I wondered about this unusually perforated woodpile, located on the long porch of the building where I’m staying at Andrews Experimental Forest — until I met the phenology researcher who set them up. He explained that mason bees take advantage of existing holes drilled in trees to deposit their eggs in chambers, each walled from the next with a curtain of mud, and each provisioned with a supply of pollen. Look closely: you’ll see empty holes, partially-plastered holes, and finished holes that have been sealed shut with a protective daub of masonry. Some of the mudded holes were still visibly fresh, a darker tone of clay than the dried holes.
The mason bees were busy today (they love sunny days, according to the researcher).