Monte delle Formiche is situated between the valleys of the Idice and Zena rivers, about 30 km south of Bologna, and it is the highest peak within the Pianoro municipal territory (638 m s.l.m.).
Its name derives from a very particular phenomenon: every year, since ancient times, swarms of male winged ants of the variety of Mirmyca Scabrinodis have migrated to this summit in the early days of September to complete their nuptial flight. After mating, hundreds of thousands of ants go to die in the area of the sanctuary. It is a truly unique spectacle: you can see black clouds of ants descending from the sky to die all together.
It is still not clear from a scientific standpoint why this happens. It is perhaps because of this veil of mystery that over the centuries the phenomenon has come to be associated in popular tradition with September 8, the Nativity of the Blessed Virgin Mary, though in reality the exact day can vary based above all on climate conditions.