Maine’s mixed forests, coastal meadows, and backyard gardens support an unusually wide range of caterpillars, and not all of them are safe to pick up. Some species here are famous for the wrong reasons: the browntail moth caterpillar has triggered public health warnings across the state, while others, like the monarch, are beloved visitors that gardeners actively try to attract. Understanding the types of caterpillars in Maine helps homeowners, hikers, and gardeners tell a harmless leaf-eater from one that deserves a wide berth.
This guide walks through 23 species found across the state, covering what each one looks like, what it eats, and whether it poses any risk to people or trees. For a broader look at caterpillar diversity beyond New England, the main caterpillar guide covers species found throughout North America.
1. Eastern Tent Caterpillar
The eastern tent caterpillar (Malacosoma americanum) is one of the first defoliators Mainers notice each spring, thanks to the silky webbed “tents” it spins in the forks of wild cherry and apple tree branches. According to the Maine Forest Service, these caterpillars are present in their webs from late April to June and are covered with brown hairs and a solid whitish line down the back flanked by a row of pale blue spots. The caterpillars disperse from the tent each day to feed, then return to the shelter at night.
Despite their startling numbers in a single tent, eastern tent caterpillars are not considered dangerous to touch. Their fine hairs do not sting, which is why many gardeners tolerate them on fruit trees even as populations fluctuate in cycles that build for several years before crashing. They are easy to confuse with the state’s other major tent-builder, the forest tent caterpillar, covered further below.
2. Spongy Moth Caterpillar
The spongy moth caterpillar (Lymantria dispar dispar) carries a name that changed in 2022, when entomologists retired the previous common name in favor of “spongy moth,” a reference to the sponge-like texture of its egg masses. This invasive European species is covered in long hairs and sports five pairs of blue dots followed by six pairs of red dots running down its back, a pattern that helps separate it from Maine’s native tent caterpillars.
Spongy moth caterpillars feed on a huge range of hardwoods, with oak among their preferred hosts, and outbreak years can leave entire hillsides looking skeletal by midsummer. Maine shares this pest with much of the Northeast; readers comparing regional insect pressure may find the insects found in New York worth a look, since spongy moth populations move along similar corridors.
3. Forest Tent Caterpillar
Unlike its eastern cousin, the forest tent caterpillar (Malacosoma disstria) does not build an enclosed tent at all. Instead, it spins a flat silk mat on a trunk or branch where the colony rests between feeding bouts, a trait entomologists use to separate M. disstria from M. americanum at a glance. The caterpillar’s back carries a row of cream or white keyhole-shaped spots rather than the solid stripe seen on the eastern tent caterpillar.
Forest tent caterpillars favor aspen, oak, birch, and maple, and Maine experiences cyclical outbreaks that can strip large stands of these trees bare for a season or two before predator and disease pressure brings populations back down. Several other northern states track the same insect; the caterpillars found in Wisconsin include this species as well, since forest tent caterpillar outbreaks often track across the broader Great Lakes and Northeast hardwood belt.
| Species | Shelter Type | Primary Hosts | Risk to Humans |
|---|---|---|---|
| Eastern Tent Caterpillar | Tent in branch forks | Wild cherry, apple | Low |
| Spongy Moth Caterpillar | No shelter, free-roaming | Oak, many hardwoods | Low |
| Forest Tent Caterpillar | Flat silk mat | Aspen, oak, birch, maple | Low |
| Browntail Moth Caterpillar | Winter web on leaf | Oak, apple, cherry, rose | High |
4. Browntail Moth Caterpillar
The browntail moth caterpillar (Euproctis chrysorrhoea) is the one species on this list that deserves genuine caution. They may reach 1.5 inches in length and are brown with a broken white stripe on each side and two red spots on the hind end. The primary impact on humans results from contact with poisonous hairs produced by the caterpillars, which are microscopic, toxic hairs that can be airborne or settled on surfaces in browntail moth infested areas.
The Maine Forest Service has found evidence of browntail moth in all 16 Maine counties, and the problem has only grown. Experts have said Maine is experiencing one of the worst browntail moth caterpillar outbreaks in nearly a century. The hairs remain toxic in the environment for up to three years, so exposure risk doesn’t end when the caterpillars pupate.
Pro Tip: A key feature for identifying browntail moth caterpillars is two orange dots on the tail end. If you need to clear a web, use a wet/dry vacuum with a HEPA filter filled with soapy water rather than touching the caterpillars directly.
Direct skin contact or airborne hair exposure causes a rash on exposed skin that tends to be red, bumpy, and itchy, and can cause discomfort for hours to weeks. Anyone managing an infestation on their property should also review the state’s full list of poisonous caterpillars, since browntail moth is far from the only species capable of causing a reaction.
5. Green-Striped Mapleworm
The green-striped mapleworm is the larval stage of the rosy maple moth (Dryocampa rubicunda), one of the most visually striking moths to turn up in Maine as an adult, with pink and yellow wings. The caterpillar itself is pale green with darker green stripes running the length of the body and a pair of short black spines near the head, giving it a faintly horned look.
These caterpillars feed in groups on red, sugar, and silver maple leaves, and a heavy population can defoliate individual branches by late summer even though the damage rarely threatens a tree’s long-term health. Gardeners in other maple-heavy states see the same pest; the insects documented in Ohio include this species feeding on street and yard maples in much the same way.
6. Hickory Tussock Caterpillar
The hickory tussock caterpillar (Lophocampa caryae) stands out with its dense coat of white to pale-gray fuzz, broken up by tufts of black hair scattered down the back and two long black “pencil” hairs projecting from the head and tail. It feeds on hickory, walnut, ash, and several other hardwoods, often stripping individual leaves down to the veins in small groups.
While not considered as hazardous as the browntail moth, the hickory tussock’s hairs can cause a mild skin rash in sensitive individuals, so it’s best observed rather than handled bare-handed. Maine shares this species with much of the eastern hardwood belt; readers can see how its range compares in the caterpillars found in Tennessee, where hickory stands support similar populations.
7. Horned Spanworm
The horned spanworm (Nematocampa resistaria) belongs to the geometer moth family, and like other inchworms, it moves by looping its body forward rather than crawling on a full set of legs. What makes this species unmistakable are the two or more pairs of fleshy, filament-like “horns” projecting from its back, which help it blend in among twigs and bud scales.
This caterpillar feeds on a broad mix of hardwoods and conifers across Maine’s forests, and its camouflage is so effective that most sightings happen by accident, when the caterpillar is disturbed on a branch at eye level. Anyone curious about how inchworms and other geometer-family larvae compare to more common caterpillar body types can browse the broader rundown of different types of insects for context.
8. Io Moth Caterpillar
The io moth caterpillar (Automeris io) is bright green with a thin red and white stripe running along each side, and at first glance it looks almost cute. That impression fades fast once a hand brushes against its back, because the caterpillar is covered in clusters of venomous spines that deliver a sharp, burning sting on contact.
Io moth caterpillars feed on a wide variety of plants, including willow, cherry, and clover, and they tend to go unnoticed until the sting happens. Entomologists in neighboring states track the same caution; the writeup on insects found in Texas notes io moth caterpillars as one of the more commonly reported stinging species outside New England as well.
9. Monarch Caterpillar
The monarch caterpillar (Danaus plexippus) is instantly recognizable by its bold bands of yellow, black, and white, and it feeds exclusively on milkweed plants in the genus Asclepias. That exclusive diet matters: the toxic cardiac glycosides in milkweed sap accumulate in the caterpillar’s tissue, making both the larva and the adult butterfly unpalatable to most predators.
- Egg laid singly on the underside of a milkweed leaf
- Larva hatches and passes through five growth stages, or instars
- Full-grown caterpillar forms a jade-green chrysalis
- Adult butterfly emerges roughly 10 to 14 days later
Pro Tip: Planting native milkweed rather than ornamental varieties gives monarch caterpillars in Maine gardens the food source they need to complete this cycle before fall migration begins.
Maine’s monarch population is part of the larger eastern migratory group that travels toward central Mexico each fall, a journey that passes through many states along the way, including the desert habitats covered in the caterpillars found in Arizona.
10. Painted Lady Caterpillar
The painted lady caterpillar (Vanessa cardui) varies in color from pale green to nearly black, but it almost always shows a yellow stripe running along each side and a body covered in short branching spines. It builds a loose silk shelter on its host leaf, usually thistle, mallow, or a legume, and feeds from within that protective nest.
Painted lady butterflies are among the most widely distributed species on Earth, and their caterpillars show up in Maine gardens in varying numbers depending on the year’s migration patterns from farther south. Gardeners tracking similar seasonal fluctuations elsewhere in the country may want to compare notes with the caterpillars found in Iowa, where painted lady populations can spike dramatically in certain summers.
11. Saddled Prominent Caterpillar
The saddled prominent caterpillar (Heterocampa guttivitta) gets its name from the brown, saddle-shaped marking across the middle of its otherwise green, humped body. In Maine, it favors beech, birch, and maple, and it has a particular habit of feeding on the underside of yellow birch leaves, where it’s less exposed to predators and weather.
Outbreaks of this species can contribute to visible thinning in Maine’s northern hardwood stands during heavy years, though populations tend to cycle rather than stay elevated indefinitely. Forest health comparisons with other Appalachian hardwood regions, such as the species list in caterpillars found in Virginia, show similar beech and birch defoliators at work.
12. Brown Birch Casebearer
The brown birch casebearer is the larval stage of a small introduced moth, Coleophora serratella, and it behaves unlike most other caterpillars on this list. Rather than crawling freely across foliage, the larva builds and carries a small portable case constructed from bits of leaf material, mining into birch leaves from inside that shelter.
During heavier outbreak years, birch canopies affected by this casebearer can take on a scorched, brown appearance by midsummer, even though individual larvae are tiny and easy to overlook. The species has spread well beyond Maine since its introduction from Europe, and it now appears across much of the insect fauna documented in Canada as well.
13. Oakleaf Caterpillar
“Oakleaf caterpillar” is a common name often applied to the pink-striped oakworm (Anisota virginiensis), a stout, pale caterpillar marked with pink to white longitudinal stripes and a pair of short, dark spines near the head. Groups of these caterpillars feed together on oak foliage, often working through a single branch before moving to the next.
Maine’s oak stands can show patchy defoliation from this species in outbreak years, though most trees recover fully once the feeding season ends. Oak-feeding caterpillars are common across much of the Southeast too, and the species list for caterpillars found in Georgia includes several close relatives that feed the same way.
14. Woolly Bear Caterpillar
The woolly bear caterpillar (Pyrrharctia isabella), the larval form of the Isabella tiger moth, is probably the most recognized caterpillar in Maine thanks to its dense black-and-rust banding and its habit of crossing roads and trails in large numbers every fall. It overwinters as a larva and can survive freezing temperatures by producing natural antifreeze compounds in its tissues.
Pro Tip: The folk belief that a wider rusty-brown band predicts a milder winter isn’t supported by entomological research, since band width mostly reflects the caterpillar’s age and diet rather than any seasonal forecast.
Woolly bears are completely harmless to handle, which makes them a favorite for curious kids and classroom nature lessons alike. For readers wondering just how many species share Maine’s woods with this familiar banded caterpillar, the overview on how many types of caterpillars exist puts the diversity in perspective.
15. Imported Cabbageworm
The imported cabbageworm (Pieris rapae) is the velvety green larva of the cabbage white butterfly, marked with a faint yellow stripe down its back that helps it blend almost perfectly with brassica leaves. Introduced from Europe in the 1860s, it has since become one of the most persistent pests in Maine vegetable gardens, targeting cabbage, broccoli, and kale.
Because the caterpillar’s coloring matches its host plant so closely, gardeners often notice the chewed leaf margins before they spot the insect itself. This same pest troubles growers well beyond New England; the vegetable-garden pressures covered for insects found in Texas include the identical species working through brassica crops there.
16. Fall Webworm
The fall webworm (Hyphantria cunea) builds large, loose silk webs at the ends of branches rather than in the branch forks favored by the eastern tent caterpillar, and the two are frequently confused by homeowners. The caterpillar itself is pale yellow-green to gray with a hairy coat and scattered dark spots, and it feeds inside the expanding web through late summer and into fall.
Fall webworm damage looks dramatic, especially on roadside cherry and ash trees, but it’s generally considered a cosmetic issue rather than a serious threat to tree health, since the attack comes late in the growing season when trees have already stored most of their energy. Readers interested in how webbing caterpillars compare across coat colors may want to check the guide on white caterpillars for a broader comparison.
17. Uglynest Caterpillar
The uglynest caterpillar (Archips cerasivorana) earns its blunt common name honestly: it spins a loose, messy tangle of silk webbing around a cluster of leaves, usually on wild cherry or chokecherry, and the resulting nest looks ragged compared to the tidier tents of other species. The caterpillar itself is yellowish-green with a black head and feeds from within that webbed shelter.
Because the nest is so visually distinct from the neat tents of the eastern tent caterpillar, it’s one of the easier species on this list to identify from a distance. Similar leaf-tying moths show up across the border as well, and the species list for caterpillars found in Canada includes several close relatives that build comparable messy nests.
18. White-Marked Tussock Caterpillar
The white-marked tussock caterpillar (Orgyia leucostigma) is one of the more elaborately decorated species in Maine, with a yellow-and-black body, a bright red head, two long black hair tufts projecting forward like antennae, a single tuft pointing backward, and dense brush-like tufts of white or cream hair along its back. The overall look resembles a tiny, ornate toothbrush more than a typical caterpillar.
This species feeds on a wide range of hardwoods and conifers, and while it’s generally not dangerous, its hairs can cause mild skin irritation in people with sensitive skin. It belongs to the same broader tussock moth group covered further below, and anyone comparing regional pest pressure may find the insects found in New York useful, since this species ranges throughout the Northeast.
19. Banded Tussock Caterpillar
The banded tussock caterpillar (Halysidota tessellaris) carries a softer, paler coat than its tussock relatives, ranging from pale yellow to cream, with longer black hair “pencils” projecting from the head and tail and shorter hairs covering the rest of the body. It feeds across a wide range of deciduous trees, including birch, oak, and walnut, and rarely causes noticeable damage even in good numbers.
Like other tussock moth larvae, its hairs can mildly irritate sensitive skin, though it’s generally considered one of the gentler species to encounter in Maine woods. Its range overlaps heavily with the hickory tussock and white-marked tussock caterpillars already described, forming a trio that’s easy to mix up without a close look at color and tuft placement.
20. Spotted Tussock Caterpillar
The spotted tussock caterpillar (Lophocampa maculata) shows a banded pattern of black and orange-yellow tufts that superficially resembles the hickory tussock caterpillar, though the color balance and host preferences differ. This species tends toward willow, alder, and other moisture-loving hardwoods rather than the hickory and walnut favored by its look-alike cousin.
Spotting the difference between Maine’s several tussock species comes down to practice: color ratio, tuft length, and host tree all matter more than overall size. Gardeners wanting a side-by-side reference for fuzzy, banded caterpillars can cross-check against the poisonous caterpillars guide, which groups several tussock-type species together for comparison.
21. American Dagger Caterpillar
The American dagger caterpillar (Acronicta americana) is pale yellow to cream and densely furry, with long black hair “pencils” projecting from the front, middle, and rear of its body, giving it a slightly shaggy, almost comical silhouette. It feeds on a wide variety of deciduous trees and is common enough that most Maine residents encounter it at some point during late summer walks.
As with several other fuzzy caterpillars on this list, the dagger moth’s hairs can trigger skin irritation in people prone to allergic reactions, so a look-but-don’t-touch approach is the safer habit to build. Fuzzy caterpillar identification trips up a lot of first-time foragers and hikers, which is part of why broader regional comparisons, like the species documented for insects kept as pets, often include detailed notes on which hairy larvae are safe to handle and which aren’t.
22. Buck Moth Caterpillar
The buck moth caterpillar (Hemileuca maia) is dark, spiny, and speckled with white, and it carries branched spines capable of delivering a sting more painful than most people expect from an insect this size. Some species have specific food sources—for example, the buck moth caterpillar lives on oak trees, feeding in groups before dispersing to pupate underground.
Because the sting can cause a reaction lasting well beyond the initial contact, it’s one of several Maine species worth teaching kids to recognize and avoid rather than pick up. The precautions that apply to browntail moth exposure, including covering skin during yard work and avoiding bare-handed contact, apply here too.
23. Luna Moth Caterpillar
The luna moth caterpillar (Actias luna) is a large, plump, lime-green larva with faint reddish spots along its sides and short fleshy spines scattered across its segments. It feeds on birch, hickory, and other hardwoods common across Maine, growing steadily through several instars before spinning a papery cocoon on the ground among fallen leaves.
The adult that eventually emerges is one of North America’s most recognizable silk moths, with pale green wings that can span roughly four inches and long trailing tails on the hindwings. Because adult luna moths live only about a week and don’t feed at all, the caterpillar stage is really where this species does all of its growing, making a lucky caterpillar sighting in Maine’s hardwood forests a genuine treat for anyone interested in insect life cycles more broadly.
Maine’s caterpillar diversity ranges from garden regulars like the imported cabbageworm to genuine health hazards like the browntail moth, and knowing which is which matters more in this state than in many others given the scale of the browntail outbreak. Most species here are harmless to observe up close, but a simple rule holds up well across the board: admire the fuzzy, spiny, or brightly marked ones from a short distance rather than picking them up barehanded. For readers who want to keep exploring Maine’s wildlife beyond caterpillars, the guide to snakes found in Maine covers another group of misunderstood backyard residents worth getting to know.