We report on efforts to maintain two common sphecid wasps, Chalybion caeruleum (Saussure 1867) and Sceliphron caementarium (Drury 1773), in field and laboratory enclosures in order to observe their predatory interactions with the orb-weaving spiders Argiope aurantia Lucas 1833 and A. trifasciata (Forskål 1775). Both species of wasps seemed to locate webs primarily by chance while flying along the tops of the vegetation but differed greatly in their hunting tactics once webs were located. Sceliphron caementarium was most successful at capturing spiders that had dropped out of webs in response to the wasp's hitting the web. But, C. caeruleum often employed a type of aggressive mimicry: it landed in the web or used its middle legs to pluck the web, luring the spider to the wasp. Argiope did not differ in their defensive response to C. caeruleum and S. caementarium. Most Argiope dropped out of webs in response to attacks rather than using other defensive behaviors such as shuttling between sides of webs or vibrating webs.