Arachnologische Mitteilungen 57

28 T. Bauer, S. Bayer, E. Derschmidt & H. Höfer Nentwig et al. 2018).The record from Cologne is also, to date, the northernmost in its global distribution (Bauer & Grabol- le 2012). The southernmost record of P. maculatus currently known is from Israel (Zonstein et al. 2015). In Germany, Paratrachelas maculatus shows a distribution pattern similar to the Mediterranean invaders Zoropsis spinimana (Dufour, 1820) and Cheiracanthium mildei L. Koch, 1864 (Arachno- logische Gesellschaft 2018). The second record from Austria (Fig. 1) indicates a possible establishment in Vienna. In 2017 another specimen from Vienna was observed which could, based on its morphology, be identified as male of P. macu- latus ( https://forum.arages.de/index.php?topic=23427.0 ) , but unfortunately it was not collected. All records were made in autumn, which coincides with the typical phenology of the species (Kovblyuk & Nadolny 2009).The recent records from Stutensee-Blankenloch and the north of Stuttgart are the fifth and sixth in Germany (Arachnologische Gesellschaft 2018), while the record from Vienna was collected at exactly the same locality as another female in 2010 (Bauer & Gra- bolle 2012).We interpret our data (including a gravid female) as indication that the specimens collected in Germany and Austria originate from established populations, but additional records are needed to prove a (presumed) wider distribution in Austria. Notwithstanding the debate about whether European spider species should be seen as alien in other, formerly not colonized parts of Europe (Nentwig 2015, Nentwig et al. 2018), we decided to define P. maculatus as an alien species to Germany and Austria, similar to Mediterranean alien spe- cies included in the German checklist (Blick et al. 2016). In harvestmen (Opiliones), invading Mediterranean species are possibly responsible for the recent decline of several native species in urban areas of Central and Northern Europe (e.g., Toft 2018b).Therefore, the invasive potential of alien species from other parts of Europe should not be deemphasized by the usage of oversimplified definitions for alien spider taxa in Central and Northern Europe. Paratrachelas maculatus is associated with buildings and urban areas in Germany and Austria (and also in Italy and Slovenia; Hansen 1996, Kuntner 1997), while in Eastern Europe, the possible original distribution area, P. maculatus is common in a wide range of non-synanthropic habitats, e.g., sub-montane and montane forest steppes and forest planta- tions (Kovblyuk & Nadolny 2009). The occurrence in forest plantations could also have led to an inadvertent distribution of egg sacs or specimens with tree trunks or other plant ma- terial (potted plants). Currently, a preference for synanthropic habitats can be observed in the majority of non-native species in Europe (Kobelt & Nentwig 2008). On the other hand, a natural spread from Eastern Europe along river valleys, pos- sibly caused by climate change, seems unlikely at the moment. P. maculatus is currently not known from large areas of Sou- thern and Eastern Europe (Nentwig et al. 2018), although it was found in individual countries like Italy (Hansen 1996). The species was also recorded in Vienna,Austria and Cologne, Germany in two subsequent years (Bauer & Grabolle 2012). Both cities are separated by a linear distance of 750 km, which argues for long-distance jump dispersal due to transportation with traffic (see also Vestbo et al. 2018). A natural distribution from a population based on a single introduction into Central Europe is therefore implausible. A fast spreading invader like Mermessus trilobatus (Emerton, 1882), probably introduced in the 1970s to south-western Germany and mostly inhabiting natural and semi-natural habitats, needed about 30 years to reach the northernmost areas of Germany (Arachnologische Gesellschaft 2018, Nentwig et al. 2018). Egg sac and clutch With only 5–7 (large) eggs (Fig. 3), the documented egg number of P. maculatus is low compared to other non-native spider species in Central Europe, often producing dozens of eggs per egg sac (e.g., Miyashita 1987, Skow & Jacob 2003, Uhl 1998, Vetter & Rust 2012). Few large eggs per clutch could be evidence for a low reproduction rate and population density. Even in comparison with other Trachelidae the egg number is low. Trachelas volutus Gertsch, 1935, for example, a species only around 2 mm larger than P. maculatus (Plat- nick & Shadab 1974), produced 47–66 eggs (on average 56) in captivity (Amalin et al. 2001). Although egg number per clutch is generally related to body size and body mass of spi- ders (larger and heavier spider species produce more eggs per clutch; see Marshall & Gittleman 1994), several substantially smaller linyphiids like Oedothorax apicatus (Blackwall, 1850) are known to be able to produce more eggs per clutch than we have observed in P. maculatus (Holm 1940). On the other hand, a low reproduction rate could possibly explain the ra- rity of records of P. maculatus despite a relatively large known distribution area in Germany (and Central Europe). Interes- tingly, Bosselaers et al. (2009) mentioned that Paratrachelas ibericus (Bosselaers, 2009) is guarding its egg sac inside a sil- ken retreat, while the (camouflaged) egg sacs of P. maculatus were abandoned by the female. This could be an artefact of captivity, but the female was not disturbed several days before and after the egg depositions. The often observed polyhedral shape of (agglutinated) spider eggs was explained by Holm (1940) with a high degree of egg softness during oviposition, the subsequent drying of an oviposition liquid on the outside and the following agglutination of the eggs. The egg sac can be classified as type 4 sensu Austin (1985), consisting of very firm, thin and papery silk probably serving as a protection against scavenging predators like ants. Camouflaging an egg sac could be a reaction of a spider species to high parasitoid pressure. Species of Agroeca Westring, 1861 are known to ca- Fig. 4. Paratrachelas maculatus (Thorell, 1875), clutch of first egg sac built around 20.XI.2018. Scale = 1 mm