Mortality Factors and Adaptations for Survival 432 Defense and escape 432 Natural enemies 438 Disease 442 Parasites 442 Populations 445 Composition 445 Numbers 450 Summary 456 Literature Cited 461 Introduction Throughout much of the United States the racer is abundant and is one of the snakes best known to man. Its active diurnal habits and its preference for a habitat in meadows, pastures, and hayfields rather than in remote wilderness areas, result in frequent encounters with humans. The racer is a predator on many kinds of small animals, both vertebrates and invertebrates; it takes as food chiefly animals that are agricultural pests but also destroys some beneficial kinds. Yet, in general, the attitudes of rural people toward the racer are little influenced by these economic and ecologic considerations, but rather, are dominated by an unreasonable fear, despite the racer's inoffensive disposition, and inability to inflict any harm on humans. Although an extensive literature exists regarding the racer, no thorough study of the species' natural history has been made heretofore. Obviously such study is needed. Few species of vertebrates having comparable economic bearing have been similarly neglected. In 1948, undertaking a program of ecological research on the recently created University of Kansas Natural History Reservation, I included the racer among the many common species studied to gain insight into the functioning of the local ecosystem. Live-trapping of snakes on the area was begun in 1949, and these operations were greatly intensified in the years 1957 through 1962, with efforts concentrated on the study of the racer in the 1960, 1961 and 1962 seasons. Thus my study is based upon 14 consecutive years' records on the Reservation, the northeasternmost section in Douglas County, Kansas, six and one-half miles north northeast of the University of Kansas campus at Lawrence. After the acquisition in 1956 of the 160-acre Rockefeller Tract adjacent to the Reservation on the north in Jefferson County, field work was extended to this new area, which, because it was superior habitat, in the final years of the study produced more records than the Reservation. An important but relatively minor segment of the data originated from Harvey County Park, 13 miles west of Newton, Kansas, where lines of live-traps were maintained in 1959, 1960, 1961, 1962. Smaller collections of data were obtained from the Lalouette Ranch in the Flint Hills, three miles northeast of Florence, Marion County,