The ecology of selected species of spiders (Araneae), harvestmen (Opiliones), and the neglected tropical order Schizomida, alien to Europe, is discussed. Their geographic origins and pathways of introduction, by transportation with goods, are similar to other predatory terrestrial arthropods. Occurrence in buildings (synanthropy) is a prerequisite for range expansion in many arachnid species. Thelytokous parthenogenesis facilitated spread of a few spider, harvestman and schizomid species outside their native range. Both prey generalists and specialists (woodlice-eating Dysdera crocata and ant-eating Zodarion rubidum) are among species successfully expanding their range. Alien arachnids include individual species belonging to many different families. We stress the absence of true invasiveness of alien arachnids in Europe. Some unusual adverse effects of alien arachnids were recorded, such as pollution of buildings and clogged car fuel system ventilation tubes. Frequency of painful biting and threat to native biota are low.