Arachnologische Mitteilungen 56

Arachnologische Mitteilungen / Arachnology Letters 56: 1-5 Karlsruhe, September 2018 During several decennia, Northern Europe has witnessed re- peated invasions of harvestman species originating from the Mediterranean region (Wijnhoven et al. 2007, Enghoff et al. 2014). Coming from Italy, Opilio canestrinii (Thorell, 1876) expanded through Central Europe during the 1960s, 1970s and 1980s (first records in European countries summarized by Vestbo et al. 2018). In those days, few people paid atten- tion to harvestmen; therefore, observations are generally too haphazard to reflect the true routes and the speed by which the species expanded. For example, when discovered in Den- mark in 1987, it was already of nation-wide occurrence and the second most abundant species in urban habitats (Enghoff 1988). It was clear, however, that the species had expanded very fast, but exactly how fast was impossible to tell. When other species followed suit during the 1990s and 2000s, the arachnological community was better prepared and could further take advantage of the creation of national public data- bases on the internet into which gifted amateur naturalist re- port their observations. This has tremendously enhanced the ability to follow fast faunistic changes, even if attention is not specifically directed towards harvestmen. Dicranopalpus ramosus (Simon, 1909) originated from the Iberian Peninsula and Morocco (Wijnhoven & Prieto 2015). It turned up in southern UK in 1957 and slowly widened its distribution along the southern British coast (maps in Sankey & Savory 1974, Rambla 1986). Its northward expansion in western Europe became clear during the 1990s when it was recorded from the Netherlands (1993), Belgium (1994), Ire- land (1994) and Scotland (2000) (summarized by Noordijk et al. 2007). In 2002 it was recorded from Germany (Schmidt 2004), in 2007 from Denmark (Toft & Hansen 2011), in 2012 from Sweden ( Jonsson 2013) and in 2014 from Poland (Rozwałka & Rutkowski 2016). Noordijk et al. (2007) com- mented on the speed of spreading as the species was found in most parts of the Netherlands only 14 years after the first record. Based on a nation-wide survey of urban areas in 2010, Toft & Hansen (2011) reported on the early colonizati- on and establishment in Denmark. They found that already within three years after the first discovery of the species it had reached most parts of the country, even locations as far from the presumed sources of immigration as is possible in Denmark. If these observations reflect the process of invasion correctly (see below), they underscore that the species was ex- panding extremely fast. The present paper follows up on the previous study (Toft & Hansen 2011). A new nation-wide survey was conducted in 2017, i.e. 10 years after the first Danish record of D. ra- mosus with the purpose of recording the changes that have occurred in the Danish distribution of D. ramosus during the intervening seven years. The combined data is then used to deduce the most likely routes and the most likely mechanisms of dispersal by which the species has colonized and establis- hed itself in Denmark. Odiellus spinosus (Bosc, 1792) is another newcomer in Denmark, noticed for the first time in 2006 (Enghoff & Pe- dersen 2007) and also recorded during the urban surveys. It is native to southern and western Europe (Italy, northern Spain, France, Benelux and southern UK) (Martens 1978). Since the 1970s it has shown expansive tendencies by widening its area eastwards in Germany (Arachnologische Gesellschaft 2018) and adjacently Poland (Rozwałka et al. 2013).The species has spread in Denmark during the same period as D. ramosus al- lowing a direct comparison between the two with respect to area occupied and the speed of colonization and spreading. The results are discussed in terms of two models of expan- sion (Hengeveld 1989): wave front expansion or jump disper- sal. Either a species enlarges its range as a broad moving front progressing wavelike into the new range. Expansion happens Ten years after the invasion: Dicranopalpus ramosus and Odiellus spinosus (Opiliones, Phalangiidae) in Denmark Søren Toft doi: 10.30963/aramit5601 Abstract. The two harvestmen Dicranopalpus ramosus and Odiellus spinosus were first recorded from Denmark in 2007 and 2006, res- pectively. Two nation-wide surveys of the species in urban habitats were conducted in 2010 and 2017 providing information on their initial colonization and subsequent establishment and spread. By 2017, D. ramosus occurred in all parts of Denmark and was a frequent and abundant species in most of Jutland. On the Danish islands, the species was present but much less frequent. Odiellus spinosus occur- red sporadically in eastern Jutland and more frequently on the islands. During the early years, new records of both species came from spaced-out locations, indicating arrival by long-distance jump dispersal possibly by independent colonisations from abroad and most probably mediated by human traffic. The range expansion of D. ramosus in northern Europe has occurred with a speed of 35–100+ km per year. Keywords: alien species, colonization, introduced species, invasion routes, speed of range expansion, urban species Zusammenfassung. Zehn Jahre nach der Invasion: Dicranopalpus ramosus und Odiellus spinosus (Opiliones, Phalangiidae) in Dänemark. Die beiden Weberknechtarten Dicranopalpus ramosus und Odiellus spinosus wurden 2007 bzw. 2006 erstmals in Dänemark nachgewiesen. In den Jahren 2010 und 2017 wurden zwei landesweite Kartierungen beider Arten in städtischen Lebensräumen durch- geführt und erbrachten Kenntnisse zur Kolonisierung, Etablierung und Ausbreitung der Arten. Im Jahr 2017 kam D. ramosus in allen Teilen Dänmarks vor und war in weiten Teilen Jütlands stetig und zahlreich zu finden. Auf den dänischen Inseln war die Art präsent aber weit weniger häufig. Odiellus spinosus kam im Osten Jütlands nur sporadisch vor und war auf den Inseln häufiger. Während der ersten Jahre wurden beide Arten an weit voneinander entfernten Orten gefunden, was auf Ausbreitung aus großen Entfernungen hindeutet, möglicherweise unabhängig voneinander aus dem Ausland mithilfe des menschlichen Fernverkehrs bzw. Gütertransportes. Die Erwei- terung des Areals von D. ramosus in Nordeuropa fand mit einer Geschwindigkeit von 35–100+ km pro Jahr statt. Søren TOFT, Department of Bioscience, Aarhus University, Ny Munkegade 116, DK-8000 Aarhus C, Denmark; E-mail: soeren.toft@bios.au.dk submitted 3.3.2018, accepted 23.5.2018, online 28.6.2018