Ground Nesting Bees, by Mike Waldvogel

For those of you who answer pest questions:

You may start getting calls soon from people seeing either small mounds of soil in their yards or reporting "swarms" of bees. Schools and child care facility managers often panic because they think these are swarms that pose a health risk to the children. However, they are most likely the solitary bees such as the "colletids" and "andrenids" that often emerge this time of year.

The bees begin foraging for food and seeking out new nesting sites. This activity will continue for about the next two months, depending on the area of the state and the species of bees. They dig vertical
tunnels in the soil on which they make small side chambers where they provision pollen for their offspring. These bees are "solitary," which means there is no true colony. A lot of the "swarming" that
you see are males and females attempting to pair up and mate (tell people to think of their lawn as a big singles bar for bees). The bees frequently make small mounds in the soil, often where the soil is loose and vegetation may be sparse. You frequently see clusters of these nests, but each nest is made by an individual queen which does the work without the help of workers as occurs in a honey bee nest.

Although the damage can be unsightly with large numbers of mounds in the yard, it is mostly a cosmetic issue. The bigger problem is usually that people walking by panic because they assume that these are swarms of honey bees (or a similar bee) that will likely attack them if they venture too close to "the nest." Turf-nesting bees can sting but rarely do so, since they are not "social" and you don't have a large number of worker bees that trying to protect a nest. There is no "mass attack" as might occasionally occur with a close encounter of the yellowjacket kind (and it's still early in the year
for us to see any yellowjacket colonies out there).

These solitary bees are beneficial and should be left alone if possible. If customers want something done, you can apply almost anything that you typically use outdoors for perimeter treatments. One problem is that the bees often try to dig into the sand in play areas at schools, childcare facilities, etc. Of course, parents and teachers are concerned about stinging incidents, particularly if a child (or teacher) is hypersensitive to bee stings. In those instances, I still strongly discourage any chemical treatment, particularly in sandy play areas where kids come into direct contact with the soil (and which they might get in their mouths as well). However, facility managers have to weigh the safety of children (and staff) and the misinterpretation by the public of ignoring the problem as meaning they lack concern about the children.

If the bees try to nest in a sandbox, a simple solution is to cover it during the day but it will take a few weeks for you to deter most of the bees that show up over time. While the tarping approach isn't always successful, wider areas can be saturated with plain or soapy water which will bring the bees out. Since soap will work as an insecticide to some extent, it may kill some of the bees in the process but I still consider this preferable over the use of conventional insecticides IF people are unwilling to simply ignore the problem. The water-logged soils will hopefully deter the bees but again we're looking at activity that can take place over a few weeks.

Information, including pictures, of these bees and the "damage" that they cause can be found at:

http://www.ces.ncsu.edu/Insects/O&T/lawn/note100/note100.html