"flipping" the loose sand or silt over the back, whereas Conant
(1951:159) described the process as a rapid lateral movement of the
body. My observations of captives agree essentially with Conant's
observations. The initial movement, directed at a slight angle, is
principally with the forelegs although complemented by lateral movements
of the body. When the turtle is approximately half buried, it makes
rapid lateral movements of the body, which completely bury the turtle
and orient its body in a horizontal position.
_Behavior and Adaptations_
Some characteristics of softshells that are often mentioned in the
literature are: extreme shyness or wariness, ferociousness as captives,
dazzling speed and agility on land and in water, and great dependence on
aquatic environment. Certainly they are wary; and this wariness may
account, in part, for the scarcity of observations of basking, and
statements attesting to their great speed on land. To my mind, their
reported ferociousness and savage disposition as captives is overrated;
of the many softshells that I have collected, only a few attempted to
bite. The extensibility of their long neck does warrant more careful
handling than needs to be employed with other species. Holbrook (_in_
Hay, 1892:145) even wrote that they "will sometime leap up and give a
loud hiss," and Newman (1906:130) wrote that "they hiss violently and
thrust out the head." Wright and Funkhouser (1915:120) reported a
captive _ferox_ that "could jump forward practically its own length." I
have been bitten by individuals of _Kinosternon_, _Sternothaerus_,
_Pseudemys_ and _Graptemys_, and cannot support the contention that
softshells are more prone to bite than those species, a view shared by
LeConte (_in_ DeKay, 1842:7); many softshells on initial capture will
tend to withdraw the head completely for a short time. Newman (_loc.
cit._) also wrote that recently captured specimens exude a thick,
yellow, semi-fluid resembling yolk of an egg from the inguinal glands;
the substance, however, is odorless but "undoubtedly homologous with the
emission of the inguinal glands of the musk and snapping tortoises."
Perhaps there is a difference in aggressiveness associated with
geographic location, the age of the turtle or individual temperament.
Smith (1956:159), referring to _muticus_, wrote that they are the best
swimmers of all fresh-water turtles, and perhaps of any turtles.
Corresponding statements of other authors attesting to their speed and
agility (including _spinifer_ and _ferox_) in water and on land are
based principally on the published comments of Muller (1921:181), who
observed that females disturbed while laying eggs "about fifty feet from
water ... covered the distance faster than a man can run." Cahn
(1937:180) also stated that _muticus_ on a "level, unobstructed sand
beach ... can outrun a man," and (_op. cit._:181) can "capture fish with
ease"; Cahn supported the latter statement by relating his observation
of a _muticus_ that captured a small brook trout in a large tank. Smith
(_op. cit._:162) wrote that _spinifer_ is "said to overtake bass."
Doubtless they are good swimmers and they do scurry rapidly on land.
Published statements relating to the strictly aquatic existence of
softshells especially _muticus_, are based on recognition of "its
drastic adaptations to aquatic existence" (Carr, 1952:428); these
adaptations presumably include pharyngeal respiration and the marked
depression of body form. Pharyngeal respiration was demonstrated for
_muticus_ and _spinifer_ (Gage, 1884; Gage and Gage, 1886), and was
considered the principal type of aquatic respiration (some dermal and
some cloacal) in _Trionyx spinifer asper_ by Dunson (1960). Cloacal
bursae (anal respiration) are lacking in trionychids (Smith and James,
1955:88). Accessory pharyngeal respiration is meaningful in light of the
information furnished by Agassiz (1857:282-83), who found that _Trionyx_
has a smaller lung capacity (weight of body in ounces/capacity of lungs
in cubic inches = 16.9) than do some other genera (_Pseudemys_, 2.8;
_Testudo_, 2.7; _Terrapene_, 1.1); corresponding values for more aquatic
species were _Chelydra_, 9.3 and _Kinosternon_, 16.0. Cahn (1937:181),
however, wrote that he has demonstrated pharyngeal respiration in
individuals of _Pseudemys_, _Chrysemys_ and _Sternothaerus_, and Allen
and Neill (1950:13) suggested that it occurs in _Macroclemys_. More
conclusive data are required to detect a positive correlation between
small lung capacity, pharyngeal respiration, and degree of restriction
to an aquatic habitat.
The depressed, soft-margined carapace of softshells has been mentioned
as an adaptation to facilitate burrowing in soft sand or mud, and more
suited for concealment than for speed in aquatic locomotion (Carr,
1952:429; Smith, 1956:162). Nielsen (1951:264-65), commented that in
various lotic invertebrates, dorsoventral flattening of the body was no
commoner than in lentic invertebrates; he wrote that a dorsoventral
flattening is a disadvantage to an animal in a strong current and is an
adaptation "probably ... not to withstand the current directly, but to
avoid it by seeking shelter in narrow crevices." Probably another aid to
concealment, mentioned by Williams and McDowell (1952:272), is the
plastral hinge.
Concealment of softshells is not enhanced by growths of algae on the
carapace. Proctor (1958:637-38) reported that the common, epizoöphytic
alga of chelonians, _Basicladia_, has never been reported from
_Trionyx_; the same author recorded a large amount of filamentous algae,
principally _Stigeoclonium_, but the algae could be easily wiped from
the turtle, and Vinyard (1955:64) recorded an alga, _Dermatophyton
radians_, attached to the skin of the legs of _Trionyx_. I noted a small
patch of greenish scum growing near the insertion of the neck on a
softshell (_spinifer_ from Lake Texoma); cursory examination by Dr. R.
H. Thompson, disclosed one of the colonial ciliate protozoans
(resembling _Opercularia_) with enmeshed green or blue-green algae.
Evermann and Clark (1920:592) mention a _spinifer_ from Lake
Maxinkuckee, Indiana, having a growth of _Opercularia_, covering the
plastron.
_Movement_
The reported proclivity of softshells for a strictly aquatic existence
has been over-emphasized; they are no more confined to aquatic habitats
than some chelydrids (including kinosternids). In fact, there is a
general parallel in habits between members of the two families, namely,
a tendency toward a bottom-dwelling existence, and a burrowing habit.
The alligator snapping turtle (_Macroclemys_) is probably the most
aquatic fresh-water turtle in the United States. The common snapping
turtle and some kinosternids are known to migrate overland. Kinosternids
and trionychids bask frequently, and trionychids have been observed
moving overland. Cox (1894:50) reported a _spinifer_ attempting to climb
a narrowly-stepped, 12-foot dam on Mud Creek at Ravenna, Nebraska; the
turtle failed after repeated struggles, once reaching a height four
inches shy of the brim before tumbling back into the water. Duellman and
Schwartz (1958:271) commented that adults of _ferox_ are often seen on
roads bordering canals, and informants have told me verbally of similar
observations. Conant (1930:61) reported an individual of _ferox_ that
was "... walking across the main street in Venice [Sarasota County,
Florida]." Softshells will travel overland in search for suitable
nesting sites; Newman (1906:130) wrote that _spinifer_ will climb "steep
railway embankments with considerable ease, in order to reach a sand pit
some fifty yards from the water."
From an analysis of species-composition of large reservoirs and lakes
and their adjacent smaller ponds in southern Illinois, Cagle (1942:162)
concluded that softshells "travel overland far less often than do ..."
other species, but that they are "probably the first to move as the
water level falls." On the basis of further observations in the same
region, Cagle (1944:15) wrote that softshells rarely move overland, and
once trapped in a pool of water, they bury themselves and remain there.
He related instances of several individuals having been dug from dried
mud where the last remnants of a water pool had evaporated and he
concluded that the home range is probably confined to one body of water.
That fluctuations in water level affect the movement of softshells is
suggested by Mr. William E. Brode's comment that a commercial fisherman
trapped numerous softshells in the Pearl River, south of Monticello,
Mississippi, in unbaited hoop-nets in late May and June when the water
level was receding after heavy rains.
The meager data available concerning the aquatic movements of softshells
indicate that individuals wander but little. Breckenridge (1955:6,
table 1) found that among 30 recaptured turtles that had been marked,
the greatest distance traveled was 600 yards over a two-year interval;
after a three-month interval one originally captured 30 miles distant,
moved only 200 yards. The statement of a professional turtle trapper
mentioned by Breckenridge (_loc. cit._) and data previously presented
(see page 436), to the effect that over-trapping results in increasingly
diminished returns, tends to support the idea that there is little
aquatic movement in soft-shelled turtles.
Breckenridge (_loc. cit._) mentioned methods of marking softshells and
found that notching the edge of the carapace with a leather punch was
satisfactory; the notches healed but were discernible as shallow
sinuses. The same author mentioned a tattooing device (mentioned also by
Cagle, 1939:171), but no turtles so marked were ever recognized as
recovered. Tagging with a radioactive isotope and detection with
suitable instruments should prove applicable to turtles (see Karlstrom,
1957).
_Nocturnal Habits_
Anderson (1958:212) wrote that hatchlings (_muticus_) leave nests within
the first three hours after sunset, and are active on the surface of the
sand at night. Muller (1921:183) reported hatchlings (_muticus_) leaving
nests at night or early in the morning. Lagler (1954) stated that
_spinifer_ is nocturnal. To my knowledge there are no other published
statements concerning nocturnal activity of soft-shelled turtles. I have
noted them at night on only four different occasions. In two instances
(Clear Fork Brazos River, Texas, and Lake Concordia, Louisiana), the
turtles were resting immediately below the surface of the water on
submerged branches, as one would expect _Pseudemys_ and _Graptemys_ to
do. Another individual was seen swimming near the surface (Ocmulgee
River, 1-1/2 mi. S Jacksonville, Georgia); this observation possibly
represents nocturnal activity, or inquisitiveness owing to the
disturbances caused by the motor of the boat and/or our head lights. A
final observation tends to support the view of nocturnal habits. My
field notes record at least four softshells collected by hand, and a few
other seen in a shallow (approximately four feet deep), quiet, clear
water side channel of the White River (Cotter, Arkansas); the turtles
were seen resting and slowly moving on the bottom or swimming.
_Seasonal Occurrence_
The length of the season of activity increases with decrease in
latitude. Aquatic species in general have longer periods of activity
than terrestrial species at the same northern temperate latitudes. The
southernmost populations of all species of softshells may be active
throughout the year, assuming temperature to be the limiting factor.
There are few published statements relative to the length of the annual
period of activity; all records refer to _spinifer_. In Lake
Maxinkuckee, northern Indiana, Newman (1906:128) wrote that individuals
were first seen in early April on the lake shore in a weak condition
with neck and legs extended, and were easily captured. Lesueur
(1827:262) wrote that _spinifer_ in Indiana appears toward the end of
April. Observations of Evermann and Clark (1920:592) in Lake
Maxinkuckee, and Butler (1894:224) in east central Indiana concurred in
finding that of all kinds of turtles there, softshells appeared last in
spring and disappeared first in fall. Evermann and Clark found small
softshells, benumbed or dead, along the shore as early as March 18 and
also late in fall. The earliest observation for large softshells was
April 29, and the latest was September 7; Butler found that these
turtles rarely appear before April 15 and sometimes not until May 1.
Cahn (1937:191) stated that softshells in Illinois hibernate toward the
end of October and emerge in May or the latter part of April; the same
author mentioned that in southern Illinois the species might remain
sluggishly active all winter. In Ohio, Conant (1951:160) wrote that
individuals were collected every month from March to October, and one
was even taken in December, 1929, in northwestern Ohio. Wright (1919:8)
mentioned observing softshells on April 20 and September 20 (presumably
these were the earliest and latest observations of them) in Monroe and
Wayne counties, New York. Blatchley (1891:34) listed dates of early and
late activity as March 19 and December 11 for Vigo County, Indiana.
Webster (1936:22) recorded the earliest and latest dates of collection
of _spinifer_ in central Oklahoma as June 10 and November 8.
Moore and Rigney (1942:80) found an individual of _muticus_ under six
inches of ice in water about one foot deep on January 31, 1940 (Cimarron
River, Payne County, Oklahoma).
The published information suggests that the length of the normal annual
period of activity of _spinifer_ in latitudes of about 40° and 43° is
approximately five months, from April into September, depending upon the
weather. There are numerous published statements to the effect that the
period of hibernation is passed under a shallow covering of mud in deep
water. Evermann and Clark (_op. cit._: 593) found a softshell
(presumably in a quiescent state) on September 6 that was "buried up to
its eyes in mud at the edge of Lost Lake." Softshells possibly hibernate
in shallow water or in soft mud flats. Conant (_loc. cit._) found that
captives would not hibernate in a pond in a zoo having a bottom of
leaves.
Food Habits
Previous authors, most of whom allude to published statements preceding
their own, characterize soft-shelled turtles as carnivorous and mention
such food items as crawfish, insects, worms, snails, clams, frogs,
tadpoles, fish, and occasional vegetable matter. Stockwell (1878:403)
wrote that the relative lengths of portions of the digestive tract
indicate "a purely carnivorous diet."
In an examination of the contents of 11 stomachs of _spinifer_ from
Michigan, Lagler (1943:304) found that crawfish (47%) and insects
(52%), principally burrowing mayfly naiads (_Hexagenia_), and
dragonfly naiads, comprised the bulk of the diet with cryptogams,
vegetable débris, snails and fish remains present in small amounts.
Breckenridge (1944:186) wrote that 18 specimens of _spinifer_ in
Minnesota contained 44 per cent crawfish, 29 per cent aquatic insects,
8 per cent fish, and 19 per cent unidentified material. Surface
(1908:123) found crawfish in the only two stomachs of specimens he
examined from Pennsylvania. Penn (1950) summarized the results of
those authors, and estimated that crawfishes comprised 58 per cent
(46% by volume) of the diet of softshells. In Indiana, three stomachs
examined by Newman (1906:131) in late June contained: 1) nine
crawfish, 2) four crawfish, 22 dragonfly naiads, 3) nine dragonfly
naiads, few plant buds. Neill (1951a:765) found crawfishes in the
stomachs of five _spinifer_ from the Savannah River, Georgia. Evermann
and Clark (1920:595) wrote that _spinifer_ in Lake Maxinkuckee feeds
principally on crawfishes. Shockley (1949:257) mentioned bottom
organisms and small fishes as food. Clark and Southall (1920:16)
stated that "Its principal food, to judge from a few specimens
examined, consists of crayfishes."
Cahn (1937:183) wrote that the food of _muticus_ in Illinois consists
principally of crawfish, fish, frogs, tadpoles, larger insect larvae
and nymphs, and aquatic mollusks. The kinds of fish eaten were
_Notropis heterolepis_, _N. spilopterus_, _N. hudsonius_, _Lepomis
machrochirus_, _Morone chrysops_, _Perca flavescens_, _Catostomus
commersonnii_, and _Hypentelium nigricans_; Cahn (_loc. cit._) also
stated that the mollusks eaten by _muticus_ are both gastropods and
small, thin-shelled bivalves. In regard to the feeding habits of
_spinifer_ in Illinois, Cahn (_op. cit._:193) listed the following
items in decreasing order of abundance as revealed by examinations of
stomachs: crawfish, minnows, fry of larger fish, frogs, tadpoles,
earthworms, insects (often beetles), and mollusca (_Pisidium_,
_Viviparus_, planorbids). The kinds of fish mentioned were: _Notropis
heterodon_, _N. heterolepis_, _N. hudsonius_, _Catostomus
commersonnii_, _Lepomis humilis_, _L. macrochirus_, _Semotilus
atromaculatus_, _Notemigonus crysoleucas_, _Umbra limi_, and
_Micropterus salmoides_. Cahn (_loc. cit._) also found the remains of
a six-inch brook trout (_Salvelinus_) in the stomach of a 13-inch
_spinifer_ from Wisconsin.
Agassiz (1857:399) found larvae of neuropterous insects in the stomach
of one specimen of _muticus_, and fragments of _Anodonta_ and
_Paludina_ (= _Campeloma_) in the stomach of one _ferox_. The expanded
crushing surfaces of the jaws in some large individuals of _ferox_ may
be an adaptation to mollusc-feeding (Schmidt and Inger, 1957:36).
Surface (1908:123) found _spinifer_ to have fragments of beetles in
one of two specimens examined, and large quantities of corn in another
from Ohio. Webb and Legler (1960:27) reported 23 chrysomelid beetle
larvae (_Donacia_) in one specimen of _T. ater_. Evermann and Clark
(1920:595) reported several _spinifer_ taken on hooks baited with
grasshoppers in water 14 feet deep in Lake Maxinkuckee, Indiana. Hay
(1892:144) wrote of _muticus_ that "If there are potatoes growing near
the water the turtles find their way to them and devour the stems, of
which they are very fond." Wright and Funkhouser (1915:123) stated
that young _ferox_ in the Okefinokee Swamp feed on fish and frogs, and
according to the natives, larger specimens take waterfowl, a statement
that Smith (1956:159) was probably reiterating when he mentioned that
the diet included "perhaps young birds." Parker (1939:88) wrote that
of two _spinifer_ from Reelfoot Lake, Tennessee, one contained
coleopteran remains, and the other an aquatic beetle and two large
tipulid larvae. Wied-Neuwied (1865:54) wrote that Lesueur found worms,
snails, remains of _Paludina_ (= _Campeloma_), fruits and even hard
nuts in stomachs of _muticus_.
Holbrook (_in_ Hay, 1892:145) mentioned that _spinifer_ feeds on fish
and such reptiles as it can secure. There are no published statements
known to me that report reptiles in the diet of American softshells.
Carr (1952:425) erroneously cited Strecker (1927:9) and attributed "a
young lined snake" to the diet of _T. s. emoryi_; Strecker, however,
referred to _Kinosternon flavescens_. In conjunction with raising
softshells on turtle farms, Mitsukuri (1905:261) mentioned that first
and second year-old turtles (_Trionyx sinensis_) must be transferred
to separate ponds or they will be eaten by adults; perhaps
corresponding cannibalistic tendencies exist in confined, natural
habitats in American softshells.
Captives eat essentially the same things that free-living individuals
do, plus scraps of meat (Strecker, 1927:9; Gloyd, 1928:135; Pope,
1949; Conant, 1951:156, 160). Lagler (1943:303) mentioned a young
_spinifer_ that fed on water fleas (_Daphnia_) and canned fish. Conant
(_op. cit._:160) wrote that no captive was observed to take vegetable
matter.
Food, mostly in intestines, of two adult females of _T. s. emoryi_
collected on June 12-14, 1959, from the Río Grande at Lajitas,
Brewster County, Texas, was examined. One female, KU 51961, contained
little food and mostly plant fragments; because the stomach or
intestine was not full of plant fragments, this food probably was
ingested incidentally to the few insects present. Another female, KU
51955, contained insects, which were identified by Dr. George W.
Byers, Department of Entomology, University of Kansas, as follows: 1)
Coleoptera, Dryopidae, genus _Helichus_, most numerous, 350 to 400
individuals; 2) Coleoptera, Scarabaeidae, genus _Phyllophaga_, one
individual; 3) Odonata, Coenagrionidae, fragments, probably one
individual; 4) Hymenoptera, Sphecidae, subfamily Bembicinae, one
individual; 5) Ephemeroptera; fragments of naiad; and 6) a few plant
seeds, pieces of slender roots, weed stems and a couple of fragments
of tree bark. The scarab and wasp probably fell into the water and
were eaten.
TABLE 6. Kinds of Insects Found in Stomachs and Intestines of 11
Specimens of Trionyx m. muticus (Eight Adult Males and Three
Immature Females, 9.0 to 12.5 cm. in Plastral Length) From Douglas
County, Kansas. Frequency of Occurrence (Approximate Number of
Individual Insects/Number of Stomachs in Which Found) Is Given for
Each Item Listed. Fragments of Insects Represent Adults Unless
Otherwise Noted.
==========================================================+===========
FOOD ITEM | Frequency
----------------------------------------------------------+-----------
Orthoptera |
Locustidae | 1
|
Ephemeroptera |
Unknown (naiad) | 1
|
Odonata |
Anisoptera (naiad) | 3/3
Zygoptera (naiad) | 4/2
|
Plecoptera |
Unknown (naiad) | 2/1
|
Homoptera |
Cicadellidae | 20/7
|
Hemiptera |
Lygaeidae | 1
|
Neuroptera |
Corydalidae (_Corydalis_ larva) | 1
|
Trichoptera |
Hydropsychidae? (incl. 18 larvae and 4 pupae) | 23/9
Unknown (incl. 1 larva) | 4/4
|
Lepidoptera |
Noctuidae? (larvae) | 2/1
Pyralidoidea (larva) | 1
Unknown | 1
|
Coleoptera |
Carabidae (incl. 1 larva) | 3/3
Cerambycidae? | 1
Chrysomelidae | 1
Cicindelidae (larva) | 1
Elateridae (larva) | 1
Hydrophilidae? (larvae) | 4/2
Scarabaeidae (incl. _Phyllophaga_) | 9/6
|
Diptera |
Anthomyiidae | 1
Asilidae | 1
Bibionidae (_Bibio_) | 5/2
Calliphoridae (puparium) | 1
Empididae | 1
Mycetophilidae | 1
Tipulidae (incl. _Tipula bicornis_ and _T. triplex_?) | 9/4
Unknown (5 muscoid, 3 acalyptrate, and 1 cyclorrhaphous |
types) | 9/4
|
Hymenoptera |
Apoidea | 1
Formicidae (incl. _Camponotus_) | 11/4
Ichneumonidae (one questionable) | 4/3
Tenthredinidae | 1
Unknown (small wasps) | 3/2
----------------------------------------------------------+-----------
Food from the digestive tracts of 11 specimens of _T. m. muticus_ from
the Kansas River at Lawrence, Douglas County, Kansas, were examined
(Table 6). The turtles (KU 55296-306, eight adult males and three
immature females, ranging in plastral length from 9.0 to 12.5 cm.)
were collected in June, 1958, by Mr. Robert R. Patterson. All turtles
were caught on hook and line in a period of about four or five hours
at dusk. Patterson frequently fished below the bridge at Lawrence and
observed that heads of softshells were often seen there about dusk and
that the turtles seemed to prefer a rather shallow, quiet-water area
of swirls and eddies for feeding. The stomachs, and to a lesser
degree, the intestines, were nearly full. Some turtles contained plant
fragments, principally elm seeds. The kinds of food in this sample
were also identified by Dr. Byers and were mostly insects, the most
frequent item being trichopterans; many of the insects eaten
undoubtedly fell into the water. The remains of spiders were found in
four stomachs and crawfish fragments in five.