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.