An Introduction to Cavity-Nesting Bees in the Puget Sound Region

An Introduction to Cavity-Nesting Bees in the Puget Sound Region

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Elias Bloom, Ph.D Student, Department of Entomology, Washington State University, Rachel Olsson, Ph.D. Student, Department of Entomology, Washington State University, Emily Wine, M.S. Student, Department of Entomology, Washington State University, Robert Schaeffer, Postdoctoral Research Fellow, Department of Entomology, Washington State University, David Crowder, Assistant Professor, Department of Entomology, Washington State University
Learn to harness a variety of wild bees in your backyard using these simple and effective methods.
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Cavity-nesting bees are important pollinators, contributing billions of dollars in global pollination services each year. Adequate nesting resources across agricultural and natural landscapes are essential for the survival and reproductive success of these pollinators, and the pollination services they provide on farms. In the Puget Sound Region of Washington state, cavity-nesting bees are likely significant contributors to pollination services. However, compared to other parts of the United States, relatively little is known about cavity-nesting bee diversity in the Puget Sound Region, or techniques that could be used to conserve them. Here, we provide profiles of the major groups of cavity-nesting bees found in the Puget Sound Region and examples of artificial and natural nest resources for these species. We also provide information on how citizen science can enhance our understanding of cavity-nesting bees through monitoring, thereby contributing to the conservation of these pollinators throughout the Puget Sound Region.


Wild bees are important pollinators that provide billions of dollars a year in global pollination services (Goulson et al. 2015). However, many wild bee species are threatened by habitat loss due to agricultural intensification and urbanization (Mader et al. 2010; Goulson et al. 2015). In turn, research has shown that providing suitable nesting resources on, and around, farms can boost wild bee abundance and related pollination services to crops (Potts et al. 2005; Winfree et al. 2011). However, the diversity of cavity-nesting bees, and nesting requirements associated with each species, remain poorly understood in the Puget Sound Region of Washington state (Cane et al. 2007). This guide summarizes cavity-nesting bee biology (Section I), identification (Section II), nesting habitat (Section III), and conservation through citizen science (Section IV). We do not cover floral resources for bees, or details on ground-nesting bees. However, websites with such content can be found in the Useful Internet Links section of this guide. The objectives of this guide are to increase bee conservation and literacy in the Puget Sound Region.

Cavity-Nesting Bee Biology

Approximately 30% of bee species build aboveground nests in hollow or pithy stems, and tunnels left in wood by herbivores (Cane et al. 2007). Beginning in spring, adult bees emerge and build nests that are divided into individual brood cells, each provisioned with an egg. Adult bees collect pollen and nectar to provision nests, and when eggs hatch the larvae feed on these resources before pupating. These cells are sealed with materials such as leaf tissue, mud, resin, or rocks, shown in Figure 1 (Cane et al. 2007). Adult cavity-nesting bees are solitary and usually do not care for their offspring beyond supplying pollen and nectar. Emergence continues throughout the summer season and tapers off in the fall, depending on the bee species. This season-long emergence may help promote pollination over a long period of time.

Figure 1. An x-ray image of a cavity-nesting bee tunnel divided into individual brood cells with developing larvae and sealed with leaf tissue.

Cavity-Nesting Bees of the Puget Sound Region

To date we have identified five major groups of cavity-nesting bees on farms in the Puget Sound Region. Many of these bees are known to be important pollinators. The groups listed here are considered to be the dominant groups found on farms, but do not account for all cavity-nesting bee species. Many of these groups possess key morphological characteristics and utilize specific nesting materials (Table 1).

In this section, we profile each of these groups to aid in identification by farmers and gardeners. In Section III we provide further details on creating habitat for cavity-nesting bees.



Copyright Washington State University

Published January, 2018

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