Ground dwelling insects

I was planting sunflowers and nasturtiums by the foundation of the house when a medium-sized bee started snuffling around some holes in the ground. I got nervous that I'd disturbed her home, because 70% of native bees are ground nesters.
Two years ago, I had no idea native bees even existed. Turns out there are about 4,000 species native to North America and honey bees are not one of them. Honey bees come from Europe and Africa. Ground-nesting bees tend to like sandy soil, on slopes especially, so if you see perfectly round holes in the soil, that's likely who is living there. 
Try looking at the ground while you walk around an open area. You'll probably see some bee homes. Oh, and very few of our native bees sting; they're just too small. Bumblebees do, of course, but only if they're forced to. 
The ground is quite a dangerous place to live nowadays. All insects that live there, including fireflies, are very vulnerable to the pesticides and chemicals we put on the ground. A conventional lawn will have very little insect life. Even in organic yards, they are at risk of being dug up.  We've been doing so much yard work that we've unearthed two of these bees that I know of. I also accidentally dug up the larvae of something that was nearly formed but still translucent white. 
So be careful when you're digging. If you see round holes where you'd like to dig, choose something else to do. I routinely do this, which is sort of inconvenient, but I think it's a necessary mindset shift. I don't need to dig in this one spot more than a creature needs its life.