The nest of the mud-dauber wasp, Sceliphron spirifex (Hymenoptera, Sphecidae) : application of geological methods to structure and brood cell contents analysis

A collection of nests of Sceliphron spirifex from nine farms in Lombardy (Italy) enabled us to study their structure using a new approach involving some geological methods, and to add information regarding brood cell contents. Granulometric analysis revealed that the size of the particles used to build the nest does not depend on geographical location. The low amount of organic matter in the nest building material is inconsistent with the use of saliva, in contrast to a previous hypothesis. We identified micro-morphological homogenous zones in cell walls that represent the different sites where soil was collected by the wasps, which appear to be 3-4 for every nest. The method employed allowed us to confirm that the cells are built in a concentric way around the lumen. The prey content of each cell consisted of 6-14 spiders, belonging to four families; the largest number of prey species and the most abundant genera, Larinioides Caporiacco and Araneus Clerck, belong to Araneidae. Most prey were young individuals. The rate of parasitism, due to Diptera and Ichneumonidae, was generally high.