A comparative inventory of arachnids (spiders, scorpions, pseudoscorpions and harvestmen) collected on Porquerolles and Port-Cros (Var), from 1993 to 1995, showed a fairly high species diversity, with 156 and 138 species, respectively, identified from these islands. The spider family Linyphiidae is not considered. The strongly degraded shore habitats at Porquerolles have lost most of their spider species and one harvestman species is in danger of disappearing completely. Cultivated areas are poor habitats for arachnids or are invaded by a few species known to be widely distributed in Europe. Leaf-inhabiting spiders are dominant in terms of number of species and individuals. Lapidicolous and corticolous species are well established in woody areas, the soil of which retains some moisture. Moist microhabitats, which favour populations of some species, are also produced in the vicinity of orchards and crop fields, where watering is carried out, and around the water purification station at Lagunes. Species "new "for the island (80)have probably been introduced passively, with the influx of tourists and goods from the continent, which has greatly increased in recent years. In Port-Cros, vigilance at the National Park, a smaller number of tourists and the absence of cultivated areas have created a different situation.Microhabitats are drier and less varied than in Porquerolles. Quite large populations of heliophilic spiders are established on all types of foliage. Lapidicolous and corticolous spiders are not abundant, but a typically Mediterranean species of ground-living mygalomorph is common over the whole island. The scrub which has developed in Bagaud ("Réserve intégrale") shelters a fairly high diversity of spider species, some of which are not found on Port-Cros itself. The diversity of arachnids on Port-Cros seems to have decreased in the past sixty years. Moreover, the dryness of the habitats and conserving action of the National Park have resulted in large populations of spiders belonging to a limited number of species. Some harvestmen and pseudoscorpions appear for the first time in this inventory.
Hyères Islands, Mediterranean, Port-Cros, Porquerolles, comparative fauna, Arachnida, human impacts.