Maine’s forests face an unprecedented threat. Over the past two decades, invasive insects have spread across the state, killing thousands of ash trees, weakening hemlocks along the coast, and threatening the economic and ecological foundation of the Pine Tree State.
You might already have these destructive pests in your yard without knowing it. This guide shows you exactly what to look for, where these insects hide, and how to report them to help protect Maine’s trees before it’s too late.
1. Emerald Ash Borer
The emerald ash borer (Agrilus planipennis) arrived in Maine in 2018, first detected in Madawaska. Since then, this metallic green beetle has confirmed its presence in multiple southern Maine communities and expanded to Mount Desert Island as of 2025. The beetle’s larvae create devastating damage by burrowing under ash tree bark, cutting off the tree’s ability to transport water and nutrients.
You’ll recognize adult beetles by their brilliant emerald-green coloring and compact size, measuring less than half an inch long. The most telling signs of infestation appear on the tree itself: look for distinctive D-shaped exit holes in the bark, approximately 1/8 inch in diameter. Underneath loose bark, you’ll find S-shaped galleries filled with frass, a sawdust-like waste material. Woodpeckers often strip outer bark in vertical strips—called “woodpecker blonding”—as they hunt for larvae beneath the surface.
Pro Tip: Maine’s native tiger beetle resembles the emerald ash borer but has noticeably larger eyes, longer antennae and legs, and a slightly different body shape. When in doubt, photograph the insect and report it.
The state maintains an active quarantine zone that now includes all towns on Mount Desert Island. Moving firewood from quarantined areas can spread the beetle to new locations, so always buy firewood where you’ll burn it. If you suspect an emerald ash borer infestation, report it immediately at maine.gov/eab or call the national hotline at 1-866-322-4512.
2. Browntail Moth
Browntail moth (Euproctia chrysorrhoea) caterpillars pose both ecological and health threats to Maine residents. These invasive insects build distinctive overwintering nests on the tips of tree branches, particularly on oak, apple, cherry, and other hardwood species. The caterpillars emerge in spring with toxic hairs that cause severe skin rashes, respiratory problems, and eye irritation in humans.
Winter provides the best opportunity for identification and removal. Look for silken nests at branch tips—they appear as clusters of dead leaves bound together with webbing. These nests typically measure 1-2 inches long and contain several hundred caterpillars that will emerge when temperatures warm. The caterpillars themselves display dark brown bodies with distinctive white dashes along their sides and two bright red dots on their backs.
The toxic hairs remain dangerous even after the caterpillars transform into moths. Wind can carry these microscopic hairs considerable distances, affecting people who never directly contact the insects. Peak health impacts typically occur from late May through mid-July when caterpillars are most active.
Remove nests during winter months by cutting the affected branch tips and placing them in a bucket of soapy water—this is the safest disposal method. Never burn nests, as this releases toxic hairs into the air. You can report browntail moth sightings through the Maine Department of Agriculture, Conservation and Forestry’s online form at maine.gov. During removal, wear protective clothing, gloves, and a mask to avoid contact with any remaining hairs.
3. Hemlock Woolly Adelgid
Hemlock woolly adelgid (Adelges tsugae) has established populations throughout southern and coastal Maine, spreading from Kittery to Mount Desert Island since its accidental introduction from Japan in the 1950s. This tiny, aphid-like insect feeds on hemlock sap, causing needles to dry out, fade to grayish-green, and eventually drop from the tree.
The adelgid’s distinctive appearance makes identification straightforward. Look for white, cottony masses on the undersides of hemlock twigs at the bases of needles—not on the needles themselves, but where they attach to the branch. These woolly coverings resemble tiny cotton balls and are most visible from late October through July. Each mass contains dozens of adelgids protected by waxy white filaments.
Important Note: The state has established quarantine zones covering all of York, Lincoln, and Sagadahoc counties, plus portions of Androscoggin, Cumberland, and Kennebec counties. These regulations restrict the movement of hemlock plants and products to prevent spread to uninfested areas.
Hemlock decline progresses systematically, starting with the lowest branches and moving upward through the crown. Trees may survive for several years with light infestations, but heavy populations can kill hemlocks within 4-10 years. The presence of elongate hemlock scale, another invasive pest, can accelerate decline. Winter months offer the best time for hemlock work, as the adelgid is least likely to be in egg or mobile crawler stages that could spread during disturbance.
Report hemlock woolly adelgid sightings to the Maine Forest Service at 207-287-2431. Early detection helps officials track the adelgid’s spread and implement management strategies before entire hemlock stands succumb to infestation.
4. Winter Moth
Winter moth (Operophtera brumata) caterpillars emerge in early spring to feed on buds and developing leaves of various trees and shrubs, with particular preference for oaks, maples, apples, blueberries, and crabapples. The moths themselves fly during winter months, often when snow is on the ground—hence the Maine Forest Service’s memorable phrase: “When moths fly with snow, let the Maine Forest Service know!”
Adult males have tan to brown wings and fly readily, while females are nearly wingless and must crawl up tree trunks to lay their eggs. The caterpillars appear light green with a white stripe along each side and grow to approximately one inch long. They feed voraciously from bud break through June, causing defoliation that weakens trees and reduces fruit production in orchards.
Tree banding provides effective monitoring and control. Wrap a sticky barrier around tree trunks in late fall to capture females as they crawl upward to lay eggs. The Town of Harpswell and UMass Extension have published helpful instructions for proper banding techniques that maximize capture rates without harming the tree.
Severe defoliation occurs when winter moth populations reach high densities. Trees may produce a second flush of leaves in summer, but this requires significant energy reserves and can stress trees already weakened by other factors. Commercial blueberry operations in New England have reported significant crop losses during outbreak years. You can report winter moth observations by completing the Maine Department of Agriculture, Conservation and Forestry’s winter web survey form, available at maine.gov.
5. Spongy Moth
The spongy moth (Lymantria dispar), formerly known as gypsy moth, causes periodic outbreak defoliations across Maine’s forests. This invasive insect particularly targets oak trees but will feed on over 300 different tree and shrub species when populations are high. Adult males fly actively in summer, while larger females cannot fly despite having wings.
Egg masses provide the easiest identification feature. Females lay these masses on tree bark, rocks, outdoor furniture, vehicles, and virtually any outdoor surface. Each mass appears tan or buff-colored, roughly oval-shaped, and covered with fuzzy hair from the female’s abdomen. A single mass contains 400-600 eggs that will hatch in spring.
The caterpillars display distinctive markings: five pairs of blue dots followed by six pairs of red dots along their backs, with a covering of long hairs across their bodies. They grow to approximately 2.5 inches long before pupating. Feeding occurs primarily from May through early July, with peak defoliation typically in June.
Key Insight: Spongy moth populations cycle naturally, with outbreak years followed by collapse due to disease and predation. However, repeated defoliations can kill trees, particularly when combined with drought stress or other invasive pest damage.
The insect’s ability to lay eggs on any surface makes it an expert hitchhiker. Always inspect vehicles, camping equipment, and outdoor furniture when traveling to or from infested areas. Scrape egg masses into soapy water for disposal—crushing releases viable eggs. Contact the Maine Forest Service at foresthealth@maine.gov to report significant defoliation or unusual population increases.
6. Asian Longhorned Beetle
Asian longhorned beetle (Anoplophora glabripennis) has not yet been confirmed in Maine, but officials maintain active surveillance due to the insect’s devastating potential. This large beetle, measuring over one inch long, displays a striking appearance: shiny black body with distinctive white spots and very long antennae banded in black and white.
The beetle attacks maple, birch, elm, and other hardwood species. Females chew oval to round pits in the bark to deposit eggs. Larvae bore deep into the wood, creating extensive tunnel systems that compromise structural integrity and eventually kill the tree. Adult beetles emerge through perfectly round exit holes approximately 3/8 inch in diameter, leaving piles of coarse sawdust at the tree base.
Look for these warning signs: fresh, light-colored oval wounds on branches and trunks where females have chewed egg-laying sites; round exit holes larger than those created by native borers; sawdust accumulation at the tree base or in branch crotches; and unexplained dieback in otherwise healthy-looking hardwood trees. The larvae create packed galleries filled with sawdust-like material visible under loose bark.
Common Mistake: Many people confuse Asian longhorned beetle with native long-horned beetles. Key differences include the Asian beetle’s smooth, polished appearance and white spots arranged in a specific pattern, whereas native species typically have rough texture and different coloring patterns.
Early detection is absolutely critical. This beetle has caused quarantines and massive tree removal programs in other states where it has established. If you find a suspected Asian longhorned beetle, capture it carefully in a rigid container, take clear photographs showing all angles, and immediately contact the Maine Forest Service at foresthealth@maine.gov. Do not transport the insect or infested wood, as this can spread the infestation.
7. Brown Marmorated Stink Bug
Brown marmorated stink bug (Halyomorpha halys) has been detected in Maine but is not yet established in outdoor populations. This shield-shaped insect measures approximately 5/8 inch long with a mottled brown appearance. The distinctive feature is alternating light and dark bands on the antennae and a white or light-colored stripe on the last two segments.
While primarily a nuisance pest that invades homes in fall seeking overwintering sites, brown marmorated stink bugs can cause significant agricultural damage. They feed on developing fruits, vegetables, and field crops by piercing plant tissue and sucking out fluids. This creates sunken, dimpled areas on fruit surfaces and can transmit plant diseases. Affected fruits develop discolored, corky tissue under the feeding sites, making them unmarketable.
The stink bug earned its name from the foul-smelling chemical it releases when crushed or threatened. This odor serves as a defense mechanism against predators but creates an unpleasant experience for homeowners dealing with indoor invasions. Large numbers may congregate on the warm sides of buildings during fall before finding entry points.
Maine’s current detection status means preventing establishment is still possible. The state monitors for this pest through survey traps and public reports. If you find brown marmorated stink bugs, especially outdoors during the growing season, report them to the Maine Department of Agriculture, Conservation and Forestry. Avoid crushing the insects; instead, vacuum them up or sweep them into soapy water for disposal.
8. Spotted Lanternfly
Spotted lanternfly (Lycorma delicatula) egg masses were discovered on trees shipped from Pennsylvania to several Maine communities, including Boothbay, Freeport, Northeast Harbor, and Yarmouth. While not yet established in Maine’s outdoor environment, this colorful planthopper poses a significant threat to grapes, hops, fruit trees, and hardwood forests.
Adult spotted lanternflies display unmistakable coloring: approximately one inch long with gray forewings covered in black spots. When they spread their wings, you’ll see brilliant red underwings with black spots and white patches. Nymphs progress through several stages, starting small and black with white spots, then developing red patches before reaching adulthood.
The egg masses create the greatest concern for Maine. Females lay rectangular, inch-long masses containing 30-50 eggs, covering them with a gray, waxy coating that resembles dried mud or a smear of old putty. These masses appear on tree bark, outdoor furniture, vehicles, stone, and virtually any outdoor surface. The insect is an expert hitchhiker—egg masses can survive long-distance transport and establish new populations far from their origin.
Pro Tip: Anyone who received plants, landscaping materials, or outdoor furniture from states with known spotted lanternfly infestations should carefully inspect all items and packaging. The egg-laying season runs from fall through early spring, making this the highest-risk period for accidental transport.
Spotted lanternfly feeds on plant sap, weakening trees and vines. Heavy feeding produces copious amounts of honeydew, a sticky substance that promotes sooty mold growth and attracts other insects. In established populations, the honeydew can coat surfaces underneath infested trees, creating nuisance problems for anyone working or living below.
If you find any life stage of spotted lanternfly, take clear photographs, collect a specimen if possible, and report immediately to bugwatch@maine.gov. Include location details and information about any materials recently received from out-of-state sources. Maine’s status as an early-detection state means your report could prevent this destructive pest from establishing breeding populations.
Conclusion
Maine’s network of forests, parks, and backyards faces continuous pressure from invasive insects. Your vigilance makes a meaningful difference in early detection efforts that can prevent widespread infestations and save thousands of trees. The Maine Forest Service, Department of Agriculture, Conservation and Forestry, and University of Maine Cooperative Extension rely on public reports to track pest movements and implement timely responses.
Governor Janet Mills proclaimed February 24 – March 2 as Invasive Species Awareness Week in Maine, recognizing that education and community engagement are fundamental to protecting the state’s natural resources. Trees provide countless benefits: clean air and water, wildlife habitat, recreation opportunities, and economic value through forestry and tourism. Losing these resources to invasive pests would fundamentally alter Maine’s landscape and economy.
What You Can Do Today:
Spend 10 minutes examining trees in your yard and neighborhood for signs of invasive insects. Look for unusual holes, sawdust accumulations, white cottony masses, or unexplained dieback. Take photographs of anything suspicious, place a coin or ruler in the frame for scale, and report findings to the appropriate agency.
Buy firewood locally and burn it where you purchase it. Moving firewood is one of the primary ways invasive insects spread to new areas. Even seemingly dry, dead wood can harbor dormant insects or eggs ready to emerge in a new location.
Inspect vehicles, camping equipment, and outdoor items when traveling. Invasive insects and their egg masses can attach to any surface. A quick check and wipe-down before leaving infested areas prevents accidental transport.
Learn to identify common invasive insects in your region. The Maine Forest Service website at maine.gov/forestpests provides detailed identification guides, distribution maps, and current threat assessments. Understanding what to look for makes you an effective early detection partner.
Join community science efforts through programs like iNaturalist, where you can document and share insect observations. These platforms connect you with experts who can verify identifications and contribute your findings to scientific databases tracking insect distributions and population trends.
Maine’s forests have survived ice storms, droughts, and natural pest cycles for thousands of years. With community awareness and rapid response to new threats, these forests can continue thriving for future generations. Your role in this effort—whether through careful observation, timely reporting, or responsible firewood practices—helps preserve the Pine Tree State’s most valuable natural resource.
