The history of Finnish Diptera catalogs starts with Evert J. Bonsdorff (1861, 1866), who reviewed a part of the brachyceran fauna known from the country at the time, totaling 657 species. Systematic maintenance and publishing of faunistic data began with the start of Wolter Hellén’s amazing series of summary papers covering new country records (and deletions) of all Insecta and running uninterrupted for six decades (Hellén 1922, 1926, 1931, 1936, 1941, 1946, 1952, 1956, 1961, 1966, 1971, 1976). Richard Frey, Lauri Tiensuu, and Ragnar Storå (1941) published the first complete list of Diptera recorded from Finland. It included 3824 species.

The era of Hellén culminated in a revised list of Finnish Diptera by Walter Hackman (1980a, 1980b, 1980c) in cooperation with Bernhard Lindeberg and Rauno Väisänen. The number of species had increased to 4852. Hans Silfverberg succeeded Hellén as the author of regular updates on additions and deletions to the Finnish insect fauna (Silfverberg 1981, 1986, 1991, 1996, 2007, 2012).

Nearly thirty-five years have passed since Hackman’s checklist. The number of Diptera species known from Finland has increased by more than two thousand species since 1980 (an increase of more than 40%). Several hundred erroneous records have been recognized during the same period. Many new names have been introduced and others found invalid, incorrectly used, or synonymized. The Diptera fauna of the whole Palaearctic Region has been catalogued (Soós and Papp 1984–1993) and many new local, regional, or global checklists have been published.

At this point, an updated checklist is urgently needed to provide a current reference to the Diptera fauna of Finland as a fresh starting point for further studies into the taxonomy, ecology, and other aspects of flies in Northern Europe.

There is no universally accepted definition for an entomological checklist. The word is often used for lists of species with more information than merely valid names, but without comprehensive details on nomenclature or distribution and incomplete literature references. This new checklist of Finnish Diptera falls into category 5 on the comprehensiveness scale of Thompson and Knutson (1987). It does include full names with authorships and some but not all synonyms. Some literature references are provided in an Suppl. material 2.

National insect checklists have traditionally included the species recorded at least once from the country. Exotic imports without locally reproducing populations are usually excluded, but vagrants are included. This is by no means the only possible approach: the latest Danish list (Petersen and Meier 2001) use a predictive approach: it lists not only the species actually recorded from the country, but also those that are likely to be present based on the fauna of neighboring countries. The latter method works best when the fauna of the surrounding areas is at least as well known as the study area.

This checklist covers the Diptera fauna of the Republic of Finland. Only species recorded at least once within the current (i.e. post-1944) borders are included.

Many species were originally reported from Finland on the basis of specimens collected from areas ceded to Russia in 1944. If no reliable records (preferably voucher specimens) from within the current borders of the country exist, species were excluded from the checklist. In some cases – e.g. the muscid Coenosia comita (Huckett, 1936) – it has been impossible to determine whether the purported Finnish collecting localities fall within the current borders of the country. These species are indicated with a question mark on the checklist and are usually accompanied by a comment in the Notes section of the relevant paper.

No fossil or subfossil records were considered during the preparation of the checklist. Nationally extinct species are included. In practice, the oldest collected Diptera specimens from Finland are from the early 19^th century, so all of the species in this checklist have been found in the country at least once during the last two hundred years.

Draft checklists for each family were created in the latter part of 2012 by combining data from the most recent checklist of the Finnish fauna of the family in question, the Palaearctic Catalog (Soós and Papp 1984–1993), Fauna Europaea (Beuk and Pape 2012), Silfverberg’s updates to Hackman’s checklist and references therein, other relevant scientific literature, and the Finnish Insect Record Database (Finnish Museum of Natural History 2013). From here onwards, the individual authors of each checklist paper were responsible for data validation.

For a great majority of families, the next step was examining the major Diptera collections in Finland (see the Acknowledgments). Fortunately, these collections have voucher specimens for most Diptera species reported from the country. If no recently identified specimens from the country could be found, the reliability of the record was judged by section authors based on details provided in the literature. For example, the record of Alliopsis longiceps (Ringdahl, 1935) from Finland was rejected. While Ringdahl correctly recorded this species from Finland in 1935, the type location (“Kuusamo bei Paanajärvi”) is now Russian territory, and no later observations have been published.

Exceptions to the procedure include Trichoceridae, Ceratopogonidae, Cecidomyiidae (subfamily Cecidomyiinae), and Phoridae (genus Megaselia Rondani, 1856), for which the checklists are largely based on a critical literature review. For more details on sources and validation, see the introductions and notes of individual checklist papers.

The new checklist of the Diptera of Finland is presented in three formats: a series of papers each covering one or more families, a comma separated values (CSV) file with the full taxon list, and a PDF (portable document format) file with literature references for species records. The latter two are included as electronic appendices to this paper.

All checklist papers follow the same general format. An introduction to the families covered is followed by a table or list of number of species recorded from the world, Europe, and Finland. An estimate of the faunistic level of knowledge is also given on a simple three-step scale (poor–average–good). This estimate is admittedly very subjective, being based on individual authors’ judgment. The following factors were considered: the number of species known from Finland in comparison with neighboring countries, taking into account known habitat preferences, etc., of absent species; the number of specialists who have worked with Finnish fauna; the number of publications on the Finnish fauna; and the quantity and quality of identified material collected from Finland.

The Checklist section of each paper starts with the systematic position of the family or families treated. As an example, the checklist of lauxanoid flies starts with:

suborder Brachycera Macquart, 1834

clade Eremoneura Lameere, 1906

clade Cyclorrhapha Brauer, 1863

infraorder Schizophora Becher, 1882

clade Muscaria Enderlein, 1936

parvorder Acalyptratae Macquart, 1835

superfamily Lauxanoidea Macquart, 1835

The family-level classification used follows mostly Marshall (2012), with exceptions noted in the Introductions of individual papers. The presentation order of subfamilies, tribes, genera, and subgenera can be either alphabetical or systematic depending on the author’s preference. Species are always listed alphabetically within a genus or subgenus.

Each species record starts with the name of the taxon, the author’s name, and the year of description. Doubtful records are indicated with a question mark (?) before the species name. The valid name may be followed by one or more additional names used for the same taxon. These names can be younger synonyms, preoccupied names, misidentifications, or common misuses in Finnish or international literature. As an example, the following entry lists three additional names used for Rhamphomyia trilineata.

Rhamphomyia trilineata Zetterstedt, 1859

= sulcatina Collin, 1926

= tibialis auct. nec Meigen, 1822

= propinqua misid.

R. sulcatina Collin is a younger synonym of R. trilineata. The name R. tibialis Meigen was erroneously used for this species by Frey (1956) and others; the genuine R. tibialis of Meigen has not been found in the Nordic countries. Frey et al. (1941) misidentified this species as R. propinqua de Meijere (in reality a junior synonym name for R. sulcata Meigen).

Table 1 lists abbreviations used in the checklist papers.

The checklist section is followed by a list of species not included on the checklist for various reasons. Excluded species comprise species recorded only from areas ceded to Russia before 1945, exotic species occasionally imported to Finland by man without locally reproducing populations, records based on misidentifications, etc. The Notes section presents authors’ comments on individual taxa.