In some areas, especially with lots of trees, woodpeckers can be a problem, particularly in winter when food is scarce.
It seems that only the Green Woodpeckers are the culprits.
Once one discovers what a valuable food source your hives are, they drill holes through into the brood box in the search for bees to eat.
Consequently, those bees not providing lunch for the woodpecker are killed by the weather and other predators due to the large holes in the sides of the hive.
Covering the hives with wire or nylon netting is the usual preventative method. Hanging strips of plastic or cloth loosely down the sides of the hive from the top also works well.