(1) Background: Sceliphron is a genus of sphecid wasps that build mud nests for reproduction. These wasps prey exclusively on spiders, and commonly inhabit human constructions. The nesting behaviour and prey selection of many Sceliphron species are well studied, but despite being a common insect in urban areas, Sceliphron formosum has never been comprehensively studied. (2) Methods: In this study, over 650 mud nests of S. formosum were collected, analysed and examined to establish prey preference, nest ecology and interspecific interactions. Prey preference was evaluated in terms of abundance, diversity and morphology. Preference in terms of morphology was estimated using body length to leg span ratio (BLR). (3) Results: S. formosum largely preys on ground-hunting spiders, among which Salticidae represented the most collected prey. In terms of prey size, S. formosum captures prey with a large BLR. Moreover, an unexpected discovery showed that the enclosed mud nests provide a micro niche that supports a wide variety of insects. Sixteen families and 23 species of insects were found associated with the use of mud nests, comprising the insect orders Hymenoptera, Diptera and Coleoptera. These included important pollinators, new species and native species not recorded in the past 20 years of mud dauber wasp research. We propose the potential of S. formosum as a keystone species, due to its ability to provide a micro niche for native species in urban areas. We also discuss how these results contribute to our knowledge on the role of insects in urban ecosystems and their significance in relation to conservation, ecology and biodiversity studies.
Keywords: Salticidae; Sceliphron formosum; Sphecidae; mud dauber wasps; nest ecology; parasitoids; prey preference.