"Mining bees" are an occasional pest of the lawn, especially dry areas with sparse vegetation. Not every entomology reference uses the nickname "mining bee;" a more commonly used name for these solitary, ground-nesting insects is andrenid bees.
The name "mining bee" however, accurately describes their underground nesting habit. The bees nest in the ground in cylindrical tunnels dug by the females. A large group of bees frequently nests in a small area of the lawn, as mentioned, in an area where the grass or ground cover is thin. Entrance to the tunnels is marked with small piles of soil. The hole itself will be approximately the diameter of a pencil to the size of your index finger.
The andrenid bees are solitary, which means each female does her own work to provision a nest cell with nectar and pollen as a food for her offspring. Several females may cooperate to use a common entrance tunnel and corridor. The bees themselves are 1/4 to 1/2 inch long and variable in color (mostly dark, but some with markings of white, yellow or reddish brown).
"Mining bees" are not a serious pest. The entrances to the tunnels are disruptive to the lawn but not usually damaging. It appears the grass is thin because of the bees, but it is more likely the bees are in the area because the grass was already thin.
The threat of being stung by these insects is usually highly overrated. The bees are docile and not likely to sting unless handled or threatened. Control is usually not necessary unless the bees are nesting close to human activity.
The following control alternatives come to mind: 1) do nothing (these pollinators are beneficial insects, after all); 2) level the area and establish a thick turf or ground cover tolerant to the site (shade-adapted, for example); 3) treat individual nest openings with Sevin dust; or 4) spray the infested area with a turfgrass insecticide to discourage the bees. I'm not convinced the insecticides are justified for these interesting little bees but some people do describe a significant problem that they feel needs response.
This article originally appeared in the May 24, 1996 issue, p. 86.