Clear fiber glass panels have been extensively used for constructing traps for stable flies,Stomoxys calcitrans(L.). Numbers of stable flies trapped on clear Alsynite fiber glass panels, covered with plastic film and adhesive, during 1-h periods at cattle feedlots, were related to concurrent measurements of air temperature, solar radiation, relative humidity, and wind speed. Temperature appeared to have greater effect on the trap collections than other weather variables, with maximum responses occurring between 25 and 31°C. Increasing radiation and increasing relative humidity both increased trap collections. Wind speed had no detectable effect. The differing effect of radiation on trap collections and on feeding activity of stable flies may account for previously noted differences between trap counts and counts of feeding flies for estimating population size.