Introduction, establishment rate, pathways and impact of spiders alien to Europe

A comprehensive analysis of spiders reported as alien for Europe over the last 200years has yielded information for 184 spider species, which had been introduced at least once. The most common spider families are Theridiidae (27 species), Pholcidae (15), Salticidae (14), Sparassidae (14), Ctenidae (14), and Theraphosidae (13) but overall establishment rate was only 28%. No ctenids or theraphosids established, and only one sparassid species, but many theridiids and pholcids. Most introduced species originated from South (34%), Central (10%) or North (12%), America, Asia (19%) and Africa (15%). Only few of the South and Central American species could establish, while species from North America (36%) and Asia (63%) had much higher establishment rates. Over the last 200years, introduction and establishment rates have been strongly increasing. Three pathways are responsible for the majority of introductions: fruit shipments (67% of all cases), potted plants (16%) and containers or packaging material (12%). In contrast to fruit shipments, spiders introduced on plants or with containers have high establishment rates (65 and 47%). Environmental impact of alien spiders can be expected on both insects (through predation) and spiders (through predation and competition), potentially leading to change of species composition and guild structure. Socio-economic impact includes reduction of marketability of horticultural products through excessive spinning activity which also may cause increased cleaning costs at facades and windows. Impact on human health may be caused by bites and subsequent need for medical treatments. For all these impact categories, however, only anecdotal evidence is given for alien spiders in Europe. This may change when spiders of medical importance such as the frequently introduced Latrodectus species will establish. Considering the current trends it is concluded that introduction and establishment rates of alien spiders will strongly increase in the next years unless preventive methods become more efficient