Tachinid flies are mostly robust flies with spiny abdomens. This group lacks spines on the abdomen, with Gymnosoma meaning “naked body.” Adults sip nectar from flowers, but larvae prefer protein. Of the 1,345 species of tachinid flies in North America, larvae are almost exclusively internal parasitoids of other insects, especially caterpillars. Typically, the females lay eggs on the host, and the larvae burrow inside. They feed within the host, avoiding vital organs until the last stage of their own development (usually killing their host). Hosts for this genus include adult and larval stink bugs and shield bugs (Pentatomidae). 

Size: 8 – 10 mm

Photos by: Connie Geiger on 8/20/22 in Helena, MT