My lawn is full of holes from bees burrowing into it. I'm concerned for my kids and pets, and I'm reluctant to mow. These are solitary ground nesting bees.
Solitary bees are much more docile than social bees.
That's because social hymenoptera colonies have only one individual, the queen, who lays eggs. She's usually deep inside the colony where you can't see her, and she is well protected. Other individuals are workers, and they will defend the nest, even at some risk of being killed in the process, because they are expendable. They can sting, but generally only do so if you pick them up or step on them or something drastic. You may see some bees hovering over holes, and others actually entering the holes.