Hooiwagens op een Nijmeegse muur

The results of a year-round inventory of Opilionids on a long wall in Nijmegen, the Netherlands, are presented. From January 2005 to January 2006 the site was visited once or twice a week, 92 times in total. Seven species of harvestmen were found: Phalangium opilio Linnaeus, 1761 (a total of 31 specimens), Opilio canestrinii (Thorell, 1876) (479), Oligolophus hanseni (Kraepelin, 1896) (23), Paroligolophus agrestis (Meade, 1855) (162), Odiellus spinosus (Bosc, 1792) (1), Dicranopalpus ramosus (Simon, 1909) (186) and Leiobunum rotundum (Latreille, 1798) (1). A large amount of specimens (75%) belonged to Dicranopalpus ramosus and Opilio canestrinii, both recently arrived in the Netherlands. Opilio parietinus (De Geer, 1778) seemed to have been completely “replaced“ by Opilio canestrinii. It is suggested that Leiobunum rotundum competes with Dicranopalpus ramosus, explaining the rare incidence of the first mentioned species on the investigated wall. Due to the mild weather conditions during the winter early 2005, some adults of both Dicranopalpus ramosus and Opilio canestrinii could survive well up to 25 February and 3 February, respectively.