Holes in Tree Bark: Woodpeckers, Borers, or Bees?

Holes in tree bark are most often made by woodpeckers (either neat rows of shallow sap wells or scattered pits where they hunt insects), wood-boring beetles that leave round exit holes with sawdust-like frass, or carpenter bees drilling bare limbs. The pattern, the hole size, and whether you see frass or oozing sap tell you which one — and whether the tree is truly in trouble.

A yellow-bellied sapsucker clinging to a tree trunk
The yellow-bellied sapsucker drills neat rows of shallow holes in bark to feed on sap. Photo: Rhododendrites, CC BY-SA 4.0

Most likely causes

  • Yellow-bellied sapsucker — neat horizontal rows of shallow, evenly spaced holes
  • Insect-hunting woodpeckers — scattered larger holes chipped into the wood
  • Wood-boring beetles (borers) — round 1/8–3/8 inch exit holes with frass
  • Carpenter bees — perfectly round 1/2 inch holes in bare limbs with sawdust
  • Bark beetles — many tiny shot-holes, often oozing on a stressed tree

Not quite what you're seeing? Answer four quick questions and the clue finder will point you to a closer match.

Compare the possible causes

Possible cause Key signs When it happens How likely
Yellow-bellied sapsucker wells Neat horizontal (and sometimes vertical) rows of shallow, evenly spaced holes that weep sap Spring and summer, repeated on the same favored trees year after year Common
Woodpeckers hunting insects Scattered, irregular holes chipped deeper into the wood, often with bark flaked off around them Year-round, but noticeable in fall and winter when birds forage for overwintering larvae Common
Wood-boring beetles (borers) Round or D-shaped exit holes about 1/8–3/8 inch across, with sawdust-like frass in bark crevices or at the base Adults emerge late spring through summer; damage builds over one or more seasons Common
Carpenter bees A single perfectly round hole about 1/2 inch wide in bare, unpainted wood, with coarse sawdust below it Spring into early summer, when females excavate nesting galleries Less common
Bark beetles Many tiny shot-hole-sized punctures, sometimes with pinhead beads of oozing sap or fine reddish dust Warm months, especially on drought-stressed or declining trees Less common

Visual clues to check

  • Read the pattern first: neat straight rows point to a sapsucker; random pits mean insect hunting; a lone clean hole means a carpenter bee
  • Measure the hole: 1/8–3/8 inch round or D-shaped suggests borers; a crisp 1/2 inch circle suggests carpenter bees; tiny shot-holes suggest bark beetles
  • Look for frass or sawdust: fine sawdust-like frass in bark cracks or at the base points to borers; coarse sawdust below a hole points to carpenter bees
  • Check for oozing sap or beads of pitch, which can mean sapsucker wells or a tree defending against bark beetles
  • Note the tree species: D-shaped exit holes on an ash tree are a serious warning sign for emerald ash borer
  • Scan the whole canopy for thinning or dead branches above the holes, which suggests something is damaging the tree, not just its bark

The causes in detail

Yellow-bellied sapsucker wells

Despite the name, the yellow-bellied sapsucker is a woodpecker that drills orderly rows of small holes, called sap wells, to feed on the sap and the insects it attracts. The tidy, repeating pattern is the giveaway — no other cause makes such straight lines. It's usually cosmetic on an otherwise healthy tree, though a heavily ringed young trunk is worth watching.

Woodpeckers hunting insects

When a woodpecker digs random, ragged holes rather than neat rows, it is usually chasing insects living inside the wood. In that case the bird is a symptom, not the problem: it often signals a borer or beetle infestation under the bark. Treating the woodpecker is pointless — the real question is what it is eating.

Wood-boring beetles (borers)

Borers spend most of their life as larvae tunneling under the bark, then chew their way out, leaving small round exit holes and pushing out frass (a mix of sawdust and droppings). On ash trees, D-shaped exit holes are a red flag for emerald ash borer, a highly destructive pest. Borers most often attack trees already stressed by drought, injury, or disease.

Carpenter bees

Carpenter bees bore clean, near-perfect half-inch holes into bare limbs, dead branches, and untreated wood, then tunnel sideways to nest. You'll often see a pile of coarse sawdust beneath the entrance and a large bee hovering nearby. In living trees they usually favor dead or exposed wood, so the damage is typically minor — see round-holes-in-wood-with-sawdust for the same holes in structures and fences.

Bark beetles

Bark beetles are small and attack in numbers, riddling the trunk with pinhole-size entries. Healthy trees often 'pitch out' the invaders, leaving little beads of sap, but stressed or dying trees can be overwhelmed. Widespread shot-holes on a thinning, discolored tree usually mean the tree was already in decline.

When to worry

  • D-shaped exit holes combined with canopy thinning or dieback, especially on ash — a possible emerald ash borer sign; contact a certified arborist
  • Rapid decline: leaves yellowing, branches dying back, or bark splitting over a single season
  • Woodpeckers working the same trunk intensely, which often means an active insect infestation underneath
  • Many holes ringing a young or newly planted trunk, which can girdle and weaken it
  • Sawdust, frass, or sap flow that increases week over week rather than staying stable

What to do now

  1. Identify the pattern and hole size before acting — rows, random pits, one clean hole, or many shot-holes each point to a different cause
  2. Keep the tree healthy: water deeply during drought, mulch properly (not against the trunk), and avoid wounding the bark, since stressed trees attract borers
  3. Photograph the holes with something for scale and note the tree species so you can compare against borer and beetle guides
  4. For any borer signs, D-shaped holes, or a large or valuable tree, get an assessment from an ISA-certified arborist
  5. Leave sapsucker wells alone on a healthy tree; if you want to protect a favored young trunk, loosely wrap burlap during peak spring activity

What not to do

  • Don't move firewood from an affected tree to another property — this is how borers like emerald ash borer spread to new areas
  • Don't fill borer holes with putty or spray a random insecticide before the pest is identified; timing and product depend entirely on the species
  • Don't try to kill the woodpecker or seal it out with tar or sticky repellents — it is a clue to an insect problem, and harming it is illegal for native species
  • Don't carve, gouge, or paint over the holes to 'clean them up,' which only wounds the tree further

Frequently asked questions

Are woodpecker holes in my tree bad for the tree?

Neat rows of shallow sapsucker holes are usually cosmetic on a healthy tree. Scattered, deeper holes are more concerning — not because of the bird, but because they often mean the woodpecker is digging out insects living in the wood. In that case the underlying borer or beetle problem is what matters.

How can I tell borer holes from carpenter bee holes?

Borer exit holes are small, roughly 1/8 to 3/8 inch, often round or D-shaped, and come with fine sawdust-like frass. Carpenter bee holes are larger and strikingly round — about a half inch — with coarse sawdust below and often a big bee nearby. The size and the type of debris are the quickest tells.

What do D-shaped holes in ash tree bark mean?

D-shaped exit holes on an ash tree are a classic sign of emerald ash borer, one of the most destructive tree pests in North America. Paired with canopy dieback or bark splitting, they warrant a call to a certified arborist or your extension office right away, and you should never move the wood.

Should I fill the holes in my tree bark?

No. Filling or sealing holes traps moisture and can worsen decay without stopping the cause. Focus on identifying what made the holes and keeping the tree vigorous; a healthy tree compartmentalizes minor wounds on its own.

Related yard clues

Plant Damage Bark Stripped From Trees: Squirrels, Deer, Voles, or Birds? The height of the damage tells you the most: bark gnawed at ground level is usually voles or rabbits, shredded bark from 1 to 4 feet up is deer rubbing their antlers, and stripped patches on upper branches point to squirrels. Neat horizontal rows of shallow holes are a sapsucker's work — and any damage that circles the whole trunk (girdling) puts the tree at real risk. Read the guide → Plant Damage Why Is My Tree Dripping Sap? Sticky Ooze Explained A tree dripping sticky liquid is often not leaking true sap at all — it's usually honeydew, the sugary waste of aphids, scale, or lanternflies feeding in the branches above. Real sap does flow from pruning cuts and storm cracks, and darker, foul-smelling ooze can be bacterial slime flux. Checking the leaves above the drip and the smell of the ooze usually points to the cause. Read the guide → Plant Damage White Spots on Tree Bark: Lichen, Bugs, or Mildew? White or grayish patches on tree bark are most often lichen — a harmless organism that simply perches on the bark and is not a disease or parasite. The other common causes are cottony white scale or woolly aphids, powdery mildew on green bark and leaves, or deliberately whitewashed trunks. Whether the growth is crusty, cottony, or powdery tells you which one, and lichen itself never needs treatment. Read the guide →

Still not sure? Compare with these clues

Home Exterior Clues Round Holes in Wood With Sawdust: Bees, Ants, or Beetles? A perfectly round hole about 1/2 inch across with a pile of coarse sawdust beneath it is the signature of carpenter bees, especially on bare or weathered wood. Fine sawdust-like debris coming from cracks and seams rather than a drilled hole points to carpenter ants, while clusters of much smaller holes are usually old wood-boring beetle exits. The hole's size, the texture of the sawdust, and whether you see insect traffic will tell you which one you have. Read the guide → Home Exterior Clues Woodpecker Holes in Siding: Why They Drill and How to Stop It Holes pecked in your siding usually mean a woodpecker is foraging for insects, drumming to claim territory, or excavating a nest cavity — and rows of small holes often signal that insects like carpenter bee larvae are already living in the wood. A single clean half-inch round hole with sawdust below it, on the other hand, is typically the work of carpenter bees themselves. Because woodpeckers are federally protected, the fix is deterrence and repair, never harm. Read the guide →