Solitary Ground Bees Not a Threat
This time each year many homeowners notice small dirt mounds in their yard, at parks, or recreational fields created by small bees. In many cases, these are mistaken for ant hills or mounds made by large wasps like cicada killers. In fact, they are made by solitary, ground-nesting bees in the family Andrenidae.
These are among our earliest native pollinators to emerge so they can take advantage of early blooming flowers like maples and red buds. N.C. Cooperative Extension offices occasionally receive calls from worried or frustrated homeowners who are concerned about their safety or the condition of their lawn. Homeowners should not be worried because these bees are non-aggressive and leave after a few weeks.
A single female bee builds the nest by burrowing into the ground. She prepares multiple larval cells within the nest where eggs are laid. She provisions larval brood with a mixture of pollen and nectar before closing the nest entrance and starting another. The female dies shortly thereafter, leaving the next generation safely tucked away in the ground. The visual spectacle of these bees is due largely to males seeking newly emerged females as well as the small mounds of soil beside each nest.
Solitary bees prefer to nest in dry, sparsely vegetated areas, and are simply taking advantage of desirable soil conditions. Aside from pollination, they are also providing a valuable service aerating your lawn. Measures that will make sites less appealing are to improve the density of the lawn or to irrigate over 3-4 weeks while bees are active. Native bees are an important part of ecosystems and food production. Consider steps to protect these bees or at least use non-lethal means to encourage them to nest elsewhere.