Holes in trees offer clues about a tree’s health and its environment. These openings result from various natural causes, including insects, birds, fungi, and weather phenomena. Understanding their origin provides insight into the tree’s condition and the natural processes occurring within its ecosystem. While some holes are cosmetic, others signal underlying issues that warrant closer inspection.
Holes Made by Insects
Insects create holes in trees as part of their feeding or reproductive cycles. Wood borers, primarily larval beetles, moths, or wasps, tunnel into the wood or beneath the bark. These tunnels disrupt the tree’s ability to transport water and nutrients, potentially weakening the tree over time. The appearance of holes varies by insect; for instance, emerald ash borers create distinctive D-shaped exit holes, approximately 1/8 inch wide, on ash trees.
Other borers often leave round or oval exit holes with jagged edges, producing coarse, sawdust-like material known as frass. This frass may be visible around the tree’s base or extruding from the holes. Carpenter ants, unlike borers, do not consume wood but excavate tunnels within decaying or moisture-damaged timber to build nests. Their activity results in smooth, hollowed-out galleries, and they often push out fine sawdust-like frass that can contain insect parts. The presence of these holes and frass indicates an active insect infestation.
Holes Made by Birds
Birds, especially woodpeckers and sapsuckers, create tree holes with distinct patterns. Sapsuckers drill neat rows or columns of small, shallow holes, about 0.25 inches in diameter. These birds feed on tree sap that oozes from these “sap wells” and consume insects attracted to the sap. The systematic arrangement of sapsucker holes makes them easy to identify.
Other woodpecker species create larger, irregular or oval-shaped holes with ragged edges, sometimes extending deep into the tree. These excavations are made while foraging for insects like wood-boring beetles or ants. Woodpeckers may also create larger cavities for nesting. While sapsucker damage is orderly, other woodpecker holes are more random and varied in size, reflecting their search for prey or nesting sites.
Holes from Fungi and Other Factors
Fungi and environmental factors also create holes or openings in trees. Fungal infections, such as wood rot or cankers, result in decayed or hollowed-out areas. Cankers are localized areas of dead tissue that appear as sunken, discolored, or cracked lesions on the bark, sometimes leading to bark loss and exposing the inner wood. As fungi break down wood, they create interior cavities, often called “heart rot.”
Environmental stressors also contribute to tree holes. Frost cracks are vertical splits in the tree trunk that occur when temperatures fluctuate rapidly, causing wood to expand and contract unevenly. These cracks may reopen in subsequent winters, serving as entry points for pathogens and leading to decay. Less common causes include lightning strikes or physical injuries, which create initial wounds allowing decay to set in and form larger openings.
Interpreting Tree Marks
Identifying the cause of tree holes involves observing several visual cues. The hole’s shape is a primary indicator: small, round holes suggest bark beetles, while D-shaped holes indicate emerald ash borer activity. Oval or irregular holes point to other wood borers or woodpecker foraging. The hole’s size also provides clues, with smaller holes indicating insect emergence and larger ones suggesting woodpecker activity or advanced decay.
The pattern of holes is equally informative. Neat rows or grids of shallow holes indicate sapsucker feeding. Randomly distributed holes, sometimes with sawdust-like frass, signal a borer infestation. The presence and type of frass, sap flow, or discolored bark around holes also offer diagnostic insights. Wet spots or dark stains can accompany flatheaded borer activity. Observing these details provides a comprehensive understanding of what might be affecting a tree.