Sapsuckers drill holes in trees so that they can feed on the sap and on the insects that the sap attracts. Insects are captured in the sticky sap flows. These woodpeckers often create horizontal rows of holes that they continue to use throughout the season. As the holes heal over in order to prevent water loss and infection in the tree, sapsuckers create new rows of holes. Collectively, these holes are known as sap wells*.
“Over 30 species of birds have been documented feeding from sapsucker wells, as well as numerous mammals. Yellow-bellied sapsuckers and ruby-throated hummingbirds have an interesting relationship. When hummingbirds arrive north in the spring, they follow sapsuckers around and depend on their wells for nourishment until flowers begin to bloom”. (Bird Tracks and Sign*, page 256)
*Elbroch, M. & Marks, E. 2001, Bird Tracks and Sign, Stackpole Books, Mechanicsburg, PA.