Holes in a trunk or bark: what the sources say it may indicate

This page reports what the official source says. It is not legal advice: ask the office named here. It does not say what made the holes in any tree, whether the tree is healthy or what should be done about it. The sources sort holes by size and layout. Only the UConn article sends a reader to anyone, and only for Asian longhorned beetle, to the plant diagnostic lab of the state.

What UConn Extension describes

The UConn Extension article Got Holes in Your Trees?, by an assistant extension educator, names wood-boring insects and birds as the common causes of holes in bark. It says that with insects the larvae feed inside the tree, while the adult beetles or moths usually make the holes, either as entry holes where they go in to lay eggs or as exit holes where they come out.

Hole as the article describes it	What the article links it to
Tiny round entry holes, many together like shot holes	Bark beetles, which are a few millimeters long. The article says they are often drawn to trees stressed or weakened by drought, other pests or disease.
D-shaped or oval exit holes	Metallic wood-boring beetles. The article gives the emerald ash borer exit hole as D-shaped and 4 to 5 millimeters across.
Round exit holes larger than bark beetle holes	Round-headed or longhorned beetles. The article says Asian longhorned beetle holes are deeper than those of many similar beetles and sends a person who is concerned to the plant diagnostic lab of the state.
Large, irregular, rough-edged holes	Woodpeckers pecking toward insects, including borers, under the bark.
Small, uniform, round holes in rows or grids	Sapsuckers, which the article says feed on tree sap, not insects.

What Purdue Extension describes

The Purdue Extension Whitley County article Something is Making Holes in My Tree, dated April 25, 2025, says the presence of holes usually means an insect or woodpecker has taken an interest in the tree and the tree may be in a state of decline. It lists size, number and arrangement as the clues: holes run from very small to up to 3/8 inch, random small holes point to an insect, random ragged holes to a woodpecker after insects, and holes in a straight line to sapsuckers. It quotes Purdue writers who say sapsucker damage that is limited and minor usually leaves the tree recovering, while repeat injury in one place can open the tree to insects or decay fungi and, over time, girdle a branch or trunk. It notes that woodpeckers are protected by the Migratory Bird Treaty Act in the United States.

What Iowa State Extension describes

The Iowa State Extension Yard and Garden answer Are bands of holes in my pine tree a sign of borers?, last updated August 29, 2024, says sapsucker holes are uniform, 1/4 inch and in distinct rows, while insect holes are random. It says sapsucker damage is usually not serious, but several rows of holes around the trunk in a small area can girdle it. It names apple, crabapple, sugar maple, mountain ash, birch and pine as the trees most often attacked.

Where the sources agree

All three sources use the arrangement of the holes as a clue: rows suggest sapsuckers, and Purdue and Iowa State say random holes suggest insects. UConn says bark beetles are often drawn to stressed or weakened trees, and Purdue says holes may mean a tree is in decline. The guides on woodpecker damage, emerald ash borer and whether a tree is dying report more.

Who to call

ISA Find an Arborist: the ISA directory for an arborist who can examine a tree
Consulting arborists by country: the credentials and registers consulting arborists hold in each country
UConn Plant and Soil Health Center: the University of Connecticut plant diagnostic lab; the UConn article sends a suspected Asian longhorned beetle to the state plant diagnostic lab, and other states have their own