Rana
pipiens_) and each time the snake darted in unsuccessful pursuit of
the rapidly hopping frog. On several occasions I have been led to a
blue racer by the distressed croaking of a frog that the snake had
captured. In each instance, despite my cautious approach, the racer
saw me before I detected it, and then darted away, abandoning its
prey. On one occasion, while I was still a few yards from the racer,
and before the latter had detected me, the frog broke free and hopped
away rapidly through tall grass and weeds, and after several leaps,
hid, concealed by dense screening vegetation. The racer darted in
pursuit but could not find the frog. For several minutes the snake
persisted in an active search; with forebody elevated and head held
high, it would turn first in one direction and then in another, with
nervous, jerky movements, obviously keyed up to a high pitch of
excitement. Then it became aware of my presence, lowered its head, and
glided away rapidly, abandoning the search.
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).
_Composition of Food_
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.).
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.
[Illustration: 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_).
[Illustration: Fig. 14. Diagram showing estimated percentage by weight
of various categories of prey in a sample of 1351 items, including all
those represented in Fig. 13 and others from various parts of Kansas.
Since the vertebrate items are on the average much bulkier than the
insects eaten, vertebrates comprise most of the food, even though
insects are eaten in much larger numbers.]
[Illustration: Fig. 15. Diagram showing estimated percentages by
weight of various categories of prey in a sample of 69 food items
squeezed out of stomachs of the blue racers captured at Harvey
County Park. Most of the items were vertebrates, and lizards
(_Cnemidophorus_) were especially prominent in the food at this
locality. Samples of prey from scats (included in Figs. 13 and 14) and
from stomachs show somewhat different trends, and neither is entirely
representative of the actual feeding. Also, local differences in food
sources are important.]
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.