Worldwide the family Bombyliidae contains upwards to 6,000 species which are distributed on every continental land mass except the areas of the extreme north and south. Within the Nearctic region approximately 1,200 species are known. The majority of the species are found in the arid southwestern United States and in northern Mexico. It is estimated that more than 80 % of the bombyliid fauna of the Nearctic is found within this area.
The format for the present work will essentially follow the arrangement given in the Catalog of the Diptera of North America north of Mexico (Painter 8C Painter 1965), with the exception of the Systropodinae. Following the lead of European workers the members of the SystrOpodinae, Systmpus and Dolichomyia, have been accorded familial status and as such will be treated separately. As each subfamily is completed a complete bibliography will be inserted for that subfamily before going on to the next.
Because the Bombyliidae of the Nearctic are so poorly known we have elected to postpone remarks concerned with classification, phylogeny, biology and morphology until the study of all the genera and species has been completed. It is with this in mind that we hope to obtain a better insight into these areas which certainly are in need of study.
The following key separates the thirteen subfamilies of Bombyliidae currently recognized as occurring within the Nearctic region. For comparative purposes as well as completeness the family Systropodidae is also included in the key.