Rocetelion humerale (Zetterstedt, 1850) (Diptera, Keroplatidae) rediscovered in Norway after more than 100 years, with description of the larva and its habitat.

Abstract

The large and conspicuous keroplatid species Rocetelion humerale (Zetterstedt, 1850) was previously documented with a single record from Norway only, a more than one hundred-year-old record of a male from Erfjord in Rogaland County, published in 1914, for which the voucher specimen has been searched for in vain in museum collections. In the summer of 2020, a new record of an adult male was photo-documented alive and then sampled from a barn in the village Førde in Sveio municipality, Vestland County. The following year, in October 2021, a population of larvae were located at a large, decaying log of beech (Fagus sylvatica) in the same area, a parsonage garden consisting of seminatural park landscape dominated by beech located just some 250 meters from the barn where the male was collected. The population of larvae living on this log was investigated also in 2022 with observations of active larvae in wintertime (early January), no findings in August but numerous spins and several larvae observed again in October. The living larvae were photo-documented and filmed. Five larvae were sampled, four of them successfully associated with the male through DNA barcoding. Both the adult male and the larvae are described and richly illustrated. Rocetelion humerale is redlisted as endangered (EN) in Norway and the new records are discussed in a wider context of records and the previous scarce knowledge of its biology abroad. The new data on its biology underscores the importance of leaving huge, windfallen logs of broadleaved trees to decay without cleaning up by removing them, and a practice to create fauna depots with large logs of dead wood in semi-park and park landscapes is suggested to help the species’ survival in lack of natural habitats with similar qualities.