I've had several recent requests for detailed information on our native leafcutter bees and how to best encourage their presence in the Desert Garden. I made some inquiries and received the following note from bee expert Stephen Buchmann:
Thanks for your questions. Its refreshing, as a native bee biologist, to hear someone asking about how to appreciate and raise native leafcutter bees, instead of complaining about their largely minor cosmetic damage to ornamental plants. :-)
You can use the Blue Orchard Bee nests, 3-5 inch deep holes fitted with paper (not plastic) straws, or just naked holes [drilled into untreated wood blocks]. The optimal hole diameter is 7 - 8 mm. Space the holes in a regular grid on 1/2 inch or 1 inch centers. Make sure the holes are blind-ended tunnels that don't come out the back of the block of wood.
The time to place theses nests is NOW, during the Palo Verde and Ironwood bloom (some of their preferred plants). They also like mesquite.
I have had about 12 of these nests on my back patio for the past 9 years. They routinely attract females of Megachile (the subgenus Chalicodoma, which used to be its own genus). These are large slender black and white-striped handsome bees with massive jaws. You will typically get 4 or 5 similar looking species. The end plug capping gives them away. Some species use masticated leaves, others use resin and sand and some form very messy looking debris end plugs with odd bits of bark, leaves etc. Enjoy! These pollinator pets make great watchable wildlife.
Hang the wood block nests up high. At least shoulder height to about 8 feet up under an overhang so they don't get direct sun or rain. Face them south or SE. The nests will overwinter just fine. Sometimes you get a few native cuckoo bees, the parasitic genus Stelis. After a few years, you may want to put up freshly drilled nests near the old ones.
Please visit www.pollinator.org for more information on native pollinators across the country.
Stephen Buchmann is an Associate Professor with the University of Arizona Department of Entomology, founder of The Bee Works, and author of several books on bees and pollinators, including The Forgotten Pollinators, Letters from the Hive, and Pollinators of the Sonoran Desert; a Field Guide, all available through Amazon.com.