I think I've finally figured it out -- these little beasties are rose chafers, or Macrodactylus subspinosus!
According to Jeffrey Hahn, Associate Professor in the Department of Entomology at the University of Minnesota:
• An adult rose chafer is a moderate-sized insect, slender, pale green to tan in color with reddish‑brown or orangish spiny legs and short antennae.
• The larval stage, or grub, has a brown head and conspicuous legs and its body is bent into a ‘C’ shape. Fully grown, a rose chafer larva is about 3/4-inch long.
• Adult rose chafers feed primarily on flower blossoms, especially roses and peonies, causing large, irregular holes. They also damage fruits particularly grape, raspberry, and strawberry.
• Rose chafer also feed on the foliage of many trees, shrubs and other plants, such as rose, grape, apple, cherry, and birch. Rose chafers typically damage leaves by eating the leaf tissue between the large veins, a type of injury known as skeletonizing.
Now that I know what they are, I can figure out what to do about them! Stay tuned!