Photo 1: Fungus killed flies on grape. Despite any circumstantial evidence, they are incapable of damaging plants.
This fungus has been particularly common this year due to the abundant rainfall we have experienced throughout much of Minnesota. When seed corn maggot flies become infected with this fungal disease, they usually fly to a plant or other object and climb up. Eventually they die, leaving their legs and wings in whatever position they were in at the time of death. Additionally, their mouthparts are often extended out. In recently infected flies, the abdomen is swollen and whitish, with fungus protruding between the body segments.
When these flies die on a plant that is damaged, it seems reasonable to blame them for this injury. However, seedcorn maggot flies do not feed on plants (in fact there are no adult flies in Minnesota that directly feed on plants). They are just a curiosity and should be ignored.