Woodpecker damage varies widely, ranging from small pinprick holes to large, excavated cavities. The appearance depends entirely on the bird’s species and purpose, indicating whether it was foraging for insects, harvesting tree sap, establishing territory, or constructing a nest. Identifying the specific visual characteristics of these markings helps determine the activity occurring on a tree or wooden structure.
Small Holes Made for Insect Foraging
The most common form of damage is the small, shallow hole made while hunting for insects and larvae beneath the bark. These foraging holes, typically created by species like the Downy or Hairy Woodpecker, are often small, circular, and roughly the size of a pencil eraser or dime. The birds use their sharp bills to probe and chip away the outer wood layers to access prey.
These small holes are generally scattered randomly across a tree trunk or wooden siding, giving the surface a peppered appearance. Woodpeckers listen for insect movement, resulting in exploratory rather than systematic impact marks. The depth of these holes is usually minimal, just enough to expose the insect or its tunnel, contrasting with deeper excavations made for other purposes.
Smaller woodpecker species, like the Downy, often target dead limbs, smaller branches, or large plant stems where insects are easier to reach. Their less powerful bills create smaller, clean, shallow punctures. Larger insect-foraging species may produce slightly wider or more ragged holes as they tear away bark to access galleries of ants or beetles.
Defining Patterns of Sap Wells
A distinctly different pattern of damage is produced by sapsuckers, a specialized group of woodpeckers that feed on tree sap and the insects trapped within it. These birds create highly organized sap wells that appear as precise, geometric patterns on the bark of living trees. The holes are shallow, numerous, and arranged in straight horizontal or vertical lines, sometimes forming a grid.
Sapsuckers initially drill small, round holes that penetrate the wood to access the upward-flowing xylem sap, which is most active in early spring. They later drill shallow, rectangular holes that tap the phloem layer, which carries sugar-rich sap from the leaves. This systematic approach ensures a continuous flow of sap, which the bird laps up with its specialized brush-tipped tongue.
The tree often exhibits weeping or staining around these feeding sites as the sap flows and oxidizes, sometimes attracting insects, hummingbirds, and small mammals. The organized, uniform rows of these wells are unique to sapsuckers and are the clearest indicator of their presence. These patterns are usually found on trees with sweet sap, such as birch, maple, and fruit trees.
Large Excavated Holes for Nesting and Roosting
Woodpeckers create large, deep cavities that serve as shelter for roosting or as nests for raising young, often in dead trees or dead sections of living trees. These structural excavations are significantly larger than foraging holes, with the entrance size varying by species. A larger species, like the Pileated Woodpecker, creates an entrance that can be three to four inches or more across.
The shape of a nesting hole entrance is typically circular or slightly oval, sometimes appearing tear-drop shaped, and has smooth, clean edges. The excavation extends deep into the heartwood, forming a chamber over a foot deep to accommodate the bird and its clutch. Wood chips, known as frass, are a sign of recent excavation, often accumulating in a visible pile at the base of the tree.
These larger holes provide roosting sites for protection from weather and predators during the non-breeding season. Unlike foraging marks, which may appear anywhere, nest and roost holes are generally located high up on the main trunk. Because of the effort required, a new hole is usually excavated each year for nesting, though old cavities are often repurposed for roosting.
How to Differentiate Woodpecker Damage from Insect Infestation
Distinguishing between damage caused by a woodpecker and the exit holes created by wood-boring insects requires close attention to the hole’s characteristics. Insect exit holes are typically small, uniform in size, and perfectly symmetrical, reflecting the shape of the insect that bored its way out. For instance, the Emerald Ash Borer leaves a distinct, small D-shaped exit hole, while other beetles produce round holes.
Woodpecker foraging holes, in contrast, are usually messier, with slightly ragged edges and irregular shapes, due to the forceful chipping motion of the bird’s bill. If the damage consists of numerous tiny holes without wood dust, it may indicate a bark beetle infestation. Boring insects may also leave behind fine, flour-like sawdust, or frass, which is often packed into the tunnel or pushed out in small piles.
Damage from fungal decay presents differently, typically appearing as soft, crumbling wood or areas where the bark has sloughed off naturally. If the wood is soft and breaks away easily, exposing an irregular pattern of decay, it is not a clean, chiseled woodpecker hole. Woodpeckers are often attracted to trees already infested with insects or suffering from decay because the wood is softer and prey presence is higher.