Build it and they will come

by John M. Row, Assistant Manager
Manhattan Plant Materials Center

Interest in managing for native bees has been emphasized in recent years with the decline of the European honeybee and loss of habitat that supports native bees. According to the Xerces Society, “about 30% of the 4,000 species of bees native to North America nest in small tunnels such as hollow plant stems, abandoned borer-beetle holes in snags, and similar locations.” One way to help native bees is to provide artificial nesting sites where they can raise their young. Crops located in the vicinity benefit from the increased numbers of pollinating native bees.

An artificial bee nest was built of thin wall polyvinyl chloride (PVC) pipe with one end capped-off, filled with reed grass stems approximately 6.5″ long, as one option for providing a nest site. The reed was cut so that a single node was left at one end of each stem. An awl was used to clear any inner stem connective tissue in each reed so that the stems were essentially hollow. This left about 6 inches of hollow reed in which female bees could lay their eggs. The reeds were inserted into the pipe with the node end toward the capped-off end (back) of the pipe. Not all solitary bee species have the same cavity size requirements for nesting. The beauty of using something like reed is that the openings (cavities) are variable in size and will be attractive to more than one species of bee. The pipe filled with reed was hung under the eave of a house 7′ 5″ above ground facing northeast. In 2011, only 17% of the openings appeared to be occupied. Occupancy or use of a cavity is often difficult to determine due to the inability to see down into the cavity. In the spring of 2012, things really started happening.

I did not know what to expect, but I imagined a single solitary bee showing up and going into an opening and then leaving. What would be the chance of ever catching one in the act? What I observed on several afternoons was what might be described as a “beehive of activity” at the nest site. Not a single bee, but several bees of different species busily entering and leaving the reeds and returning again and again laying eggs and partitioning off cells. By early April, approximately 28% of the openings had seen bee activity and 16% had been filled to the end of the reed. At least 2% had experienced emergence from previously filled cells. By late summer, 99% of the reeds had been used over the 2-year period. Most of the reeds were completely filled, or nearly so, and capped off or sealed with soil or plant material, 36% and 64%, respectively. A variety of plant materials was used with various shades of green, pink (possibly from rose petals), yellow (flower petals or resin), or salmon in color.

During the summer, bees of various sizes were observed visiting the bee nest.
Artificial nests can also be made of blocks of wood with holes of various diameters drilled into them. The holes must be very smooth for the bees to accept them as nesting cavities. Ideally, the holes are drilled large enough that they can be lined with paper straws. This makes the nest blocks easier to maintain. The downside is that the single diameter opening may limit the nest block to a few species of bees. The straws can be removed making it easier to clean the nest block without disturbing larvae that have yet to emerge.

For more information on artificial nests for native bees, refer to Invertebrate Conservation Fact Sheet: Tunnel Nests for Native Bees at www.xerces.org