In this study we investigated the ability of females of the spider wasp, Pepsis thisbe, to detect and respond to chemosensory cues associated with two species of theraphosid hosts (Aphonopelma moderatum and A. texense), as well as a novel chemical cue associated with a stored grain beetle (Tribolium confusum), a species not likely to be encountered by these wasps. Field-collected adult wasps were subjected to choice experiments where they were exposed to a piece of filter paper conditioned with one of these treatment cues versus one sprayed with water (control). One half of the floor of a test chamber contained the treatment cue, while the other contained the control paper. For each trial, the amount of time spent on each paper was recorded. Wasps spent significantly more time on paper conditioned with chemical cues associated with A. moderatum than they did on paper conditioned with cues from A. texense or T. confusum. In addition, field data collected at the study site in southern Texas (Zapata County), showed that over 91.2% of all P. thisbe larvae were found attached to A. moderatum as compared to only 8% for A. texense, despite the fact that the abundance and size of these two theraphosids were similar. Eighty-one percent of all paralyzed A. moderatum found with wasp larvae attached to their bodies were females.