6 Types of Caterpillars in New Hampshire (and How to Identify Them)

A caterpillar chewing through a milkweed leaf in a Nashua backyard and one wrapped in a silk web on a coastal shrub near the Isles of Shoals are both New Hampshire natives to this story, but they could not be more different in what they mean for the people who find them. Some of the state’s caterpillars are harmless garden visitors on their way to becoming butterflies. Others, like the browntail moth caterpillar, carry toxic hairs that send people to urgent care.

Understanding the types of caterpillars in New Hampshire helps gardeners, hikers, and parents tell a beneficial pollinator-in-progress from a species that needs to be left strictly alone. This guide covers six caterpillars regularly reported across the Granite State, from the beloved monarch to three common vegetable-garden pests that show up in backyard brassica patches every summer.

1. Monarch Caterpillar

The monarch caterpillar (Danaus plexippus) is the caterpillar most New Hampshire gardeners hope to find. It has bold black, white, and yellow bands running the length of its body, with two pairs of thin black filaments near the head and tail. It feeds exclusively on milkweed, and milkweed is essential to the monarch since it is the only plant on which the butterflies lay their eggs and the only food source for the caterpillars.

Common milkweed grows across the state in old fields and along roadsides. According to a Union Leader Forest Journal report on monarch research in southern New Hampshire, common milkweed plants are widespread in New Hampshire in old fields and open roadsides, even turning up in garden beds that are not tended too closely. The same report notes that spotting the tiny horseshoe-shaped feeding holes left by a young caterpillar is often the first clue it is on a leaf nearby. Gardeners sometimes confuse monarch caterpillars with the milkweed tussock caterpillar, a fuzzy, tufted species that also feeds on milkweed. UNH Extension notes that milkweed tussock caterpillars are a native species that evolved alongside the monarch, so both can safely share the same plant. If you want to learn how caterpillars fit into the wider insect world, this overview of different types of insects is a useful starting point.

Pro Tip: If you want monarchs to visit your yard, plant a mix of common milkweed and swamp milkweed. Skip pesticides on and near host plants, since even organic sprays can kill young caterpillars.

Raising Monarchs at Home

Some New Hampshire residents raise monarch eggs or small caterpillars indoors in mesh enclosures to protect them from predators and parasites before releasing the adult butterflies. This hands-on approach has become popular enough that many hobbyists treat caterpillar-rearing as a seasonal extension of keeping insects as pets. Anyone trying this should still keep host plants pesticide-free and change milkweed cuttings daily, since fresh leaves keep caterpillars feeding and growing on schedule.

2. Wooly Bear Caterpillar

The wooly bear caterpillar is the fuzzy, black-and-rust-banded larva of the Isabella tiger moth (Pyrrharctia isabella), and it is arguably the most recognizable caterpillar in New Hampshire. A New Hampshire radio contributor described it directly, noting that the type of caterpillar I see most often is the wooly bear caterpillars, adding that the state’s lush landscapes give the species plenty of places to thrive.

Wooly bears are generalist feeders that eat a wide variety of plants rather than relying on a single host, which is one reason they turn up on sidewalks, trails, and driveways as often as they do in gardens. Their dense, bristly hairs are not toxic, though handling any hairy caterpillar without knowing the species first is a good habit to build, especially given how easily wooly bears can be confused at a glance with more irritating hairy species.

New Hampshire folklore holds that the width of the caterpillar’s rusty middle band predicts the coming winter’s severity. A broader rust-colored band is said to signal a milder season, while a wider black band supposedly points to a harsher one. Wildlife biologists generally treat this as regional folklore rather than a forecasting method, since band width actually reflects the caterpillar’s age and molting stage more than upcoming weather.

Common Mistake: Not every hairy black-and-orange caterpillar is a wooly bear. Some species with irritating hairs share a similar general shape, so it is worth confirming the banded pattern and short, bristly (not long, feathery) hairs before handling one.

3. Browntail Moth Caterpillar

The browntail moth caterpillar (Euproctis chrysorrhoea) is the species New Hampshire residents most need to recognize on sight, and for good reason. In June 2024, state officials confirmed the first appearance of the insect in New Hampshire in decades. According to New Hampshire Public Radio, browntail moth caterpillars, a toxic invasive insect species, have been identified in New Hampshire for the first time in 75 years, according to the state’s Department of Natural and Cultural Resources.

The New Hampshire Division of Forests and Lands reported that the discovery involved winter webs found offshore. As the state’s Department of Natural and Cultural Resources explained, browntail moth caterpillar winter webs have been located and removed at the Isles of Shoals off of the New Hampshire coast, marking the first confirmed incident of the species in the state in 75 years. Forest entomologist Kyle Lombard has been tracking the insect’s spread from Maine for roughly a decade before its arrival on New Hampshire’s coast.

Identification matters here because this species is genuinely hazardous. According to NHBugs.org, the state’s official pest-tracking resource, the hairs of the caterpillar are barbed and contain toxins that create rashes on human skin, and the caterpillar is considered a serious human health risk even though it rarely kills the trees it feeds on. The caterpillars are dark, hairy, roughly an inch and a half long, marked with a broken white stripe down each side and two conspicuous orange-red dots near the tail.

Important Note: Browntail moth hairs cause poison-ivy-like rashes and can trigger breathing problems even through airborne contact, not just direct touch. If you suspect you have found one, do not handle it, and report the sighting through NHBugs.org instead. This information is educational and not a substitute for guidance from a medical professional or licensed pest control expert.

Northern Woodlands notes that browntail moth populations fluctuate year to year, partly because fungal outbreaks and a naturally occurring viral disease can knock caterpillar numbers down sharply in some seasons. The species originally arrived in North America from Europe in the late 1800s, and Maine’s caterpillar populations have dealt with far larger browntail infestations for over a decade, which is part of why New Hampshire foresters were watching the state’s southern border so closely before the 2024 discovery.

4. Imported Cabbageworm

The imported cabbageworm (Pieris rapae) is one of three caterpillar species that UNH Extension identifies as the leading brassica pests in the state. Cornell and UNH researchers describe it plainly: the three most common species are imported cabbageworm, cabbage looper, and diamondback moth, all of which reduce yield and marketability on cabbage, broccoli, cauliflower, kale, and Brussels sprouts.

This caterpillar is velvety green with faint yellow stripes down its back and sides, growing to about an inch long. It is not native to North America; it arrived in shipments of cabbage and related plants and has since become one of the most persistent vegetable-garden pests in New Hampshire. UNH Extension notes that imported cabbageworm overwinters in New Hampshire as a chrysalis attached to brassica debris, which is why cleaning up old plant material at the end of the season helps reduce next year’s population.

Adult imported cabbageworms are the small white butterflies commonly called cabbage whites, easily seen fluttering over vegetable beds in spring and early summer. Gardeners who want a broader sense of how many caterpillar families exist beyond garden pests can check this rundown of how many types of caterpillars there are worldwide.

5. Cabbage Looper

The cabbage looper (Trichoplusia ni) earns its name from its distinctive crawling motion. Lacking a full set of middle legs, it arches its body into a loop with each step, similar to an inchworm. Its coloring is pale green with a faint white stripe running along each side, and it can grow slightly larger than the imported cabbageworm before pupating.

Like the imported cabbageworm, the cabbage looper targets brassica crops across New Hampshire gardens and farms, though UNH Extension’s guidance notes that each species differs in size, feeding habits, and susceptibility to insecticides and predators, so correct identification changes how a grower should respond. Cabbage loopers tend to chew large, irregular holes through leaves rather than skeletonizing them, and they are more likely to bore into the heads of cabbage and broccoli than the imported cabbageworm.

Caterpillar	Typical Coloring	Host Plants	Notable Trait
Monarch	Black, white, and yellow bands	Milkweed only	Harmless pollinator-in-progress
Wooly Bear	Black and rust-brown fuzzy bands	Wide variety of plants	Subject of winter folklore
Browntail Moth	Dark brown, hairy, orange tail dots	Oak and apple trees	Toxic hairs cause rashes
Imported Cabbageworm	Velvety green, faint yellow stripes	Brassica crops	Overwinters as a chrysalis on debris
Cabbage Looper	Pale green, faint white side stripe	Brassica crops	Moves in a looping crawl
Diamondback Moth	Small, pale green, tapered ends	Brassica crops	Wriggles rapidly when disturbed

Gardeners interested in how green coloring shows up across many unrelated caterpillar families can browse this guide to green types of caterpillars for comparison, since color alone rarely confirms a species.

6. Diamondback Moth Caterpillar

The diamondback moth caterpillar (Plutella xylostella) rounds out UNH Extension’s list of the state’s three most common brassica pests. It is the smallest of the three, pale green with a slightly tapered body at both ends, and it moves noticeably fast for a caterpillar when disturbed, often wriggling and dropping from the leaf rather than staying put.

UNH Extension’s crop guidance recommends the same core approach for diamondback moth as for the other brassica pests: effective management requires correct identification, weekly scouting, and integrated pest management. Because diamondback moth caterpillars often feed from within tightly folded leaves or growing points, they can be harder to spot during a quick visual check than the more exposed imported cabbageworm or cabbage looper.

Pro Tip: Check the undersides of brassica leaves weekly through the growing season. Imported cabbageworm, cabbage looper, and diamondback moth caterpillars are all easiest to control while populations are still small, before they reach the point where damage is obvious from a distance.

A fourth species, the cross-striped cabbageworm, occasionally shows up on farms near the Massachusetts border but remains far less common statewide than the diamondback moth. Home gardeners who spot unusual feeding damage on brassicas and cannot match it to these three species should photograph the caterpillar and consult UNH Extension’s Infoline before treating, since misidentifying the pest often leads to picking the wrong control method.

New Hampshire’s caterpillar population ranges from harmless garden visitors to a genuinely toxic invasive species that only recently reestablished itself in the state. Learning to distinguish the monarch’s bold bands, the wooly bear’s folklore-famous fuzz, the browntail moth’s dangerous orange-dotted hairs, and the three lookalike brassica pests gives gardeners and hikers a real advantage each summer. For a wider regional picture, comparing notes with neighboring states like Maine’s caterpillar species or browsing a broader types of caterpillars reference can help fill in the species this guide did not cover.