8 Types of Caterpillars in Maine (And How to Identify Them)

Maine’s forests and gardens host a surprising variety of caterpillars, from harmless tent-builders to a species whose hairs can trigger a poison-ivy-like rash. Learning to identify caterpillar species in Maine helps homeowners protect their trees, gardeners spot butterfly caterpillars before they strip a plant, and hikers avoid an unpleasant surprise on a summer trail. Whether these larvae are chewing through a maple canopy or building silk tents in an old apple tree, each one has a distinct look and a story worth knowing.

This guide walks through eight native caterpillars in Maine and a few notable non-native arrivals, covering what they eat, where they show up, and how to tell them apart. For readers curious about how these species compare to caterpillars in other regions, the broader world of types of caterpillars found across North America offers useful context, and the sheer diversity becomes clearer once you consider how different Maine’s cool forests are from tropical ecosystems like the Amazon rainforest’s insect life.

Caterpillar	Primary Host Plants	Key Identifying Feature	Active Season in Maine
Eastern Tent Caterpillar	Wild cherry, apple	White stripe down the back, blue side spots	April–June
Forest Tent Caterpillar	Oak, poplar, maple, birch	Keyhole-shaped white spots, no true tent	May–June
Spongy Caterpillar	Oak and many hardwoods	Hairy body with blue and red spot pairs	May–July
Browntail Caterpillar	Oak, beech, birch, rose-family shrubs	Broken white stripes, two orange dots near tail	April–late June
Io Moth Caterpillar	Wide variety of trees and shrubs	Bright green with red-and-white side stripe	Two broods, spring and summer
Monarch Caterpillar	Milkweed only	Black, white, and yellow bands	Summer
Variable Oakleaf Caterpillar	Oak, beech, sugar maple	Highly variable coloring, often mottled brown	Late summer
Orangehumped Mapleworm	Sugar maple, beech	Yellow-orange hump behind the head	Late summer

1. Eastern Tent Caterpillar

The Eastern tent caterpillar (Malacosoma americanum) is one of two native tent-building species found across the state. Coastal Maine Botanical Gardens notes that Maine is home to many different tent-building caterpillars—some native, like the Eastern tent or forest tent caterpillars, or non-native or introduced species, like the spongey and browntail moths.

This species builds its silk nest in the crooks of tree branches rather than at the branch tips, and the structure falls apart on its own well before the growing season ends. As the Botanical Gardens explains, Eastern tent caterpillars are far more likely to make their nests in the crooks of branches, and their tents break down in late summer. That timing makes them easy to distinguish from browntail moth nests, which persist through winter.

Wild cherry trees are the preferred host, though the caterpillars will also feed on apple and crabapple. Despite their sometimes dramatic tents, Eastern tent caterpillars rarely cause lasting harm to established trees, and healthy hardwoods typically releaf without issue the following spring.

2. Forest Tent Caterpillar

Confusingly, the forest tent caterpillar (Malacosoma disstria) does not actually build a tent. Instead, this native species spins a silk mat on the trunk or a branch where the colony rests between feeding bouts. As the Botanical Gardens points out, forest tent caterpillars do not make webs, which is the opposite of what many people expect from a “tent” caterpillar.

This species has a broader appetite than its Eastern cousin. According to one Maine-focused overview of native caterpillar species, Maine has two tenting caterpillar species: the forest tent and the eastern tent, and forest tent caterpillars prefer oak, poplar, maple and birch trees. Large populations can strip whole stands of hardwoods bare in a bad year, though most trees recover with a second flush of leaves by midsummer.

Forest tent caterpillar outbreaks tend to run in cycles lasting several years before natural predators and disease bring numbers back down. Readers who want to see how this same genus behaves further north can compare notes with caterpillar and moth populations documented among insects in Canada, where forest tent caterpillar outbreaks are also a recurring forestry concern.

3. Spongy Caterpillar

The spongy caterpillar (Lymantria dispar) is a non-native species that arrived in North America from Europe and is still commonly recognized by its older name, the gypsy moth caterpillar. Unlike the true tent caterpillars, this species is heavily bristled, with rows of blue and red spot pairs running down its back, and it feeds on oak leaves along with dozens of other hardwood species.

Because its coloring and hairy body can resemble other species, Maine forestry and health resources routinely include it in side-by-side identification charts. The Maine Forest Service’s browntail moth materials, for instance, feature a chart comparing browntail moth caterpillars with other species commonly mistaken for browntail caterpillars: eastern tent, spongy moth, fall webworm, hickory tussock, and white marked tussock caterpillars. That comparison is a useful reference for anyone trying to sort out which caterpillar is actually on their tree.

Spongy caterpillars established themselves across the Northeast decades ago after first appearing in Massachusetts, and their populations still spread through neighboring states, including established colonies documented among insects in New York. In heavy outbreak years, this species can defoliate large sections of forest, though populations typically crash within a season or two once natural fungal pathogens take hold.

Pro Tip: If a caterpillar’s nest persists through winter and sits at the very tip of a branch rather than in a fork, treat it with caution until you can confirm the species — that placement is a hallmark of browntail moth webs, not the harmless Eastern or forest tent caterpillar.

4. Browntail Caterpillar

The browntail caterpillar (Euproctis chrysorrhoea) is the one species on this list that carries a genuine public health warning. According to the Maine Center for Disease Control and Prevention, the browntail moth is an invasive species found only in Maine and Cape Cod, making this state one of the only places in the country where residents need to worry about it at all.

Identification is fairly straightforward once you know what to look for. The caterpillars reach about 1.5 inches in length and are brown, with a broken white stripe on each side and two red-orange spots on the hind end, and they are active from April to late June. Their winter nests, spun at the tips of branches, look deceptively like clusters of dead leaves that cling on through the cold months.

The real concern is the caterpillar’s tiny hairs, which break off easily and cause a rash similar to poison ivy on contact. The Maine CDC warns that these hairs remain toxic in the environment for up to three years but lose strength over time, so exposure can happen well after the caterpillars themselves are gone. Because of this risk, the following note is worth taking seriously.

Important Note: This article is for educational purposes and is not medical advice. If a browntail moth rash causes severe swelling, breathing trouble, or a reaction that does not improve, contact a healthcare provider or the Maine Forest Service for guidance on safe removal and treatment.

Browntail moth is not a recent arrival. The Maine Forest Service traces its history back over a century, noting that the insect was accidently introduced into Somerville, Massachusetts from Europe in 1897, and by 1913 had spread to all of the New England states and New Brunswick and Nova Scotia. Populations then collapsed for decades, to the point that by the 1960s, browntail moth was limited to Cape Cod and a few islands off the Maine coast in Casco Bay.

The pest reemerged as a statewide problem more recently. Records show that every year since 1994, Maine has noted pockets of high populations of this non-native pest, and in 2015, browntail moth populations entered an outbreak phase, defoliating tens of thousands of acres state-wide annually. As of the 2026 season, though, the trend has been more encouraging: the Bangor Daily News reported that browntail moth caterpillars, the invasive insects carrying rash-causing hairs, are continuing to die off across Maine, with state monitoring sites finding caterpillars dead from viral and fungal pathogens in the spring of that year.

5. Io Moth Caterpillar

The Io moth caterpillar (Automeris io) is a stinging species that belongs to the giant silk moth family and shows up across eastern North America, Maine included. The Missouri Department of Conservation describes mature larvae as yellowish green to bluish green with a red-and-white stripe on the sides, thickly covered with bristly, stinging spines that cause severe irritation in some people.

Young caterpillars look nothing like the adults they’ll become. Early instars start out orange and travel together in tight groups before spreading out and turning green as they mature; as one field guide puts it, when young, larvae are orange and stay in groups; they become more solitary as they mature. This shift in color and behavior can make identification tricky for anyone who only checks a caterpillar once.

Contact with the spines produces an immediate reaction. Research from the LSU AgCenter notes that stings commonly result in an almost immediate painful nettling and itching reaction followed by formation of a localized welt and a reddened flare, with pain usually subsiding within a couple of hours and swelling within six to eight hours. The adult moth, by contrast, is harmless to the touch and known for its dramatic eyespots, with yellow wings on males and reddish brown wings on females, and hindwings that reveal huge eyespots when the moth is prodded.

Gardeners who enjoy raising butterfly caterpillars and other green caterpillar species at home should give the Io moth caterpillar a wide berth rather than handling it directly.

6. Monarch Caterpillar

Few native caterpillars in Maine are as recognizable as the monarch caterpillar (Danaus plexippus), the larval stage of one of North America’s most familiar butterflies. One Maine-focused caterpillar resource calls out the adult monarch as especially memorable, noting that the Monarch is one of our largest butterflies, reaching up to four inches across as a fully grown adult, and is also incredibly recognizable due to its distinctive wing shape and bright orange and black coloring.

The caterpillar itself is banded in black, white, and yellow, and it feeds exclusively on milkweed. That single-host relationship makes milkweed patches in home gardens one of the most reliable ways to attract this species. Anyone curious about how many distinct caterpillars share this kind of specialized diet across North America can explore the broader question of how many types of caterpillars exist in more detail.

Monarchs are also famous for their multi-generational migration, a journey that passes through major flyways documented among insects in Texas before caterpillars ever reach as far north as Maine each summer. Gardeners hoping to support the species should plant native milkweed and avoid pesticides near any patch where eggs or caterpillars are present.

7. Variable Oakleaf Caterpillar

The variable oakleaf caterpillar (Heterocampa manteo) earns its name honestly, since its coloring can range widely from one individual to the next. The Maine Forest Service describes it as a native species that occurs in deciduous forests throughout much of eastern North America, though true outbreaks in Maine are rare events.

In fact, the state has only recorded two major outbreaks of this species. The first, according to Maine Forest Service records, occurred around 1956 when roughly 23,500 acres of northern hardwoods were defoliated in north central Maine. The second began three decades later and grew far larger, with the agency noting that the outbreak began in roughly the same area in 1986 and expanded to include northern hardwood stands across much of central and eastern Maine, peaking in 1988 at roughly 120,000 acres defoliated.

Host preference explains part of why Maine sees fewer outbreaks than states farther south. The Forest Service notes that the variable oakleaf caterpillar can be found on a wide variety of deciduous hosts with oak being preferred throughout most of its range, and of the oaks, white seems to be preferred, which may explain why a lack of white oak in Maine pushes local populations toward beech and sugar maple instead. That same host pattern shows up in oak-rich deciduous forests documented among caterpillar species in Iowa, where white oak is far more abundant.

8. Orangehumped Mapleworm

The orangehumped mapleworm (Symmerista leucitys) rarely acts alone. Maine Forest Service records treat it as a close partner to the variable oakleaf caterpillar during outbreak years, explaining that two species, the variable oakleaf caterpillar and the orangehumped mapleworm, usually make up the major destructive component on beech and sugar maple, aided by the birch sawfly on white and gray birch.

Outbreaks involving this species are rarely simple one-insect events. During the late-1980s defoliation surge, foresters documented an unusually complex mix of feeding insects, noting that outbreaks of this defoliator normally consist of a complex rather than single species, and over 25 different insects were recorded in noticeable numbers from infested stands during the outbreak period from 1988 through 1991. The exact balance between the orangehumped mapleworm and its oakleaf-eating counterpart shifts from year to year, and the ratio of one species to another may change for one reason or another depending on local weather and predator pressure.

Sugar maple stands in other northern hardwood states face similar dual-species pressure, a pattern that shows up in forest health reports from caterpillar species in Wisconsin as well. In Maine, foresters generally monitor rather than actively treat these outbreaks, since populations tend to collapse naturally within a few seasons once parasites and predators catch up.

From harmless tent-builders to the health-hazardous browntail moth, Maine’s caterpillars reflect the state’s mix of native hardwood forest and a long history of accidental insect introductions. Knowing which species is on a tree, and which ones deserve a cautious distance, makes it easier to enjoy the state’s woods and gardens through every stage of the growing season.