"scientists recently discovered a rare, solitary type of bee that makes tiny nests by plastering together flower petals"

From 2010:

She then shapes the multi-colored petals into a cocoon-like structure, laying one petal on top of the other and occasionally using some nectar as glue. When the outer petal casing is complete, she reinforces the inside with a paper-thin layer of mud, and then another layer of petals, so both the outside and inside are wallpapered -- a potpourri of purple, pink and yellow.

These meticulous shells are just over a half-inch long and usually will house just one tiny egg.