The holes were likely created by sapsuckers. Members of the woodpecker family, sapsuckers damage trees by drilling holes in the trunk or large branches. Sapsucker damage is very distinctive. They drill uniform, 1/4 inch holes in distinct rows (in contrast, the holes created by insects are random). Sap that flows from these wounds is eaten by the sapsuckers. They also feed on insects, such as ants, beetles and wasps that are attracted to the sap. Trees most commonly attacked by sapsuckers include apple, crabapple, sugar maple, mountain ash, birch and pine.

Sapsuckers live during the summer in the northern United States and southern Canada, migrating south through Iowa between mid-September and mid-October.  They overwinter in the southern United States, migrating back north between late March and mid-May.  These are the only times that trees are damaged in Iowa.

The damage caused by sapsuckers is usually not serious. However, sapsuckers can destroy trees if they drill several rows of holes around the trunk within a small area. The bands of holes effectively girdle the tree trunk. To discourage additional damage to trees, home gardeners can wrap a piece of burlap around the damaged areas. Another option would be to spread a sticky substance, such as Tanglefoot, around the affected area.