A SURVEY OF SPIDERS (ARANEAE) WITH HOLARCTIC DISTRIBUTION

Of the 13,800 species distributed in the Holarctic Region only 395 are known both from Eurasia and North America. Of these only 105 species are distributed throughout the whole Holarctic (circum-Holarctic species). In addition, 28 species have an almost complete Holarctic distribution, occurring from Europe to northwestern North America (subcircum-Holarctic species). Species with a circum-Holarctic distribution were found in 13 families. The highest numbers of circum-Holarctic species were in the families Linyphiidae (37), Theridiidae (14), Araneidae (13) and Gnaphosidae (11). The percentage of the circum-Holarctic species among the Holarctic spiders is highest in Philodromidae (2.4%), Araneidae (2.2%), Theridiidae (2.0%) and Tetragnathidae (1.9%). These families encompass mainly herb-bush-tree dwellers. Somewhat unexpectedly it was found that most circum-Holarctic species occupy the boreo-nemoral zone (41%), or may even have a polyzonal range (23%). Twenty-nine species (28%) of the circum-Holarctic spiders have a northern distribution; most of them occurring both in arctic and boreal zones.