Although spiders are predators, they are themselves preyed upon by mud-dauber wasps (Sphecidae). Spiders’ web architecture is considered to be defensive against wasp predation, with three-dimensional (3D) webs thought to provide more effective physical barriers than their ancestral two-dimensional (2D) webs. We examined whether a) 3D webs act as barriers to Sceliphron caementarium wasp attacks relative to 2D webs, and b) spider chemical cues mediate wasps’ prey recognition and discrimination.
Mud-dauber wasps captured Larinioides sclopetarius (Araneidae, 2D spider) but rejected Parasteatoda tepidariorum (derived araneoid, 3D spider), with or without their webs. Our results suggest that mud-dauber wasps choose spiders based on chemical cues, rather than web architecture. These results were consistent across four other araneid and four other derived araneoid spider genera as well. We found that wasps rejected hexane-washed 2D spiders, indicating that a cuticular chemical cue is necessary for prey recognition. Moreover, when we offered individual wasps a choice of paper balls treated with cuticular extracts of 2D spiders, 3D spiders, or hexane controls, the wasps spent significantly more time antennating 2D-spider-extract-coated balls. Analysis of cuticular extracts of four 2D and four 3D spider genera by Gas Chromatography/ Mass Spectrometry (GC/MS) revealed that while chemical profiles of 2D spiders were dominated by branched hydrocarbons, those of 3D spiders contained primarily esters of fatty acids. These results provide the first evidence that spiders’ cuticular cues mediate prey recognition by sphecid wasps.