Spiders associated with selected European hay meadows, and the effects of habitat disturbance, with the predation ecology of the crab spiders, Xysticus spp. (Araneae, Thomisidae)

In hay meadows near Zurich, central Europe, the faunistic composition of the foliage-dwelling spiders was evaluated using sweep-net technique. Eleven families were represented from the 1502 spider individuals captured, the majority of which (> 85%) belonged to the families Theridudae, Linyphiidae, Araneidae, Tetragnathidae, Lycosidae, Thomisidae and Salticidae. Of the adults collected (39 species, N = 203) 38% were orb-weavers, 33% were irregular or sheet-web weavers, and 29% were cursorial hunters. The crab spiders (Thomisidae), Xysticus cristatus (Clerck) and X. kochi Thorell, were the species most frequently collected. A low feeding frequency was observed in the field for the Xysticus spp. (<10% with prey, N = 395), and a wide variety of arthropod taxa was consumed by the crab spiders including eight orders of insects, other spider species and a representative from a family of earthworms. Although crab spiders have been noted as voracious predators of large social bees, this category made up only 3% (by number) of the prey. Previous reports found in the literature suggest that crab spiders that hunt on the flower inflorescence feed almost exclusively within a narrow range of pollinating insects, however, no supporting evidence for this contention was found, instead Xysticus spp. in European hay meadows are exceedingly polyphagous. The impact of mowing on meadow spider populations was evaluated using three methods, all yielding evidence that mowing had a negative effect on spider densities. Depending on the circumstances, the impact of mowing on spider densities in a diverse variety of meadows may range from mild to massive, however, emigration by spiders after their habitat has been disturbed, may serve as a beneficial arthropod generator, providing for the colonization of surrounding field crops. Zusammenfassung Spinnen in europaischen Mahwiesen: Artenspektrum, Einflus der Mahd und Pradatorenokologie der Krabbenspinnen, Xysticus spp. (Araneae, Thomisidae) Die Spinnenfauna von Mahwiesen wurde bei Zurich, Mitteleuropa, studiert. Insgesamt 1502 Spinnen aus 11 Familien (inkl. 203 Adulttiere aus 39 Arten) wurden mit dem Streifnetz gesammelt, wovon >85% den Familien Theridiidae, Linyphiidae, Araneidae, Tetragnathidae, Lycosidae, Thomisidae und Salticidae angehorten. Die netzlosjagenden Thomisidae [= Krabbenspinnen], Xysticus cristatus (Clerck) und X. kochi Thorell, waren die am haufigsten gesammelten Spinnen. Freilandbeobachtungen ergaben, das die Xysticus spp. sich von einem breiten Spektrum von Beutetieren aus den Taxa Diptera, Hymenoptera, Homoptera, Heteroptera, Thysanoptera, Coleoptera, Lepidoptera, Collembola, Araneae und Oligochaeta ernahrten (ausgesprochene Polyphagie), wobei <10% (N = 395) der im Feld angetroffenen Krabbenspinnen fresaktiv waren. Mit 3 verschiedenen Methoden wurde gezeigt, das die Mahd einen negativen Einflus auf die Populationsdichten von Wiesenspinnen ausubte. Wir vermuten, das die ausgedehnten Wiesenflachen innerhalb der mitteleuropaischen Agrarlandschaft eine wichtige Funktion als Pradatorenreservoir fur die Besiedlung von angrenzenden Ackerkulturen erfullen.