Soil sanctuaries: Experimental manipulations enhance ground-nesting bee habitat

A. Fredenburg, K. Goodell. 2026. Ecosphere 17(10): e70781. DOI: 10.1002/ecs2.70781

Abstract

As the evidence of pollinator declines mounts, effective habitat enhancement and management strategies are urgently needed. Current methods focus on improving floral resources, overlooking nesting habitats, especially for ground-nesting bees. Ground-nesting bee habitats remain poorly understood, and the lack of evidence-based methods to provide nesting habitats presents a significant challenge. To determine whether soil manipulations attract nesting bees and which environmental conditions are associated with nesting preference, we constructed experimental plots at 21 sites along an urban gradient in Columbus, Ohio, and implemented four soil surface treatments, which we compared with unmanipulated controls: bare ground, leaf litter, mounded soil, and pebbles. We collected nesting individuals through hand netting during nest observations and emergence traps, assessing soil surface substrate preferences and associations with soil conditions, while controlling for local habitat availability. Manipulated treatments attracted significantly more nesting females than controls, and bees in the genus Halictus were specifically attracted to bare ground treatments. Treatments differed in soil temperature, moisture, and compaction, with no one condition emerging as a significant driver of nest site attraction, suggesting ground-nesting species can nest in a range of soil conditions. Treatment plots attracted more nesting bees at sites with steeper slopes, less bare ground availability, and more abundant ground-nesting bee populations, indicating that site-level features influence attraction to our manipulations. Our findings demonstrate that simple soil surface manipulations, such as patches of bare soil, leaf litter, pebbles, or mounded soil, effectively attract ground-nesting bees to nest. Including such manipulations, or “soil sanctuaries,” alongside a pollinator garden in residential or park settings offers dedicated spaces for bees to nest and could enhance the local conditions for bees by completing the habitat requirements for ground-nesting species, especially in locations where preferred nesting substrates are limited.