8 Types of Caterpillars in Missouri: A Backyard Field Guide
September 8, 2026
Walk through a Missouri garden in midsummer and there’s a good chance something is quietly chewing through the leaves above your head. The state is home to a striking range of caterpillars, from a milkweed specialist that ends up on monarch waystation signs to a five-and-a-half-inch giant that looks like it crawled out of a fantasy novel. Learning the common types of caterpillars in Missouri makes it much easier to know which ones to leave alone, which ones belong in a butterfly garden, and which ones simply need a closer look before you decide they’re a problem.
This guide covers eight caterpillars that gardeners, hikers, and curious kids across the Show-Me State are most likely to run into, with practical notes on what they eat, when they show up, and how to tell them apart from look-alikes.
| Caterpillar | Typical Size | Host Plants | Season | Sting or Toxicity Risk |
|---|---|---|---|---|
| Monarch | Up to 2 inches | Milkweed | May–September | Toxic if eaten, safe to touch |
| Parsley Caterpillar (Black Swallowtail) | Up to 2 inches | Parsley, dill, fennel, carrot family | May–October | None (defensive gland only) |
| Hickory Horned Devil | 4–5.5 inches | Hickory, walnut, sumac, persimmon | July–October | Harmless despite spikes |
| Fall Webworm | About 1 inch | Many hardwood trees | Summer–fall | Mild hair irritation possible |
| Walnut Caterpillar | Up to 2 inches | Walnut, hickory, pecan | Mid-late summer | Bristles can irritate skin |
| Variable Oakleaf Caterpillar | Up to 1.5 inches | Oak species | Summer–early fall | None known |
| Spotted Datana | Up to 2 inches | Oak, hickory, walnut | Late summer | Bristles can irritate skin |
| Gray Furcula | About 1 inch | Willow, poplar, cottonwood | Summer | None known |
1. Monarch Caterpillar
The monarch caterpillar (Danaus plexippus) is probably the single most recognized larva in Missouri, thanks to its bold yellow, black, and white stripes. The Monarch is one of the most well-recognized caterpillars in Missouri, and its distinctive stripes and tentacles make them look cartoonish. That flashy pattern isn’t just for show.
Monarch caterpillars are toxic to most animals, and at the very least taste bad, a poison that comes from their diet, which is almost entirely made up of milkweed. Toxins from the milkweed plant stay in the caterpillar, producing a bitter taste and poisonous effects. The caterpillars are perfectly safe to observe and handle gently; the toxicity is a defense against predators that try to eat them, not a hazard to curious humans.
Because monarchs feed almost exclusively on milkweed, their presence tracks closely with that plant’s availability. If you have milkweed in your yard or nearby, your chance of finding monarch caterpillars is excellent. Gardeners across the Midwest have leaned into this relationship, planting native milkweed specifically to support the species’ multi-generational migration. If you want to compare how monarchs and other pollinator-friendly caterpillars fare farther north, the caterpillar species found in Wisconsin make for an interesting side-by-side look at the same migratory route.
Pro Tip: If you need to relocate a monarch caterpillar off a sidewalk or driveway, use a leaf or piece of paper rather than bare hands, then set it directly onto a nearby milkweed plant.
2. Parsley Caterpillar (Black Swallowtail)
Anyone who grows herbs in Missouri has probably met the parsley caterpillar at some point. This is the larval stage of the black swallowtail butterfly (Papilio polyxenes), and its appearance changes dramatically as it grows. According to University of Missouri Extension, the young caterpillar resembles a bird dropping, glossy black with a white saddle-like spot on the first and second abdominal segments.
By the final instar, the transformation is complete. By the time the caterpillar is full-grown, it is primarily green, with a thin transverse black line at the anterior portion of each body segment, and a thick transverse black line in the middle of each body segment containing yellow-orange spots. Full-grown caterpillars can be up to 2.0 inches in length.
Most gardeners meet the black swallowtail sooner or later, because parsley, carrot, fennel, and dill are favorite food plants of the caterpillars. Per the Missouri Department of Conservation, larvae feed on virtually any plant in the carrot family, including cultivated dill, fennel, carrots, parsnips, parsley, and celery. If disturbed, the caterpillar has a built-in defense: a stinky, orange, forked gland called an osmeterium pops out to deter predators, and the gland looks like horns or a forked tongue on the back of the caterpillar’s head.
Missouri gardeners sometimes worry about a very similar species. The virtually identical Ozark swallowtail, or Missouri woodland swallowtail, lives in scattered colonies throughout the Ozarks, confined to wooded habitats and glades in that region while black swallowtails are usually seen in more open, sunny habitats. Gardeners farther south dealing with the same herb-eating caterpillars can check the caterpillar species documented in Oklahoma for regional comparison.
3. Hickory Horned Devil (Regal Moth Caterpillar)
Nothing in a Missouri backyard causes quite the same double-take as the hickory horned devil, the larval stage of the regal moth (Citheronia regalis). A Point Lookout, Missouri homeowner learned this firsthand when a construction crew spotted one on his property; as reported by KSDK, it’s the largest caterpillar in Missouri and it might look fierce, but it’s harmless. The caterpillar found in that yard measured 5.5 inches long.
Size is the first thing anyone notices. According to the Missouri Department of Conservation, the species can reach a length up to 5½ inches and is found statewide but well-established in the Ozarks and eastern Missouri, with scattered populations elsewhere. The caterpillars are blue-green with a set of curved, black-tipped orange horns that give the species its dramatic name. They have long, curved horns on the back behind the head that are orange with bluish-black tips.
Important Note: Despite the spiky, dragon-like appearance, MDC and university entomologists agree this caterpillar cannot sting or bite in any harmful way. The horns are soft and used purely for intimidation, not defense through contact.
Diet explains the caterpillar’s other common name. Hickories, including pecan, and their close relatives, black walnut and butternut, top the list of host plants, which is why the caterpillars are called hickory horned devils. Missouri State University biology professor Chris Barnhart has noted that hickory horned devils and regal moths aren’t particularly rare, though not many people see them. That’s largely a matter of timing: adults fly at night, typically between 9:30 p.m. and midnight, and the caterpillars themselves spend most of the day hidden in the canopy. If you’re comparing giant native caterpillars across states, the large caterpillar species found in Florida include several equally oversized relatives in the same silkworm moth family.
4. Fall Webworm Caterpillar
Fall webworms (Hyphantria cunea) are the caterpillars behind the loose, messy silk tents that show up on the outer branches of hardwood trees in late summer and early fall. Unlike the tighter, denser tents built earlier in the season by eastern tent caterpillars, fall webworm nests tend to expand as the colony grows, sometimes enclosing entire branch tips in a gauzy web full of leaf litter and frass.
These caterpillars are pale yellow-green to tan, covered in tufts of long hairs, and feed communally inside their silk shelter for protection from predators and parasitic wasps. They aren’t picky eaters. Fall webworms feed on dozens of hardwood species, including pecan, walnut, oak, and fruit trees, which is why they’re one of the more commonly reported nuisance caterpillars to Missouri extension offices each fall.
It’s easy to confuse fall webworms with the related tent caterpillar and lappet moth family, but timing is the giveaway. Per the Missouri Department of Conservation, the white tents created by tent caterpillars in the crotches of trees are hard to miss in springtime, while fall webworm webs appear later in the season and out at the branch tips rather than in the main crotch of the tree.
Common Mistake: Many homeowners assume any web-covered branch is a sign of tree disease. In most cases, fall webworm damage is cosmetic. Healthy, established trees typically shrug off a season of leaf loss without long-term harm.
5. Walnut Caterpillar
The walnut caterpillar (Datana integerrima) is one of several prominent moth species in Missouri that feed almost exclusively on trees in the walnut and hickory family. Walnut caterpillars are one of many types of prominent moths in the state, and when they are small, they live together in groups; when they mature, they live individually.
Young walnut caterpillars start out reddish-brown and gregarious, clustering on branches in tight groups that can strip a limb of leaves in a matter of days. As they mature and molt toward their final instar, they darken to nearly black and disperse to feed alone, often wandering onto siding, patios, and sidewalks near infested trees, which is usually what triggers a wave of concerned calls to local extension offices in mid to late summer.
Walnut caterpillars belong to the genus Datana, which the Missouri Department of Conservation notes includes 14 species of prominent moths in North America that all look like dried leaves and have fuzzy, dark, rusty heads. A pecan or black walnut tree that suddenly looks half-defoliated in August is a strong clue that a walnut caterpillar colony has been at work. Readers dealing with similar hickory and walnut feeders farther east can check the caterpillar species recorded in Maine for a very different regional mix built around cooler-climate hardwoods.
6. Variable Oakleaf Caterpillar
True to its name, the variable oakleaf caterpillar changes appearance noticeably as it grows, which can make it tricky to identify at a glance. Young larvae are pale green with faint markings, while older caterpillars develop bolder stripes and a more textured, leaf-like camouflage pattern that helps them blend into oak foliage.
This species belongs to the same prominent moth family as the walnut caterpillar and spotted datana, a group the Missouri Department of Conservation describes as having a heavy covering of scales that makes many of them look fuzzy, with some species curling their wings around their abdomens so they resemble a twig. As a strict oak feeder, the variable oakleaf caterpillar tends to show up wherever mature oaks dominate the canopy, particularly in the wooded river bottoms and upland forests found throughout much of Missouri.
Populations can fluctuate significantly from year to year depending on weather, parasitism rates, and predator numbers. In outbreak years, defoliation can be noticeable on individual oak trees, but Missouri’s oak-hickory forests generally recover without intervention. Readers curious how this pattern plays out in other oak-heavy states can compare notes with the oak-feeding caterpillars found in Tennessee.
7. Spotted Datana
The spotted datana is a close relative of the walnut caterpillar and shares many of its family traits, including gregarious feeding habits when young. This species favors oak, hickory, and walnut trees, and like other members of the genus Datana, it holds a distinctive defensive posture when disturbed, arching both ends of its body upward while staying attached to the leaf or branch.
Coloring on mature spotted datana caterpillars typically runs toward dark, striped patterns with fine hairs along the body, similar in general silhouette to the walnut caterpillar but with subtle differences in stripe width and head coloration that entomologists use to separate the two species. The Missouri Department of Conservation lists the spotted datana among the state’s characteristic prominent moths, alongside the gray furcula, variable oakleaf caterpillar moth, and walnut caterpillar moth.
Because this species and its close relatives are limited to specific host trees, finding one is a reasonably reliable sign that a nearby oak, hickory, or walnut is otherwise healthy enough to support a caterpillar colony. The caterpillars of most species of prominent moths are limited to a single family of woody plants, the walnut and hickory family, for example, or the sumacs, poplars, elms, or oaks. Gardeners in the Great Lakes region working through a similar mix of hardwood-feeding species may find it useful to browse the caterpillar species documented in Iowa, Missouri’s neighbor to the north.
8. Gray Furcula
The gray furcula rounds out Missouri’s prominent moth caterpillars with one of the more unusual body shapes on this list. The name “furcula” refers to the forked, tail-like projections at the rear of the caterpillar’s body, structures that can be raised and waved when the larva feels threatened, adding to its slightly alien profile.
Gray furcula caterpillars feed primarily on willow, poplar, and cottonwood, trees commonly found along Missouri’s rivers, creeks, and lowland wetlands. Their coloring tends toward muted grays and greens that blend well with the bark and leaf litter of these streamside habitats, making them far less conspicuous than showier species like the monarch or hickory horned devil.
Because gray furculas share the prominent moth family with the walnut caterpillar, spotted datana, and variable oakleaf caterpillar, all four species can sometimes be found on overlapping habitat edges where hardwood forest meets riverbank. Prominent moths and noctuid moths, both large families in the same superfamily of moths, look similar and have the same basic body shape, tending to be camouflage grays and tans. This overlap is exactly why careful attention to host plant and body shape matters more than color alone when working through Missouri’s many types of caterpillars.
Identifying caterpillars gets easier with practice, and Missouri’s mix of prairie, wetland, and oak-hickory forest habitat supports a genuinely wide range of species beyond the eight covered here. For a deeper dive into the state’s full caterpillar diversity, the complete list of Missouri caterpillar species covers additional finds gardeners commonly report. Those interested in how caterpillar diversity compares across the country can also explore the broader range of caterpillar types found throughout North America, or check how many caterpillar species exist worldwide for a sense of scale. And since gardens rarely host just one kind of arthropod, a look at the spider species sharing the same Missouri backyards rounds out the picture of who else is living among the milkweed and oak leaves.