Now that the days of ice and snow are hopefully behind us, the activity of ground nesting bees has already begun to pick up in turf. These small solitary bees form small mounds of soil on the surface, generally in less thrifty areas where the turf is thin. The mounds of soil and the small bees flying in and out of the holes sometimes cause concern.
There are many species of ground nesting bees, and the date they emerge and become active can vary substantially with the type of bee and the geographic location of the site. Expect more activity as soil temperatures warm and other types of ground-nesting bees emerge.
These small bees won't sting, and will generally be gone in a few weeks. Chemical treatments are usually not necessary, but there are some options. Nonchemical deterrents include heavy watering, or tilling and heavy mulch in landscape beds.
For more information: BEES IN TURF.