Stable flies, Stomoxys calcitrans, have long been recognized as important pests of confined cattle, inflicting a painful bite, to which cattle respond by bunching together, thereby increasing heat stress and reducing feed intake. Ranchers and veterinarians, as well as livestock entomologists, university scientists, and animal health companies concur that stable flies have, in recent years, also emerged as a serious problem for grazing cattle in pastures and rangelands of North America. The extent of movement on regional scales and corresponding breeding structure of populations of these flies in North America are unclear. In a 2-year study, seasonal abundance of stable flies was studied in southeastern Nebraska. Stable flies were active from April to November in both years, and were captured using Alsynite sticky traps. Total adult populations followed the typical bi-modal pattern. A tri-model pattern was observed in the second year due to an unusually high rainfall event in early August. Total numbers of captured flies per week, female/male sex ratio, recency of blood meal, and physiological age-grades of females were recorded and analyzed. Males consistently outnumbered females in a 2 to 1 ratio, and there was a negative relationship between physiological age of females and total adult population profile.