Does citizen science contribute to the study of lesser-known species groups? The case of volunteers and dolichopodid flies in Flanders (Belgium) (Diptera: Dolichopodidae)

Since 1981, Dolichopodidae have been rather intensively surveyed in Belgium and Flanders, the northern part of Belgium, in particular, producing the first Red List of Dolichopodidae of Flanders. Subsequently, over 633,000 specimens of 271 species have been collected and identified. The sampling sites cover 41% of the UTM 5 km grid cells in Flanders, making it one of the best studied regions for Dolichopodidae in the world. At a resolution of 1 km, however, they account for only 3.7% of the Flemish territory, which rendered an updated version of the Red List non-IUCN compliant. During nearly three decades, most of the dolichopodid data collection has been undertaken by professionals, but times are changing. Thanks to the data portal “waarnemingen.be” and the mobile application “ObsMap” since 2008 citizens can easily upload observations and images of species and add an identification. These identifications are subsequently validated by taxonomic specialists. A total of 1,005 observations in the data portal, collected by 185 citizen scientists since 2008 and covering 193 UTM 5 km grid cells (30% of all 5 km grid cells in Flanders) were analysed. About 43% of the identifications proved correct and a species name could finally be assigned to three-quarters of the observations. Eighty-two of the 271 species were observed by volunteers, also including six very to extremely rare species. In general, however, proportionally more common species were better represented than rarer species. The role of citizen science in dolichopodid research in Flanders is further elaborated upon.