This paper presents the results of the one-year field research into the hoverfly (Diptera: Syrphidae) in Mareschi, in Sant’Antonino di Susa municipality. The sampling activities were performed with Malaise trap, emerging trap, and entomological net. Monitoring was carried out from March to October 2018 in the over-mature alder forest, classified under the Natura 2000 Habitat code 91E0, considered as a priority in EU 92/43 Habitats Directive. Preliminary data from July to October 2017 are also included. Overall, 74 species were recorded, with the first records of 7 species for Piedmont. Some of the observed species in Mareschi are of primary conservation importance, such as Arctophila superbiens (Müller, 1776), Sphiximorpha subsessilis (Illiger in Rossi, 1807) and Temnostoma bombylans (Fabricius, 1805). The use of Syrph the Net analysis and the comparison with other woods in Po Plain confirm the high naturalistic value of the studied area.