When you see something like this small mound of sand, with a single, perfectly round hole in the middle of it, in the center of your lawn, what do you think?
Nope. Not even close. It was many years before I realized what I was actually seeing. Mounds like this are the work of solitary bees, those wonderful little pollinators that most of us barely even know about. As I walk around my neighborhood, I see quite a few of these tiny sand piles right now - but only in the yards where the grass is just so-so. Thick, lush lawns - which can only be maintained through chemicals down here - have absolutely no little bee mounds.
So, wouldn't ground-nesting bees be a bad thing? What about the possibility of bee stings?
You don't have to worry at all. There's really no problem. The key word is SOLITARY. Each hole is the work of one little female bee, who visits hundreds of flowers to collect pollen with which she makes little balls of food, one ball per egg. She will only produce a couple dozen eggs in her lifetime - and she'll work VERY hard to do that and to provision each one with enough food to ensure survival. This little bee doesn't have time to worry about keeping anything away from her nest. In fact, you'll rarely catch her there. If she were to sting you, she'd die - and then there would be no more eggs laid. She's not going to waste her life that way.
Native solitary bees are the pollinator workhorses of this continent. They evolved with the plants on North America to efficiently pollinate their flowers, producing fruit, nuts, and seeds. (Honeybees were brought over by European settlers. The native plants here would survive just fine without honeybees.)
Right now, in very early March, I'm only seeing one species of solitary bee at flowers. As I look around, I'm also only seeing one type of solitary bee nest, consisting of this dainty mound of fresh sand with a perfectly round hole, about 1/4" in diameter, in the approximate center of it. I have not yet seen a bee come out of one of these holes, but I am guessing that the two belong together, that these are the nests of the bees that I'm seeing.
Although these bees are primarily known for "working" blueberry flowers, I am also seeing them at both azalea blooms and at spiderwort blossoms. Here's a female with legs full of (white) pollen at a spiderwort bloom.