Ants that regularly include seeds in their diet are called harvester ants. Harvester ants are not a monophyletic group: feeding on seeds is found in numerous species of the subfamilies Ponerinae, Myrmicinae and Formicinae (Holldobler & Wilson, 1990). The ants of the genus Messor (subfamily Myrmicinae) belong to the best-known harvester ants. They are mainly granivorous, but their diet may include also dead and living insects and other proteinic food, such as snails and pieces of flesh of dead mammals (Cerda & Retana, 1994; Gillon, Adam & Hubert, 1984; Hahn & Maschwitz, 1985; Lopez, Serrano & Acosta, 1992; Sheata & Kaschef, 1971).