The rediscovery of Orthoceratium lacustre (Scopoli, 1763) (Diptera: Dolichopodidae) in Belgium, with data on its ecology and distribution in the Palaearctic region

Upon recent rediscovery of the dolichopodid Orthoceratium lacustre (Diptera: Dolichopodidae) in Flanders (northern Belgium) three sites with potential habitat of the species in Flanders were visited in September 2016. The survey revealed the presence of a population of the species at each site. In order to explain its apparent absence in Flanders for nearly the past 40 years, information on the distribution, ecology, phenology and conservation status of the species was gathered from the literature and available data sets and databases. O. lacustre has a western Palaearctic distribution and occurs in northwestern Europe, the Mediterranean basin and the Middle-East. It clearly prefers coastal salt marshes and brackish marshes in the first region, but also occurs near open water in forests at higher altitudes in the two latter regions. Whereas it reaches its activity peak in September in northwestern Europe, its main activity is situated at least two months earlier in the southern part of its distribution range. It is considered very rare in both Flanders and the Netherlands, nationally scarce in Great Britain, and currently extinct in Germany. A very strict habitat affinity, unusual phenology and/or effects of collecting methods seem responsible for its previous Red list status as ‘extinct in Flanders’.