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) | |
| 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.
Stomachs of two adults of muticus from Lake Texoma, Oklahoma, were opened. The stomach of one (OU 27593) was full of naiads of the burrowing mayfly Hexagenia; that of the other female (OU 27594) contained exoskeletal remains of crawfish. The two specimens were drowned in gill nets between the hours of 11 a. m. and 7 p. m., on July 10, 1954; the intact condition of the mayfly naiads indicated recent feeding.
The species of American softshells are mainly carnivorous. The presence of vegetable matter (mentioned in previous paragraphs) in the digestive tracts of many specimens and True's statement (1893:152) that soft-shelled turtles include a variety of vegetable matter in their food indicates omnivorous habits. Duellman and Schwartz (1958:272) stated that ferox is omnivorous and Carr (1952:430) made a similar statement for spinifer. The diet seems to be determined by the food supply available, which may vary seasonally or with adverse conditions such as flooding; under normal environmental conditions, however, vegetable matter probably is ingested incidentally to other food. There is no indication of a preference in food habits according to species and subspecies. Most of the food seems to be obtained by active foraging that is triggered primarily by movement of the prey; the sense of smell is probably secondary.
Reproduction
Size of males at Sexual Maturity