Despite the economic importance of the muscoid flies as a group, very few quantitative data are available on the effect of temperature on the duration of the incubation period. Wardle ( 11 ) presented valuable data on the incubation period of eggs of Lucilia sericata Meig. at a series of constant temperatures. Notes on the incubation period of Stomoxys calcitrans L. by Melvin ( 5 ) and of Haematobia irritans L. by Melvin and Beck ( 6 ) are available.