The subfamily Tachydromiinae (Diptera, Empididae) is a group of small flies, 0.7 to 5.5 mm in length, that is generally highly adapted for predaceous activity. An exact knowledge of the North European fauna is very important, not only because of its presumed origin in these regions but also because the first taxonomic works to include descriptions of new taxa were based solely on material from this region. The pioneers of Scandinavian and world entomology tended to overlook the tiny tachydromiines.
As such, revisional studies have been a primary task of the present author, and as a result of intensive sstudy over several years the individual taxa have been defined and delimited. Altogether 128 species of Tachydromiinae in 9 genera have been found in Denmark and Fennoscandia; a few further species may be expected to occur there but the number will certainly not increase very much. All the species included here are distinguished on the basis of the male genitalia in addition to the external characters, and the more important diagnostic features including the male genitalia are illustrated, most of them for the first time. Each species is very briefly described or differentiated from the most closely related species, and, so far as the limited scope of the fauna allows, brief records on the distribution in Fennoscandia, the entire range of distribution, the flight-period and notes on the biology are given. Species which may also be are often included in the key where they appear without numbering.