Common Tree Pests in MA

In 30 years of tree work across Middlesex County, I have watched entire species get wiped out by bugs that were not even here when I started this business. The emerald ash borer alone has changed the landscape of every town in our service area. Here is a field guide to the pests that are actively killing trees in Massachusetts — what they look like, what they attack, and what you can actually do about them.

Emerald Ash Borer (Agrilus planipennis)

What It Looks Like

The adult beetle is metallic green, about half an inch long, and shaped like a tiny bullet. You will rarely see the adults. What you will see are the signs they leave behind: D-shaped exit holes in the bark (about the size of a pencil eraser), S-shaped larval galleries under the bark, and bark that splits and peels as the tree declines. Increased woodpecker activity is often the first noticeable sign — the birds are digging for larvae under the bark.

What It Attacks

All species of ash — white ash, green ash, and black ash. No ash tree in Massachusetts is safe unless it is being actively treated with trunk injections.

What Happens

The larvae feed under the bark in the cambium layer, creating winding galleries that cut off the tree's ability to transport water and nutrients. An infested tree typically dies within 3 to 5 years. Canopy dieback starts at the top and works down. By the time the lower branches are bare, the tree is dead and becoming structurally dangerous. We have a detailed guide on the emerald ash borer and what homeowners need to know.

Can the Tree Be Saved?

If caught early — less than 30 percent canopy loss — trunk injections with emamectin benzoate can save the tree, but it requires treatment every 2 years indefinitely ($200 to $400 per treatment). If the tree has lost more than 50 percent of its canopy, it is too late. Removal is the only safe option. I would estimate that 90 percent of the ash trees we are called about are past the point of saving. In Billerica and Tewksbury, the ash borer has killed the vast majority of untreated ash trees.

Winter Moth (Operophtera brumata)

What It Looks Like

The adults are small, light brown moths that are active in late November and December — you see them fluttering around porch lights on mild winter evenings. The caterpillars are small, pale green inchworms that emerge in spring just as leaf buds are opening. The caterpillars bore into the buds and eat the leaves before they even unfurl, which is what makes them so destructive.

What It Attacks

Primarily oaks (red oak, white oak, pin oak), but also maples, crabapples, blueberries, and other deciduous species. Oaks take the worst hit because the timing of bud break coincides perfectly with caterpillar emergence.

What Happens

In a bad year, entire canopies get stripped bare in May. The trees push out a second set of leaves in June and July, but that costs enormous energy. After 3 to 4 consecutive years of heavy defoliation, the tree is so weakened that it cannot fight off opportunistic diseases like Armillaria root rot and two-lined chestnut borer, which deliver the killing blow.

I watched this play out across Chelmsford and Billerica over a five-year stretch. Neighborhoods full of beautiful oaks that thinned out a little more every spring. By year four or five, we were removing dead oaks that had been healthy trees just a few years earlier. The biological control program using a parasitic fly (Cyzenis albicans) has started reducing winter moth populations in some areas, but the damage to weakened trees is already done.

Can the Tree Be Saved?

Healthy oaks can survive a few years of defoliation. Targeted pesticide applications (trunk injections or foliar sprays) timed to caterpillar emergence in spring can protect high-value trees. If a tree has been defoliated 3 or more years in a row and is showing significant canopy dieback, it may be too late.

Spongy Moth (Lymantria dispar) — Formerly Gypsy Moth

What It Looks Like

The caterpillars are large and distinctive: dark-colored with pairs of blue and red dots running down their back, covered in tufts of hair. The egg masses are tan, fuzzy patches about the size of a quarter to a silver dollar, found on tree trunks, branches, fences, and the sides of buildings. The male moths are brown and fly; the females are white with dark markings and do not fly.

What It Attacks

Almost everything, but particularly oaks, aspens, birches, willows, and crabapples. During outbreak years, they will eat nearly any deciduous tree. They avoid ash, tulip tree, and most conifers.

What Happens

During outbreak years, spongy moth caterpillars can completely defoliate large areas of forest and residential trees. Massachusetts had a catastrophic outbreak in 2015 to 2017 that stripped millions of acres of canopy. Trees that were already stressed from drought and winter moth damage were hit hardest. Like winter moth, the defoliation itself does not always kill the tree, but it weakens it severely and secondary stressors finish it off.

Can the Tree Be Saved?

Healthy trees can tolerate one year of heavy defoliation. Two consecutive years is stressful. Three or more is often fatal, especially for oaks that are also dealing with winter moth and drought. Removing egg masses in winter, using burlap bands to trap caterpillars, and targeted Bt (Bacillus thuringiensis) sprays are all management options. For high-value trees near your home, contact a licensed applicator for spray programs.

Asian Longhorned Beetle (Anoplophora glabripennis)

What It Looks Like

Large (1 to 1.5 inches), jet black with irregular white spots, and very long antennae banded in black and white. Unmistakable if you see one. Exit holes are perfectly round and about the diameter of a dime or larger — much bigger than emerald ash borer's D-shaped holes.

What It Attacks

Maples are the primary target — sugar maple, red maple, silver maple, Norway maple, and boxelder. Also attacks birch, elm, willow, horse chestnut, and several other hardwoods.

What Happens

The larvae bore deep into the heartwood, destroying the tree's structural integrity from the inside out. There is no treatment that can save a heavily infested tree. The Worcester infestation, discovered in 2008, required cutting down over 30,000 trees in a multi-year federal eradication effort. As of 2024, the USDA declared the Worcester quarantine area eradicated, but the beetle could reappear anywhere through imported wood products.

Can the Tree Be Saved?

No. If an Asian longhorned beetle infestation is confirmed, the tree must come down and the wood must be destroyed (chipped or burned). This is a federally regulated pest. If you see this beetle or its signs — round exit holes, sawdust-like frass at the base, branch dieback — report it to the USDA at 1-866-702-9938 or the Massachusetts Department of Conservation and Recreation. Do not ignore it.

Hemlock Woolly Adelgid (Adelges tsugae)

What It Looks Like

Look at the underside of hemlock branches where the needles attach to the twigs. If you see small, white, cotton-ball-like masses, that is hemlock woolly adelgid. Each mass is about the size of a pencil eraser tip. They are most visible in late fall through spring.

What It Attacks

Eastern hemlock and Carolina hemlock exclusively. Eastern hemlock is a common ornamental and forest tree throughout Massachusetts.

What Happens

The adelgid feeds on the sap at the base of hemlock needles, causing needle drop, branch dieback, and eventually tree death over a period of 4 to 10 years. Hemlocks in shaded, moist locations tend to survive longer than those in exposed, dry sites. I have seen beautiful hemlock groves in Carlisle and Westford that have been devastated by this pest.

Can the Tree Be Saved?

Yes, if caught before severe decline. Trunk injections of imidacloprid or dinotefuran are effective and can protect a hemlock for 3 to 5 years. Horticultural oil sprays can also reduce populations. Hemlocks are worth saving if they are important to your landscape — they provide year-round screening and are difficult to replace. If the tree has lost more than 70 percent of its needles, it is unlikely to recover even with treatment.

Eastern Tent Caterpillar (Malacosoma americanum)

What It Looks Like

These caterpillars build conspicuous white, silky tent-like webs in the crotches of branches, usually in spring. The caterpillars are dark with a white stripe down the back and blue and brown markings. The tents start small and grow as the caterpillars mature.

What It Attacks

Wild cherry, crabapple, apple, and occasionally other fruit trees and ornamentals.

What Happens

Eastern tent caterpillars defoliate sections of the tree, starting from the tent location. They are messy and unsightly but rarely kill trees. Healthy trees re-leaf after the caterpillars are done feeding in late spring. The aesthetic damage is worse than the actual harm to the tree.

Can the Tree Be Saved?

Almost always. You can remove the tent webs by hand in early morning when caterpillars are inside (wear gloves and dispose of them). Pruning out heavily infested branches is effective for small infestations. In most cases, no chemical treatment is needed. I tell homeowners not to panic about tent caterpillars — they look terrible for a few weeks in May but the tree will be fine.

What Should You Actually Do?

Here is my practical advice after three decades of dealing with pest-damaged trees:

• Learn to identify what you have. Take 10 minutes to check your trees each spring and fall. Look for exit holes, unusual leaf damage, egg masses, and fungal growth. Early detection is the difference between saving a tree and removing a dead one.
• Know which trees are high-risk. If you have ash, hemlock, or oak on your property, those are the species under the most pressure right now in Massachusetts.
• Do not panic about every caterpillar. Tent caterpillars and other native defoliators are part of the ecosystem. Most healthy trees handle them fine.
• Get treatment for high-value trees. If you have a beautiful hemlock screen or a heritage oak, proactive trunk injection treatments are worth the investment.
• Remove dead trees promptly. A dead tree is a falling tree. It is just a question of when. Dead ash trees in particular become brittle very quickly and drop large branches without warning. Read about why trees die for more on the decline process.

McDonald Tree Service handles pest-damaged and dead tree removals across all 13 towns in our service area: Billerica, Chelmsford, Lowell, Tewksbury, Wilmington, Burlington, Bedford, Carlisle, Dracut, Westford, Andover, Woburn, and Lexington. If you have a tree you are worried about, call (978) 375-2272 for a free assessment. We will tell you honestly whether the tree can be saved or whether it needs to come down.