Monday, March 18, 2013

Ground Nesting Bees

I just received an email from Mike Waldvogel, NC Extension Specialist, Structural & Industrial Pests. Since I do receive calls every year concerning these bees I thought I would get the word out in advance. If you still have questions, please feel free to call.

In the near future, you may start seeing either small mounds of soil in your yard or "swarms" of bees showing up in the landscape. Schools and child care facility managers often panic because they think these are swarms that ose a health risk to the children. They are most likely the solitary bees such as the "colletids" and "andrenids" that often emerge at this time of year. Even with the cooler weather we've experienced, rain that has softened the soil and open exposed areas warm more quickly contributing to this burst of activity. 
The bees begin foraging for food and seeking out new nesting sites. This activity will continue for about the next tow months depending on  the area of the state and the species of bee. They dig vertical tunnels in the soil on which they make small side chambers that they store pollen for their offspring. These bees are "solitary" which means there is not a true colony. A lot of the "swarming" that you see are male and female bees. (Think of your lawn as a big singles bar for bees). These 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 they are all made by individual queens which do 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 similar species, that will likely attach them if they venture to 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 are trying to protect a nest. There is no "mass attack" as might occasionally occur with a close encounter of the yellowjacket kind!
These bees are beneficial and should be left alone if possible. If you want something done, you can apply almost anything that you would tyically use outdoors for perimeter treatments. One problem is that the bees often try to dig into the sand in play ares at schools, childcare facilities, etc. Of course parents and teachers are concerned about stinging incidents particularly if a child 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.
If the bees try to next 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 of soapy water which will bring the bees out. Since sopa will work as an insecticide to some extent, it will kill some of the bees in the process but I still consider this preferable over the use of conventional insecticides. The waterlogged soils will hopefully deter the bees but again we're looking at activity that can take place over several weeks. 

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