This flattened-looking beetle is called a Hermit Scarab Beetle (Osmoderma subplanata); They are sometimes called Odor-of-leather-beetle due to the fact that they give off an odor of Russian Leather. They grow to about 2 inches in length and are a beautiful dark chocolate brown.
They feed on decaying vegetation and fruit. This one was photographed last year on a pumpkin vine in my moms backyard. It apparently was feeding on the pumpkin vine. They are slow moving and easy to photograph. These are a perfect insect to use with children, they aren't intimidating, they are slow moving, and will not bite.
There isn't much reported on them, but with the size of the beetle I would assume the grub would be quite large. Most likely they are like many scarab beetles and live underground or in decaying wood and feed on roots or wood.