Among the 1590 terrestrial arthropod species alien to Europe identified in this book, 78 were selected to produce specific factsheets in order to provide more information on their biology, distribution and impact. We included two more species which are alien in Europe, the horse-chestnut leaf miner (Cameraria ohridella) and the African cotton leafworm (Spodoptera littoralis) because of their importance.

These 80 species are perhaps not the most important alien invaders, but they are rather representatives of the main taxonomic groups of alien terrestrial arthropods. They were selected so as to represent different pathways of introduction and diverse impacts on ecosystems, economic activities and human and animal health. These species include two myriapods, one spider, one mite, 18 coleopterans, seven dipterans, 23 hemipterans, 10 hymenopterans, one termite, 14 lepidopterans, and three thrips. Each factsheet includes information on the following aspects:

Description and biological cycle: A brief description of adults and immature stages is given, whenever possible illustrated by a photograph, to help the reader identify the species. Further information details the general characteristics of the biological cycle in the invaded area, especially the species' potential to reproduce and the hosts it has colonized.

Native habitat: The factsheet includes the habitat type where the species is found in its native range. In order to make habitat types comparable among taxa, we adopted the classification of the European Nature Information System (EUNIS) database (http://eunis.eea.europa.eu). The habitat type codes are detailed in Appendix II. When information was available, we included specific habitat requirements which may help understand the potential of the species to establish and spread in Europe.

Habitat occupied in invaded range: The different habitats colonized by the alien species are described as for native habitats.

Native range: The native distribution of the species is described. For some species, there is very precise information available, but for others, only brief details of a region or even continent can be given.

Introduced range: The date of the first record in Europe and the location of this record is given, as well as details of the process of dispersion in the continent when available. A distribution map is supplied for all species. For most of them, presence/ absence data have been obtained only at country level, but for a few species, more detailed maps are given to show the distribution at regional scale. However, the missing occurrence of species from some countries does not always mean that these countries are not colonized, but may rather result from a lack of data for the country concerned. The map also indicates eradication records where relevant.

Pathways: We included information on the routes of introduction to Europe, and the potential of the species to disperse within the continent once it has established.

Impact and management: This section details the importance of the species' impacts in the colonized habitats. Both ecological and economical impacts are detailed when known. Practical advice where known is given regarding mechanical, chemical and biological control methods.

Selected references: Three of the most relevant references to the history of the species' introduction and spread in Europe are given.