The foliage-dwelling spider community of an abandoned grassland ecosystem in eastern Switzerland assessed by sweep sampling

The foliage-dwelling spiders of an abandoned grassland ecosystem (Valeriano-Filipenduletum, Carex acutiformis Ehrh. type) in eastern Switzerland were studied from June to September by sweeping technique. A total of 632 adult specimens representing 22 identified species has been collected by sweeping (based on totally ca. 2000 single sweeps). More than two thirds of the sampled adult spiders were females. At all times, more immature than adult spiders were captured (overall, 83% immatures). Among the 3756 collected spiders (immatures plus adults), the six families Agelenidae, Araneidae, Micryphantidae, Pisauridae, Salticidae, and Tetragnathidae prevailed in the sweep net samples (combined ca. 90% of all spiders). The five speices Eyarcha arcuata (Clerck), Hylyphantes nigritus (Simon), Neottiura bimaculata (L.) Pisaura mirabilis (Clerck), and Tetragnatha extensa (L.)constituted combined > 80% of all adult spiders sampled by sweeping. The web-building spiders T. extensa and H. nigritus were the two species most frequently captured. Adults of large orbweaving spiders (Argiope bruennichi [Scopoli], Araneus quadratus Clerck, and Araneus diadematuss Clerck)were abundant in the investigated grassland habitat (assessed by web counts), but obviously underproportionately represented in the sweep net samples. Considering the total number of spiders (imatures plus adults) per 100 single sweeps, a strong increase from spring to late summer was noticed which is considered to be primarily due to egg-laying of them most dominant species in spring followed by hatching of the spiderlings in the course of the summer. Since spiders are abundant predators in this grassland ecosystem (ca. 0.1 m2 web area/m2 ground area, alone due to orb-weavers in August/Sept.), they may be important mortality agents of grassland arthropods.