Abstract
Various nesting conditions of a spider wasp Episyron arrogans were examined in the context of the encounter and avoidance in the host-parasite relationship with a miltogrammine fly Metopia sauteri. When the wasps spent more time in nest burrowing and prey transporting, the nests tended to be more frequently found by the hole searching flies. The time spent in nest burrowing was principally influenced by the relative size of hunted prey to the wasp and the soil conditions of the burrowing site. That is, the wasp, which hunted the relatively small sized prey and/or preferred the sandy ground as burrowing site, reduced the chance of encounter with the flies. Furthermore, when the fly approached the nest the wasp frequently abandoned the burrow, and moved to a parasite-free site carrying the hunted prey. In the nesting behaviour of this spider wasp, there is no remarkable modification, like as 'anti-parasite adaptation' hypothetically pointed out in the sphecid digger wasps. The simple and primitive manner, that is, the wasp burrows after hunting a prey, seems to make the wasp less vulnerable to such cleptoparasites.
