Actually, it's a grub. I'd been finding these c-shaped white larvae every so often as I dug, and I wanted to find out what they were to see if I needed to do something about them. Turns out they're beetle larvae that usually prefer turf. I haven't found that many, so I'm not going to worry too much. I'll have to keep a lookout as the summer wears on, though.
I haven't used any pesticides so far, and I want to keep it that way as long as possible. Besides being distasteful, they're also another thing to keep track of and learn to use, and I hope to keep things as simple as possible.