My great grandfather was an immigrant to the USA in 1907 but wasn’t a citizen yet so couldn’t enlist. He went back to Italy to fight in the war. He was from Sellia Marina. From the research I’ve done, I take it he was some sort of officer? But the story in the family has always been that he fought against Mussolini. I don’t know how this could be since that didn’t happen until WWII? All of his sons were in WWII but no info on if at 56 he was but he was a citizen in 1921 so would he still have been in Italian Army? Very confusing because no one knows anything in this family.
He was definitely a member of the regular troops as the officers' uniforms had pockets in the front and were slightly different in the design.
Very good article on ww1 Italian uniforms (in Italian)
The insignia is so dark that could be black indicating both an artillery or an engineer regiment, the only difference being the border color (yellow for artillery and red for engineer).
List of WW1 Italian regiments with insignia
I excluded the special department of the Arditi (which also had a black insignia) because the uniforms were very different from the one shown in the photo.
The hat is the only element that could clarify the actual collocation but unfortunately the photo is not very clear and both regimets have very similar emblems.
If the elements in the lower part of the hat correspond to two cannons, we certainly have an artillery man. If instead they correspond to two crossed halberds we have an engineer.
On his left hand cuff we can see his rank, being Maresciallo di Compagnia indicating that the photo might be of 1916 as the same rank in 1915 had a different design and was replaced in 1917 by the new ranks of seargeants
To me they look more like halberds, so my final verdict will be an engineer