How to build nest boxes for solitary bees and wasps
References
Budrys, J. et al. Bioindication using trap-nesting bees and wasps
Heard, T. Suggested designs for trap-nesting solitary bees
Hallett, P. 2001. A method for 'hiving' solitary bees and wasps American Bee Journal
http://resonatingbodies.wordpress.com/gardens-youth/pink-bee-condo/