Novel nesting of ants in bee cocoons in empty shells of terrestrial gastropods

Several species of ants were reported to place their nests inside empty shells of larger terrestrial gastropods. The structure of their nests was never studied in detail. We recorded 14 species of ants nesting in empty shells of terrestrial gastropods in various habitats of the Czech Republic, of which especially small species of the genus Temnothorax were the most numerous. In steppic habitats, nests of Temnothorax unifasciatus were placed inside the cocoons of the shell-nesting solitary bee Osmia bicolor in several cases. This bee is a specialist for nesting inside empty shells and is locally common and numerous in steppic habitats in Central Europe. In two nests, remnants of a dead bee were found inside the cocoon, together with the colony of T. unifasciatus. The adult of O. bicolor probably died inside the nest and was partly eaten by the ants suggesting a scavenging behaviour. This finding is unique and interesting, brings new insight to the biology of ants and a challenge for further studies on ants nesting in empty shells of gastropods.