Stable flies are among the most important arthropod pests of livestock throughout much of the United States and cause production losses approaching 1 billion dollars per year. Traditionally a pest of confined livestock, in recent years stable fly has emerged as a primary pest of pastured animals as well. The sources of stable flies, especially in pastures, have not been well documented. The purpose of this study was to document and characterize stable fly larval habitats relative to seasonal population levels. Potential stable fly larval habitats were sampled to verify the presence of stable flies. Emergence traps were used to monitor seasonal production. Adult populations were monitored with Alsynite sticky traps. Two peaks of adult stable fly populations were observed, one in early summer and the other in late summer. Large-round-bale feeding sites were the primary source of early season stable flies. The sources of late season flies remain unclear.