Flies are well known as pollinators, but are understudied compared to other groups of pollinators, including bees and birds. The earliest references to their relationship with flowers date back to the 1870s, and include work by Charles Darwin. There has been no comprehensive analysis of the diversity of flies that visit flowers, or the flowers that they visit, but in 1990 I started collecting information from published papers, recording observations in an Access database. That database now includes observations from 935 publications and Web sites, with >33,000 entries from 89 countries, and Internet resources have made possible analyses that couldn’t have been done when I started data collection.

Individual studies have reported as many as 1,800 observations; the mean is 30 and median 4. 254 of 465 plant families (55%) have been reported to have flies as visitors to their flowers, with 9.3% of genera with animal-pollinated species included, and 0.7% of all the 298,700 species reported to be animal-pollinated. 67% of all fly families are reported to have species that visit flowers, including about 3.5% of all 152,000 species of flies. The five most common fly families visiting flowers are Syrphidae (by far the most), Tachinidae, Muscidae, Bombyliidae, and Anthomyiidae. The most commonly visited plant families are Asteraceae, Apiaceae, Rosaceae, Ranunculaceae, and Lamiaceae. A surprising diversity of flies can visit one species of plant; Daucus carota is visited by 219 species of flies from 137 genera and 33 families. A single species of fly (Episyrphus balteatus) is recorded visiting 836 species of flowers in 609 genera from 120 families. Of the records with the fly sex recorded, 60% are females, and 19% show both sexes visiting the flowers.  Japan is represented by 1,070 records from 49 publications, the sixth largest record from any country.

These results provide insights into the importance of flies as flower visitors, and the importance of floral resources for flies, and support the value of studying their interactions. Several important crop species are visited often by flies, highlighting the importance of conserving their populations.