Observations on the parasitation of orb-weaving spiders (Araneidae) by Polysphincta rufipes (Hymenoptera: Ichneumonidae)

We found the ichneumonid Polysphincta rufipes Gravenhorst, 1829 (tribus Polysphinctini) to be a koinobiont parasitoid of two species of araneid orb-weavers, Larinioides sclopetarius and Zygiella x-notata, in Central Europe. Some notes on the biology of P. rufipes are given, based on observations both in the field and in the laboratory. The wasps directly attack non-adult spiders sitting in the hubs of their webs. Parasitized spiders could be found from, at least, August to early December. The duration of the development of the wasp larvae, including the pupal stage, is about two months. It seems conceivable that at the end of the larval stage the larva somehow manipulates its host spider; i.e. the spider is forced to enter its retreat – a safe place where the larva can kill the host, complete its development and spin a cocoon for pupation (pupa libera).