The top wood-boring insects that will harm your trees are beetles and moths whose larvae tunnel beneath the bark to feed on living tissue. As they chew through the cambium layer, they cut off the flow of water and nutrients, which starves the canopy and eventually kills the tree.
Adults get the attention because they’re visible, but the larvae do nearly all of the structural damage, carving galleries through the cambium and sapwood for months or even years before a canopy begins to thin.
Entomologists sort these pests into two groups, and the difference matters:
- Primary invaders attack healthy, vigorous trees. Emerald ash borer is the best-known example.
- Secondary invaders target trees already weakened by drought, construction damage, compacted soil, or storm injury.
Watch for these warning signs on trunks and larger limbs:
- D-shaped or round exit holes in the bark
- Sawdust-like frass packed in bark crevices or at the base
- Bark splitting, cracking, or sloughing off in patches
- Heavy woodpecker activity concentrated on one trunk
- Canopy dieback that starts at the top and works downward
Boring damage is usually well advanced before anything shows up in the leaves. That lag is exactly why the annual inspections Red’s Tree Service recommends catch problems a quick glance from the driveway will always miss.
The 6 Wood Boring Insects Most Likely to Damage Your Trees
Six pests account for most of the borer calls our expert team responds to. Some drill directly into wood. Others strip the canopy first and open the door for borers to move in behind them.
1. Emerald Ash Borer
This metallic green beetle is the most destructive of the group. Females lay eggs in bark crevices, and the larvae feed in S-shaped galleries just under the bark. Adults leave a distinctive D-shaped exit hole about an eighth of an inch wide. An untreated ash tree typically dies within two to four years of infestation, often starting with dieback in the upper canopy and shoots sprouting from the lower trunk. Emerald ash borer has been confirmed across much of the region, so any untreated ash on your property deserves an assessment.
2. Gypsy Moth (Spongy Moth)
Spongy moth caterpillars don’t bore, they defoliate. Heavy feeding on oaks strips the canopy in late spring, forcing the tree to burn through stored energy to push out a second flush of leaves. Repeated defoliation leaves oaks wide open to secondary borers and root disease. Look for tan, fuzzy egg masses on trunks, fences, and firewood stacks.
3. Locust Borer
Black locust is this beetle’s only real host. Larvae tunnel into the trunk and branches, and the tree responds with swollen, cracked scars around each wound. Those scars weaken limb attachments and trunk wood, which is why locust borer damage so often ends in a snapped branch during a summer thunderstorm.
4. Longhorn Beetles (Roundheaded Borers)
Named for their long antennae, these beetles produce large, round exit holes and wide tunnels that run deep into the sapwood. Maple, birch, and hardwoods stressed by drought or construction are frequent targets. Coarse, fibrous frass pushed out of the trunk is a reliable clue.
5. Elm Bark Beetle
The beetle itself causes modest damage. The fungus it carries is the real threat. Elm bark beetles spread Dutch elm disease from tree to tree as they feed, and infected elms wilt and yellow, usually one branch or one side first. Removing dead and dying elm wood promptly breaks the cycle.
6. Tent Caterpillars
Silk nests in branch forks are the giveaway. Eastern tent caterpillars feed heavily on cherry, apple, and crabapple in early spring, and a stripped canopy year after year leaves those trees vulnerable to flatheaded borers and canker fungi.
| Insect | Trees Most at Risk | Telltale Sign | Threat Level |
|---|---|---|---|
| Emerald ash borer | Ash | D-shaped exit holes, top-down dieback | Usually fatal without treatment |
| Spongy moth | Oak, other hardwoods | Fuzzy egg masses, spring defoliation | Weakens tree, invites borers |
| Locust borer | Black locust | Swollen trunk scars, limb failure | Structural hazard |
| Longhorn beetles | Maple, birch, stressed hardwoods | Round exit holes, coarse frass | Serious in declining trees |
| Elm bark beetle | Elm | Wilting on one side, bark galleries | Spreads Dutch elm disease |
| Tent caterpillars | Cherry, apple, crabapple | Silk nests in branch forks | Stress, rarely fatal alone |
Why Early Borer Detection Protects Your Trees and Property
Timing decides the outcome. An ash tree caught in the first year of an emerald ash borer infestation often responds well to a systemic trunk injection. That same tree, two years later with half its canopy gone, rarely recovers no matter what you spend on it. Our certified arborists, backed by our membership in the International Society of Arboriculture (ISA), look for that window on every inspection and tell you plainly when it has already closed.
Early detection pays off in several ways:
- Treatment stays on the table. Late-stage tunneling destroys the vascular tissue permanently, and no product rebuilds it.
- You avoid removal and replacement. Taking down a mature shade tree and planting a replacement that needs decades to fill the same space costs far more than a season of preventive care. See our tree removal page for what that process involves.
- Hazards get addressed before storms find them. Borer-weakened limbs and hollowed trunks fail in wind, and a failure over a roof, driveway, or fence line becomes a liability problem fast.
- Healthy trees defend themselves. Well-watered, properly mulched, deep-root fertilized trees fend off secondary borers that would overwhelm a stressed neighbor.
- Nearby trees stay protected. Elm bark beetles and emerald ash borer both move quickly through a stand, so monitoring one tree often saves three.
A twenty-minute walk around your trunks each spring can save you time and catastrophe, because a borer caught in year one is a trunk injection instead of a crane removal over your roof. Heading into storm season with that inspection behind you also gives you peace of mind that your property is safe.
Borer Damage vs. Other Tree Problems: How to Tell the Difference
Thinning leaves and dead branches show up with almost every tree problem, so the leaves alone won’t tell you much. The trunk and bark will. Here’s how the main causes separate out:
| Symptom | Wood Boring Insects | Fungal Disease | Drought / Root Stress |
|---|---|---|---|
| Exit holes in bark | Yes, D-shaped or round | No | No |
| Frass or sawdust | Present in bark cracks | Absent | Absent |
| Woodpecker activity | Heavy, focused on trunk | Minimal | Minimal |
| Dieback pattern | Top down, branch tips first | One side or one limb | Uniform across canopy |
| Leaf appearance | Small, sparse, off-color | Spots, blotches, cankers | Scorched or curled margins |
| Trunk findings | Galleries under loose bark | Oozing cankers, fruiting bodies | Cracked soil, girdling roots |
Peel back a piece of loose bark on a suspect limb. Winding galleries packed with fine sawdust point to borers. Discolored, water-stained wood without tunnels usually points to a vascular disease instead.
Keep in mind that these problems overlap constantly. Borers follow stress, so a tree damaged by drought one summer or trenched during a patio installation may show root problems and borer activity at the same time. Sorting out which came first shapes the treatment plan, and that’s the kind of call a trained and certified arborist makes on site.
What Affects the Cost of Borer Treatment and Tree Removal
Borer treatment and tree removal costs depend mostly on tree size and species, the number of infested trees, the treatment method your arborist recommends, and how close the tree sits to a house, fence, or power line. Stump grinding and thorough cleanup are usually priced separately.
The main factors we evaluate during a free quote:
- Tree size and species. Trunk diameter drives treatment dosing, and larger canopies take more time and rigging to remove safely.
- Number of affected trees. A row of ash trees along a property line is priced differently than a single specimen.
- Treatment method. Soil drenches, basal bark sprays, and trunk injections differ in cost and in how long each application lasts.
- Extent of canopy loss. Once dieback passes a certain point, treatment stops being the economical choice and removal becomes the recommendation.
- Site access and obstacles. Backyard trees over a pool, a shed, or utility lines require more equipment, more crew, and careful sectional dismantling.
- Cleanup scope. Stump grinding, chipping, and thorough cleanup can be bundled or handled as add-ons depending on what you want left behind.
Treatment programs are ongoing rather than one-and-done. Systemic products protect for a set number of seasons, so budgeting for repeat applications is part of any real plan for a high-value ash. During a free quote, the certified arborists at Red’s Tree Service walk the property, measure trunk diameter, note the obstacles our crew will have to work around, and lay the treatment cost and the removal cost side by side so the comparison is an easy one to make.
Which Trees Can Still Be Saved from Borers?
Trees with less than about 30% canopy dieback, a solid trunk, and an early-stage infestation can often be saved with systemic treatment and supportive care. Once tunneling is extensive, the trunk sounds hollow, or major limbs have died, removal is the safer recommendation. A certified arborist assessment settles the question.
Good candidates for treatment generally share these traits:
- Less than roughly 30% dieback in the upper canopy
- Firm, intact bark with no large areas of loose or missing bark
- Few exit holes, concentrated rather than covering the trunk
- An ash tree growing near a confirmed emerald ash borer infestation, treated preventively before symptoms appear
- Enough root space and soil moisture to support a new flush of growth after treatment
- High value to the property, such as a mature shade tree cooling the south side of a house or an anchor tree in a yard design
Removal is usually the right call when we find widespread galleries under the bark, a hollow or spongy trunk, mushrooms at the root flare, or the loss of a primary structural limb. At that stage the tree isn’t just declining, it’s a hazard sitting above something you care about, and waiting another season only makes the takedown more difficult.
Because an honest read beats a guess every time, the arborists at Red’s Tree Service perform a tree risk assessment before recommending either path. We sound the trunk, measure how much canopy has been lost, check the root flare, and then put either a dated treatment schedule or a removal plan in writing so our clients make the most informed decisions for their trees.
Working With Certified Arborists on Borer Problems
Red’s Tree Service is a family owned and operated business and a locally owned and operated tree service provider, providing quality tree services for over 40 years. We keep a trained and certified arborist on staff, back our crews with an extensive employee training program, and hold memberships with the International Society of Arboriculture (ISA), the Southern Chapter of Urban Forestry, and the Tennessee Urban Forestry Council. We’re also BBB accredited.
If you’ve spotted exit holes, frass, or a canopy thinning from the top down, our expert team can inspect the tree, identify which insect is responsible, and explain what your realistic options are at that stage of infestation. A borer assessment rarely takes more than an hour: we sound the trunk, check the root flare, look under loose bark for galleries, and estimate how much canopy has already been lost. From there you’ll know whether you’re looking at a treatment candidate, a tree worth monitoring for another season, or a removal. We also return emergency tree care calls 24 hours a day, which matters when a borer-weakened limb decides to fail before that conversation ever happens.
Frequently Asked Questions About Wood Boring Insects
How do I know if my tree has borers?
Check the trunk and large limbs for exit holes, fine sawdust-like frass in bark crevices, and patches of bark that have split or fallen away. Sudden, heavy woodpecker activity on one tree is another strong clue, since woodpeckers hunt the larvae. Peeling back a loose piece of bark and finding winding tunnels confirms it.
Can a tree recover from wood boring insects?
Yes, if the infestation is caught early and the vascular tissue is largely intact. Systemic treatment combined with proper watering, mulching, and deep root fertilization gives the tree the resources to compartmentalize the wounds and rebuild its canopy. Trees that have already lost more than a third of their canopy rarely bounce back.
What time of year do borers attack trees?
Most adult borers emerge and lay eggs from late spring through summer, with emerald ash borer adults typically active from May into August. Larvae then feed inside the wood through fall and winter. Preventive treatments are usually timed for spring, before or during the egg-laying window, so the product is in place when larvae begin feeding.
Do borers spread to nearby trees?
They do, and quickly with some species. Emerald ash borer adults fly to new ash trees within a few miles, and elm bark beetles carry Dutch elm disease directly from an infected elm to a healthy one. When one tree is confirmed infested, every susceptible tree on the property should be inspected.
Should I remove a tree infested with borers?
Removal makes sense when the trunk is hollow or extensively tunneled, when more than about half the canopy has died, or when the tree could fall on a house, driveway, or power line. Dead borer-killed trees become brittle fast, which makes them more dangerous and more expensive to take down later.
Does mulch or firewood spread wood boring insects?
Firewood is one of the most common ways borers travel long distances, which is why forestry agencies recommend buying firewood where you plan to burn it and never hauling it across county or state lines. Properly processed and composted mulch poses very little risk. Storing unsplit, bark-on logs against your house does.