Notes on the Biology and Host Ant Speciicity of the Myrmecophilous Syrphid Fly Microdon major (Diptera: Syrphidae), a Social Parasite of Formica Ants (Hymenoptera: Formicidae) by Authors: Magdalena Witek 1 *, Dario Patricelli 1 , Luca Pietro Casacci 1 , Francesca Barbero 1 , Emilio Balletto 1 & Simona Bonelli 1 ABSTRACT Many species of social parasites are rare and endangered and knowledge of their interaction with hosts is oten scarce. his is particularly true for Microdon syrphid lies, many of which are obligate social parasites of ants. Since cryptic speciation is common in social parasites, the precise number of Microdon species is unknown and only a few apparently exist all across Europe. Here we present data on the host ant speciicity, larval behavior and habitat preferences of Microdon major. his species was considered as a sibling species of M. analis by Schmid (2004) mostly on the basis of some morphological diferences between pupae and diferent host ant use. In this paper we report the irst Italian record of M. major. Larvae and pupae of this species were found in two nests of Formica lemani and in one colony of Formica fusca. he three infested nests had been built under stones and fallen wood, and M. major instars were found in the wood debris, close to, or inside the brood chambers. M. major was found in sunny mountain meadows, surrounded by trees. On the contrary, M. analis is associated with Lasius ants and occurs in more wet habitat, such as the “Molinietum”. During our ield survey we observed a small M. major larvae preying on ant brood. Only very limited information is available, however, on the habitat preferences and host ant speciicity of these Microdon species, and we stress the need to improve our understanding of their biology before we can draw appropriate schemes for the conservation of these rare social parasites, as well as for gaining a more complete understanding of their taxonomy. 1 University of Turin, Department of Animal and Human Biology, Via Accademia Albertina 13, 10123 Torino, Italy. *Corresponding author. E-mail: mawitus@yahoo.co.uk 1