Arachnologische Mitteilungen 56

Ten years after the invasion in Denmark (Opiliones) 3 1-6 specimen (mean 2.4) being found during the one-hour searches. It was absent from central and northwestern Jutland, most of Zealand, as well as Lolland-Falster and Bornholm. In 2017, D. ramosus had arrived to all parts of Denmark (Fig. 1B). In Jutland the species was nearly ubiquitous and was missed in only a very few survey visits (4 of 42 towns), in- dicating a more or less “continuous”distribution. On southern Funen, most of Zealand and Lolland-Falster, the species was present as indicated by reports to the database, but in any case it was missing in 15 out of 22 of the towns visited during the survey. The relative frequencies in Jutland and the islands are significantly different (Yates’ χ 2 = 10.05, df = 1, P = 0.0015). The number of individuals per visit in Jutland was 1-10 (mean 3.6), while on the islands it was 1-2 (mean 1.6) (excluding locations without the species). The first record from the iso- lated island of Bornholm, situated in the Baltic Sea between Poland and Sweden, is from 2017. The bee line distance between sites of first records in the Netherland (Ede) and Denmark (Årslev) is 482 km.This was accomplished by D. ramosus in 14 years, giving a displacement rate of 34.4 km/year. Records from Copenhagen 2009 and Skagen (northern tip of Jutland) in 2010 give displacement rates of 37.9 and 41.5 km/year, respectively. Similar calculati- ons from the site of the first German record (Schmidt 2004) produce values of 119.5, 97.7 and 104 km/year, respectively. As it is unknown whether the immigrants to Denmark came from Germany or the Netherlands, 35-40 km per year may be considered the cautious estimate. In Sweden, however, D. ramosus was recorded from Uppsala only 5 years after the first Swedish record (Artportalen 2018) giving a rate of expansion of 103 km per year. The finding of an established population at Poznań, Poland, 440 km east of the nearest known Ger- man locality (Rozwałka & Rutkowski 2016) also indicates the possibility of fast expansion by very long jumps. Odiellus spinosus (Fig. 2) has spread much less actively than D. ramosus .The number of localities and the total distribution area is smaller. It is widely scattered within its area which in 2017 included eastern Jutland and the islands (except Born- holm) with a relatively high concentration on the islands.The distributional pattern (Fig. 2) was as patchy as the early dis- tribution of D. ramosus . It has been observed exclusively in or near towns and usually low in numbers (max. 2 individuals per one hour of search). Discussion Only since the early 1990s are the data about the occurrence of the two species of sufficient quality to allow analysis of the routes and speed of distributional expansion. According to its distribution before arriving in Denmark, D. ramosus must have come from the Benelux/western Germany area. At the subcontinental (north European) scale, there is some evidence of a dispersal front (Netherlands 1993, Germany 2002, Den- mark 2007, Sweden 2012), but at the national Danish scale this disappears completely.The map of its occurrence in 2010 (Fig. 1A) indicates that neither distance nor sea water were barriers to dispersal. The species was soon found at locations far apart over most of the country, but at the same time it was missing in large areas. Such a distributional pattern signifies long-distance jump dispersal from the source area(s). Multi- ple independent immigrations from abroad represent a likely scenario and are compatible with the most probable mode of dispersal, i.e. transportation by human traffic (Noordijk et al. 2007, Vestbo et al. 2018). In fact, Fig. 1A may allow us to hy- pothesize in more detail about how this transportation took place. The occurrence in eastern Jutland, Funen and Copen- hagen fits a pattern of immigration via the Danish highways, which extend the north German highway system northwards along the east coast of Jutland with a branch going east over Funen and Zealand to Copenhagen and Sweden, all of which are connected by bridges. Specifically, the first Danish records of D. ramosus (and also O. spinosus , Fig. 2) were from Årslev on the island of Funen (Fig. 1A & 2). Vestbo et al. (2018) Fig. 2: Known distribution in Denmark of Odiellus spinosus at the end of 2017. Star indicates point of first Danish record (2006). Closed circles: O. spinosus present. Open circles: localities searched, but O. spinosus was not found. For names of Danish regions/islands, see Fig. 1A Fig. 3: Increase in the number of localities from which Dicranopalpus ra- mosus ( A ) and Odiellus spinosus ( B ) have been reported to Naturbasen (2018)