Some of the types of caterpillars in Alaska spend most of their lives frozen solid. Woolly bears in the Alaskan Arctic can live for 7 years, thawing each summer just long enough to eat before the cold returns.
Others on this list barely make it into the state, or never arrive at all. Alaska has a short growing season and a thin set of host plants, so each caterpillar here is a case study in timing, survival, or luck.
This article covers six caterpillars that Alaskans, gardeners, and hikers often ask about. They include a famous butterfly that stays south, a garden pest, an Arctic survivor, a clever mimic, a twig look-alike, and an immigrant moth. For a wider look at the group, see this overview of caterpillar types.
1. Monarch Caterpillar
The monarch caterpillar (Danaus plexippus) is easy to recognize. It wears bold bands of yellow, white, and black and has a pair of black filaments at each end. Every one of them depends on milkweed.
That dependence explains why monarchs stay out of Alaska. The monarch does not occur in Alaska because there is no milkweed for its caterpillars and the state lies far north of its migration routes. Anyone who reports a monarch caterpillar in Anchorage or Fairbanks has almost certainly found something else.
The comparison is useful for readers elsewhere in the country. The Minnesota monarch butterfly, for example, is a regular summer breeder on prairie and roadside milkweed, which is why the Upper Midwest matters so much to the species. Neighboring states show the same pattern, as the guide to caterpillars in Wisconsin shows.
Key Insight: According to Butterfly Identification, the only regular migrant butterfly to reach Alaska is the painted lady, and it arrives only in some summers.
2. Imported Cabbageworm
The imported cabbageworm (Pieris rapae) is a velvety green caterpillar with a faint yellow stripe down its back. It is the larval stage of the small white butterfly many people call the cabbage white. The species came from Europe and now follows cabbage crops across North America.
The caterpillar chews broccoli, kale, cabbage, and related plants, leaving ragged holes and green droppings. Its color blends so well with leaf surfaces that gardeners often find the damage before the culprit.
- Check the undersides of leaves, where eggs and small larvae hide.
- Pick caterpillars off by hand in small beds.
- Cover young plants with floating row cover before butterflies start laying eggs.
Important Note: Alaska records for this species are patchy, and the state’s cool summers limit how many generations it can complete. Gardeners who suspect a cabbageworm outbreak can confirm the identification with their local Cooperative Extension office before treating plants.
3. Woolly Bear
The woolly bear is the best-known caterpillar in the far north, and the name covers more than one species. On a sunny August hike near Juneau, the Alaska Department of Fish and Game describes meeting a fat, inch-long, fuzzy caterpillar in black and orange. Woolly bear caterpillars are the final larval stage of the spotted tussock moth (Lophocampa maculata), according to the Alaska Department of Fish and Game.
The banded look appears late. The caterpillar passes through five instars, and the black and orange banded form is the fifth and final one. Earlier stages are small and mostly black, so most hikers walk past them.
The banded woolly bear (Pyrrharctia isabella) also appears on Alaska caterpillar checklists. Its cold tolerance has been measured in the lab. In a study in the Journal of Experimental Biology, caterpillars acclimated for 18 weeks at 5°C survived a week of continuous freezing at -20°C.
The true Arctic specialist is the Arctic woolly bear (Gynaephora groenlandica). It creates a silken shelter near the permafrost and freezes each winter, protected by glycerol that it makes itself. It has even survived an entire winter completely frozen in an ice cube, according to the National Weather Service.
Important Note: Sources disagree on how long the Arctic woolly bear takes to mature. Alaskan field studies point to about 7 years, while the National Weather Service cites at least 14 years for Arctic populations, so treat any single number as a range.
Woolly bears are generally harmless, but their bristly hairs can irritate sensitive skin. Wash your hands after handling one, and check the guide to poisonous caterpillars for species that need real caution.
4. Viceroy Caterpillar
The viceroy caterpillar (Limenitis archippus) is a master of disguise. It is mottled brown and cream with a saddle-like patch of pale color, and it sits on leaves looking much like a bird dropping. Two fleshy bristled knobs behind its head add to the odd outline.
Its host plants are willows and poplars, which grow across Alaska’s Interior and boreal forests. That gives the viceroy a food supply that the monarch lacks, and the butterfly’s range reaches north through western Canada. The neighboring guide to caterpillars in Canada covers the same boreal belt.
The adult viceroy looks so much like a monarch that many people confuse the two, though it is smaller and has a black line across its hindwings. Among butterflies native to Minnesota, the viceroy is a common wetland and willow-thicket species. That makes the Upper Midwest a good place to compare the two look-alikes side by side.
5. Large Maple Spanworm
The large maple spanworm (Prochoerodes lineola) is an inchworm, or looper. It moves by pulling its rear end up to its front legs, arching its body, and then stretching forward. When it stops, it freezes at an angle to a twig and looks like part of the branch.
Spanworm caterpillars eat the leaves of deciduous trees such as maple, birch, and alder. Alaska has few maples, so birch and other broadleaf trees are more likely hosts in the state. The adult is a pale, reddish-tan moth with a diagonal line across each wing.
Records for this species in Alaska are thin, and it is more familiar in the eastern United States. Anyone searching Alaskan birch for it should look for a twig that moves. Close relatives, such as other geometer moths, are far more commonly reported.
6. Large Yellow Underwing
The large yellow underwing (Noctua pronuba) is a European moth that has spread across North America. Its caterpillar is stout and smooth, usually green or brown, with a pale stripe and a row of dark dashes along each side. It hides in soil and plant litter by day and feeds at night.
The caterpillar eats grasses and low plants, and it can chew garden seedlings down to the ground. Gardeners usually notice it when young plants vanish overnight and cutworm-like curled larvae turn up in the soil.
Alaska watches for introduced caterpillars closely. The USDA Forest Service Alaska Region reports that western tent caterpillars were accidentally introduced into Anchorage in 1988 and 2003 on nursery stock and since eradicated, as of its 2025 status page. The same shipping routes can carry other species, including moths like the underwing.
| Caterpillar | Main Food Plants | Appearance | Alaska Status |
|---|---|---|---|
| Monarch | Milkweed | Yellow, white, and black bands | Does not occur |
| Imported Cabbageworm | Cabbage-family crops | Velvety green with a faint yellow stripe | Garden pest, records patchy |
| Woolly Bear | Low plants, willow, herbs | Fuzzy, black and orange when mature | Present, including Juneau and the Arctic |
| Viceroy | Willow and poplar | Mottled brown and cream, bird-dropping look | Boreal and Interior forests |
| Large Maple Spanworm | Maple, birch, other broadleaf trees | Twig-like looper | Few records |
| Large Yellow Underwing | Grasses and low plants | Green or brown, striped, nocturnal | Introduced species |
Together, these six caterpillars show how differently insects handle Alaska’s extremes. The woolly bear freezes, the viceroy hides in plain sight, the spanworm becomes a twig, and the monarch stays south where its food plant grows. The cabbageworm and underwing arrived with people.
To keep exploring, the guide on how many types of caterpillars exist puts these six in context. In summer, the best way to learn Alaska’s caterpillars is slow walking along willow and birch edges, where most of them feed.