I encountered a number of these flies in a wooded area at Kickapoo State Park this afternoon. Larvae are predaceous. The adults are present during the spring and early summer in wooded areas with lush undergrowth. Diet is unclear. Some think adults may not eat at all.
It’s odd that I’ve never seen them before. I guess in the past most of my arthropod-related activities have taken place during the summer and fall. It’s nice to find surprises in quantity!