Wasps of the Polysphincta clade are known to manipulate the behavior of their web-building spider hosts by injecting psychotropic chemicals, but the methods they use to hunt spiders are poorly documented. In 25 attacks observed over several years in the field in the Valle Central of Costa Rica, Polysphincta gutfreundi showed great flexibility. Wasps employed three basic hunting tactics to subdue the host spider Allocyclosa bifurca: strike the spider at its resting site at the hub of its orb web; land in the sticky spiral of the web, struggle, and then attack the spider when it approached; and wait immobile at the hub to await the return of a spider that had fled. The wasps moved and oriented agilely on their hosts' orbs. The only repeatedly effective spider defense was to drop immediately from the web and remain away for many minutes. Parasitism was strongly clumped spatially, suggesting that female wasps may learn where to hunt. Nearly all the details of P. gutfreundi attack behavior have also been observed in other species of the Polysphincta clade. They include the use of multiple attack strategies, surprise attacks from the air on spiders resting on their webs, attacks through the hub, agile movements on the spider's web, inducing the spider to approach by apparent imitation of prey, waiting for long periods in the web poised to strike, and inserting the ovipositor into the anterior end of the spider's cephalothorax. One unique detail of attack behavior in P. gutfreundi was to shuttle rapidly to the other side of the hub to reach the spider. Few of the spider's defensive traits were effective against these wasps. Species in the Polysphincta group are behaviorally flexible, but as a group these wasps utilize relatively uniform tactics to subdue their hosts.