Caterpillars in Texas: 9 Species and Which Ones Sting

Texas gets a public health advisory every spring. Texas A&M AgriLife Extension issues warnings about “asp season” — their name for the puss caterpillar, which is more abundant in Texas than anywhere else in the country. The state records more than 161 caterpillar species: monarchs on highway milkweed patches, gulf fritillaries cycling through Gulf Coast gardens year-round, and the buck moth caterpillar tied to live oak woodlands across the eastern half of the state. Identifying caterpillars in Texas comes down to three quick checks: body covering (fuzzy, spiny, or smooth), color pattern, and what plant it’s on. This guide covers nine species you’re most likely to encounter, starting with the ones that sting.

Texas has more than 161 caterpillar species. The most important to recognize is the puss caterpillar (asp), which is more abundant here than anywhere else in the US. Other stinging species include the saddleback caterpillar, Io moth caterpillar, and buck moth caterpillar. Body covering, color pattern, and host plant are the three fastest identification clues.

How to Identify Caterpillars in Texas

Texas spans roughly 270,000 square miles across four major ecoregions, from the Piney Woods of East Texas to the Chihuahuan Desert in the west. That range means caterpillar diversity here is far broader than in a single-climate state. Body covering cuts the list fastest: smooth, fuzzy, or spiny each point to different families. Color pattern narrows it further. Host plant closes most identifications, since many caterpillars feed on only a handful of plant species.

Texas records more than 161 documented caterpillar species, from the Piney Woods in the east to the Chihuahuan Desert in the west. Texas A&M AgriLife Extension identifies the puss caterpillar (Megalopyge opercularis), also called the asp, as the most venomous caterpillar in the United States, with its highest population densities running from Dallas southward through the western-central part of the state. Stinging caterpillar season in Texas peaks twice: once in spring (April through May) as larvae emerge with new plant growth, and again in fall (September through October) as a second generation develops. The buck moth caterpillar (Hemileuca maia) is largely absent from most US states but appears specifically in Texas’s live oak woodlands and eastern pine-oak forests, making it a Texas-specific identification priority. Gulf fritillary caterpillars remain active year-round in South Texas, cycling through multiple generations wherever passionflower vines grow. Peak activity for most species statewide runs July through October.

Stinging Caterpillars in Texas

Texas has four stinging caterpillar species that show up regularly across the state. The puss caterpillar is specific enough to Texas that AgriLife Extension publishes a dedicated advisory about it each year.

Puss caterpillar (Megalopyge opercularis), called the asp in Texas, is the one to memorize first. It’s oval and compact, covered in long silky fur ranging from grayish-tan to rust or a mix of both colors. That fur is misleading: hollow venomous spines lie underneath, connected to venom glands. Touching the caterpillar breaks those spines off into skin, delivering a sting that hits within seconds. The pain is sharp and burning, often spreading up the arm within minutes and leaving a grid-pattern welt where the spines made contact. Severe reactions, including headache, nausea, fever, and in rare cases seizures, are documented by Texas Poison Control. Look for asps on live oaks, elms, and hackberry trees from Dallas southward, most commonly from April through May and September through October. Nudge one off a surface with a stick; don’t pick it up.

Saddleback caterpillar (Acharia stimulea) is unmistakable once you’ve seen it. Its back carries a bright green oval patch with a brown spot in the center, exactly like a saddle on a green blanket. Four clusters of fleshy spines protrude from its corners, with smaller spined structures along the sides. It grows to about 1 inch long and feeds on a wide range of plants: corn, palms, ornamental hibiscus, and various garden perennials. Contact causes burning pain and localized swelling that can persist for hours to days. For a closer look at spiny caterpillar species across multiple colors, see the spiky caterpillar identification guide.

Io moth caterpillar (Automeris io) looks decorative but stings. Vivid lime green with a red-and-white stripe running along each side and clusters of branching pale green spines, it’s one of the more striking caterpillars in Texas. Young Io caterpillars feed in groups on the same branch before spreading out individually. They eat oak, corn, willow, and many ornamentals; mature caterpillars reach about 2.5 inches. Skin contact causes immediate irritation similar to a bee sting, with localized redness and swelling lasting an hour or two.

Buck moth caterpillar (Hemileuca maia) is a Texas specialty. Dark brown to black with clusters of branching spines and pale spots along the body, it appears in spring on live oaks across the Edwards Plateau and pine-oak forests of East Texas. It’s one of the first caterpillars of the year in Texas, active as early as February and March when live oaks push new growth. The spines cause a sharp burning sting with localized swelling. Young colonies feed together on the same branch, so you’ll often spot several at once.

Common Non-Stinging Caterpillars in Texas

Most caterpillars you find in Texas are safe to handle. Several of the most striking-looking species won’t cause any skin reaction at all.

Monarch caterpillar (Danaus plexippus) is the benchmark for Texas identifications. Plump and smooth, with bold alternating bands of yellow, black, and white around every segment, it feeds exclusively on milkweed. Texas sits on the central monarch migration corridor, so milkweed along roadsides and in gardens attracts monarchs statewide from spring through fall. A banded yellow-black-white caterpillar on a milkweed plant is almost certainly this species. For comparisons with similar banded species, see the yellow and black caterpillar guide.

Gulf fritillary caterpillar (Agraulis vanillae) is bright orange-red with rows of short, branching black spines. Those spines look alarming but they’re completely soft and don’t sting. The species feeds exclusively on passionflower vines, both native maypop and ornamental varieties common in Texas gardens. In South Texas and along the Gulf Coast, gulf fritillaries cycle through multiple generations year-round. In Central and North Texas, they’re active from spring through fall. On a passionflower vine, a spiny orange-red caterpillar is almost certainly this species.

Black swallowtail caterpillar (Papilio polyxenes) is common in Texas herb gardens. Early instars look like bird droppings: dark brown with a white saddle mark. Final instars are vivid green with yellow-dotted black bands across every segment. It feeds on plants in the carrot family, including parsley, dill, fennel, and wild Queen Anne’s lace, making it a frequent visitor to vegetable gardens. Completely harmless to handle. In Central Texas, it’s active from April through October.

Spicebush swallowtail caterpillar (Papilio troilus) goes through a dramatic change as it grows. Early instars mimic bird droppings. Final instars are vivid green with two large orange-and-black false eyespots near the head, designed to suggest a small snake when tucked inside a rolled leaf. It feeds on spicebush, sassafras, and red bay across eastern Texas. Harmless to touch.

Eastern tiger swallowtail caterpillar (Papilio glaucus) is the large smooth green caterpillar common in Texas yards. As it matures, it develops two prominent false eyespots near the head on a yellow-green background. It feeds on wild cherry, tulip tree, ash, and cottonwood, and mature caterpillars reach 2 inches or more. Often found on ornamental trees in suburban yards. Harmless.

Identifying Texas Caterpillars by Color

Color is the fastest first filter, though host plant and body texture are needed to close most identifications.

Fuzzy or furry body: Puss caterpillar (grayish-tan to rust, highly venomous), woolly bear (rusty brown mid-band between black fuzzy ends, harmless; common in fall across Texas), hickory tussock moth (white with black tufts and long black hair pencils, mildly irritating on contact). Handle any unfamiliar fuzzy caterpillar with gloves. For a detailed look at white fuzzy species, see the white fuzzy caterpillar guide.

Dark body with branching spines: Buck moth caterpillar (dark brown to black, spring, on live oaks, stings), Io moth caterpillar (lime green with branching spines and a red-white stripe, stings). Spines plus a dark body in spring on an oak almost certainly means the buck moth.

Lime green with spines or eyespots: Io moth caterpillar (branching spines, stings), saddleback caterpillar (green saddle on a brown body, stings), spicebush swallowtail (smooth, large false eyespots, harmless), eastern tiger swallowtail (smooth, false eyespots, harmless). Spine presence separates the dangerous from the harmless in this color group.

Yellow, black, and white stripes on milkweed: Monarch caterpillar. The milkweed host plant makes this near-diagnostic.

Orange-red with spines: Gulf fritillary (soft black spines, on passionflower, harmless). On a passionflower vine, this identification is nearly certain.

How Animal Identifier Can Help

When a caterpillar is in front of you and the field marks aren’t adding up, a close-up photo is the fastest next step. Animal Identifier lets you photograph the caterpillar and returns a species ID in seconds, covering moths and butterflies across Texas and beyond.

After the ID, the app’s follow-up chat lets you ask specific questions: whether it stings, what butterfly or moth it becomes, or what plants it eats. The chat stays scoped to animals and won’t go off-topic.

Animal Identifier is free to start, with 2 identifications per day and no account required. Available on iOS and Android. Photograph the caterpillar before you decide whether to touch it.

Frequently Asked Questions

What is the asp caterpillar in Texas?

The asp is the common Texas name for the puss caterpillar (Megalopyge opercularis). Texas A&M AgriLife Extension calls it the most venomous caterpillar in the United States. Its fur hides hollow spines connected to venom glands. Contact drives those spines into skin, causing sharp burning pain that can spread up the arm within minutes. Severe reactions, including headache, nausea, and in rare cases seizures, are documented. Look for it on live oaks, elms, and hackberry trees, particularly from Dallas southward.

What stinging caterpillars are found in Texas?

Texas A&M AgriLife Extension identifies four main stinging caterpillar species: the puss caterpillar (asp), the most venomous in the US, with furry tan to rust-colored fur hiding venom spines; the saddleback caterpillar, with a distinctive green saddle on a brown body and corner spine clusters; the Io moth caterpillar, lime green with branching spines and a red-white stripe; and the buck moth caterpillar, dark and spiny, active in spring on live oaks. All four cause skin reactions ranging from sharp burning pain to localized swelling.

When are caterpillars most active in Texas?

Stinging caterpillar season in Texas peaks twice: April through May as larvae emerge with new plant growth, and September through October during a second generation. Monarchs pass through Texas on their fall migration, with peak caterpillar numbers on milkweed from late August through October. Gulf fritillaries are active nearly year-round along the Gulf Coast and in South Texas. Most species statewide are most abundant July through October.

How do I identify a fuzzy caterpillar in Texas?

Color placement and fur coverage separate the main fuzzy species. The puss caterpillar (asp) is uniformly covered in long, silky grayish-tan to rust-colored fur with no visible structure underneath (highly venomous). The woolly bear has a rusty brown mid-band between black fuzzy ends (harmless). The hickory tussock moth is white with black tufts and two long black hair pencils at each end (mildly irritating). For a closer look at white fuzzy species, see the white fuzzy caterpillar guide.

How do caterpillars in Texas compare to other states?

Texas has a broader caterpillar roster than most states, with 161 documented species spread across four major ecoregions. The puss caterpillar (asp) reaches its highest US densities in central and south Texas, making stinging caterpillar season a bigger public health issue here than in most states. The buck moth caterpillar is largely absent from states west of the Mississippi but is a regular presence in Texas. For regional comparisons, see the caterpillar identification guide for Michigan or the Florida caterpillar guide.