Caterpillars in Indiana: Identification and Poisonous Species
Indiana’s landscape runs from the beech-maple forests of the north to the oak-hickory hills of the Hoosier National Forest in the south, and that range of habitats supports one of the more varied caterpillar rosters in the Midwest. Most of what you’ll find is harmless: monarchs feeding on milkweed along rural roadsides, woolly bears crossing bike trails in October, tent caterpillars building silk nests in cherry trees each March. Several species in Indiana sting on contact, and one of them, the puss caterpillar, is the most venomous caterpillar in North America. This guide covers 9 caterpillars in Indiana you’re likely to encounter, with the stinging species clearly marked.
Several caterpillars in Indiana sting on contact. The most dangerous are the puss caterpillar, saddleback caterpillar, and IO moth caterpillar. The puss caterpillar is the most venomous: its soft-looking coat hides hollow spines that cause intense burning, swelling, and sometimes fever. Most Indiana caterpillars, including the woolly bear and monarch, are harmless.
Common Caterpillars in Indiana to Know
Indiana sits at an ecological crossroads between the eastern deciduous forest and the central plains, giving it a wider caterpillar roster than most single-ecosystem Midwest states. The Indiana Department of Natural Resources has documented more than 575 butterfly and moth species statewide, and lepidopterists regularly find species more typical of the Appalachian south alongside those more typical of the Great Lakes north. The state’s geography tells you which species to expect: the beech-maple forests of northern Indiana host forest tent caterpillars and tiger swallowtails; the oak-hickory hills of the Hoosier National Forest in the south see higher saddleback caterpillar and IO moth caterpillar activity; and the agricultural matrix of the central plain sees heavy monarch traffic each August and September along the eastern migration corridor. Caterpillar activity peaks between July and September, with woolly bears crossing roads and paths through October.
1. Monarch Caterpillar (Danaus plexippus)
Bold black, white, and yellow rings circling the whole body, with two pairs of black tentacles at each end. About 2 to 2.5 inches long at full size. Found only on milkweed plants (Asclepias species), which is the fastest way to confirm the ID. If it’s on milkweed, you’re almost certainly looking at a monarch.
Indiana sits on the eastern monarch migration corridor. Milkweed in prairie remnants, roadsides, and old fields across the state sees steady caterpillar traffic from late May through September. The chemicals in milkweed accumulate in the caterpillar and make monarchs toxic to most predators, which is why the bold warning coloring works. Doesn’t sting.
2. Banded Woolly Bear (Pyrrharctia isabella)
Fuzzy with a rusty-brown middle band and black at both ends. About 2 inches long. The hairs don’t sting, though they can mildly irritate sensitive skin. Best known for crossing roads and trails in September and October, searching for somewhere sheltered to overwinter under bark or leaf litter.
Woolly bears survive Indiana winters by producing glycerol before the cold sets in. The glycerol acts as antifreeze in their cells, letting them freeze solid and thaw safely when temperatures rise in spring. The folk tale linking band width to winter severity has no scientific backing. Band width reflects age and food availability during the growing season.
3. Eastern Tent Caterpillar (Malacosoma americanum)
Hairy and blackish with a white stripe down the back, blue spots along the sides, and oval yellow markings. Young caterpillars build communal silk tents in the branch forks of wild cherry, apple, and crabapple trees starting in March and April across Indiana. They leave the tent to feed during the day and return at night.
By May most caterpillars disperse as solitary wanderers, which is when you find them on sidewalks and fence posts. Heavy infestations can strip trees completely, but healthy trees push out new leaves within a few weeks. One of the most recognizable spring caterpillars in Indiana. Doesn’t sting.
4. Forest Tent Caterpillar (Malacosoma disstria)
Despite the name, the forest tent caterpillar doesn’t build a tent. It’s hairy and blue-gray with a row of distinctive white keyhole or footprint-shaped spots running down its back, not a continuous stripe. About 2 inches long at full size. Found on oaks, sweetgum, and other hardwoods throughout Indiana’s forested areas, especially the Hoosier National Forest.
During outbreak years, forest tent caterpillars can defoliate thousands of acres of Indiana hardwood forest by June. Outbreak populations typically collapse within 1 to 2 years as natural parasites catch up. Trees usually flush new foliage after the caterpillars disperse. Doesn’t sting.
5. Eastern Tiger Swallowtail Caterpillar (Papilio glaucus)
Plump and green with two large false eyespots on the thorax: pale yellow-green with a blue center and a dark pupil. Early instars are dark brown with a white saddle mark, mimicking bird droppings. The eyespots on the final instar make it look like a small snake, which is exactly the point.
Found on wild cherry, tulip poplar, ash, and cottonwood throughout Indiana. The caterpillar rests rolled inside a leaf during the day, so look for curled leaves rather than exposed caterpillars. Common statewide, especially in woodland edges, parks, and yards with host trees. Doesn’t sting.
6. Fall Webworm (Hyphantria cunea)
Late-season colonial caterpillar that builds large, ragged silk webs at the branch tips of trees, not in branch forks. The caterpillar varies from pale yellow-green to dark gray, with long white hairs and a row of black spots down the back. About 1 to 1.5 inches long at full size.
Fall webworms feed on over 100 host trees in Indiana, including black cherry, walnut, elm, and apple. Webs appear at branch tips from late July through October, well after eastern tent caterpillars have finished for the year. The hairs don’t sting. Heavy infestations rarely kill established trees.
Stinging Caterpillars in Indiana
Three caterpillars in Indiana deliver a venomous sting on contact. All three cause burning, swelling, and a rash that can last from several hours to several days. The identifying rule that covers two of them: branching, tree-like spines on a caterpillar almost always mean it stings. A fourth species worth knowing, the hickory tussock moth caterpillar (Lophocampa caryae), doesn’t inject venom but its hairs break off and embed in skin, causing a contact rash that can be significant in people with sensitive skin. The full breakdown of spine types and sting mechanisms is in Spiky Caterpillars: How to Identify and Avoid Stings.
7. Puss Caterpillar (Megalopyge opercularis)
Indiana’s most venomous caterpillar, and the most venomous caterpillar in North America. Teardrop-shaped, about 1 to 1.5 inches long, densely covered in grayish-tan to rusty hair that tapers to a tail at the rear. It looks soft. The hair conceals stiff, hollow venomous spines connected directly to venom glands.
Brushing against the puss caterpillar drives those spines into skin and breaks them off. Venom causes intense, immediate burning that can radiate up the arm, followed by swelling, a red grid-like rash matching the spine pattern, and in more severe cases, nausea, fever, and muscle cramps. Puss caterpillars are more common in southern Indiana than the north, found on oaks, elms, and other hardwoods from late summer through October. To treat a sting: press tape firmly over the contact area to lift embedded spines, wash with soap and water, apply an ice pack, and seek medical attention if symptoms spread beyond the sting site or include difficulty breathing.
8. Saddleback Caterpillar (Acharia stimulea)
One of the most visually distinctive caterpillars in Indiana: dark brown at both ends with a bright green midsection, and a brown oval saddle outlined in white sitting squarely in the center. The four knob-like protrusions at the corners of the green section carry the stinging spines. The saddle marking is a warning, and it’s a reliable one.
Touching the spines causes immediate burning, a raised welt, and a rash lasting several hours. Common in Indiana from July through September, found on corn, oaks, cherries, and ornamental garden plants. More frequently encountered than the puss caterpillar in most Indiana counties.
9. IO Moth Caterpillar (Automeris io)
Lime green with a white stripe outlined in reddish-brown along each side. The venomous spines are the same lime green as the body, which makes them easy to miss against leaf surfaces. Touching the spines causes immediate burning, swelling, and hives lasting several hours.
Young IO moth caterpillars are bright orange and cluster in groups on leaves, easier to spot at that stage. By the final instar they’ve shifted to the lime-green form. Found on willows, oaks, maples, and other hardwoods across Indiana from July through September. A plump lime-green caterpillar with bristly tufts on a hardwood leaf deserves caution until you’ve confirmed the ID.
How to Identify Caterpillars in Indiana by Photo
For most caterpillars in Indiana, four clues narrow the ID quickly:
- Color and pattern: solid, striped, banded, or spotted
- Texture: smooth skin, hairy or fuzzy, or spiny
- Host plant: what was the caterpillar on? Monarch on milkweed. Tiger swallowtail on wild cherry or tulip poplar. Fall webworm at branch tips on dozens of host trees. Host plant alone closes most IDs.
- Season: spring tent caterpillars (March through May), summer stingers (July through September), fall woolly bears (September through October)
If those four clues leave you with multiple options, a photo does the rest. Animal Identifier lets you photograph the caterpillar and returns the species name in seconds. After the ID you can ask follow-up questions in the same session: whether it stings, what it’ll turn into, or what host plants to check nearby. It covers insects including caterpillars across Indiana’s forests, prairies, and backyards.
For more on the state caterpillar series, see Caterpillar Identification in Michigan and white fuzzy caterpillar identification for the hickory tussock moth and flannel moth species that also appear in Indiana. For yellow and black species that turn up in Indiana milkweed patches and gardens, black and yellow caterpillars covers the full roster.
Frequently Asked Questions
Are there poisonous caterpillars in Indiana?
Yes. Indiana has several caterpillar species that sting on contact. The puss caterpillar is the most venomous caterpillar in North America and occurs in Indiana, primarily in the southern counties. The saddleback caterpillar and IO moth caterpillar are more widely distributed and also deliver painful stings. The hickory tussock moth caterpillar causes a contact rash from hair contact. If stung, use tape to remove embedded spines, wash with soap and water, apply ice, and seek medical care if symptoms spread or worsen.
What is the most common caterpillar in Indiana?
The banded woolly bear (Pyrrharctia isabella) is likely the most frequently seen species, especially in fall when it crosses roads and paths searching for a winter shelter. Eastern tent caterpillars are the most abundant in spring during outbreak years, with visible colonial tents in wild cherry and crabapple trees across the state.
What caterpillar builds webs in Indiana trees?
Eastern tent caterpillars (Malacosoma americanum) build communal silk tents in branch forks of wild cherry, apple, and crabapple trees starting in March and April. Fall webworms (Hyphantria cunea) build ragged webs at branch tips from July through October. The two are easy to separate by location and season: tent caterpillars appear in branch forks in spring, webworms appear at branch tips in late summer.
When are caterpillars most active in Indiana?
Indiana caterpillar activity runs in two main windows. The first is March through June, when spring-hatching broods feed on fresh foliage: eastern tent caterpillars, forest tent caterpillars, and early butterfly broods. The second runs July through October, when late-season broods fatten before winter, including all three stinging species. Woolly bears cross roads in September and October as they search for overwintering sites under bark and leaf litter.
What does a saddleback caterpillar look like in Indiana?
The saddleback caterpillar is about 1 inch long with a dark brown body at both ends and a vivid green midsection with a brown oval saddle outlined in white in the center. The four corner protrusions carry stinging spines that cause immediate burning and a rash lasting several hours. It’s found on oaks, corn, and garden plants across Indiana from July through September, and is more commonly encountered than the puss caterpillar in most Indiana counties.
If you find a caterpillar in Indiana you can’t place, photograph it and open Animal Identifier. Point the camera, snap a picture, and you’ll have the species and details in seconds. You can ask follow-up questions in the same session, whether you want to know if it stings or what butterfly or moth it becomes. Download it free on iOS or Android and start with 2 identifications a day at no charge.
