P
Species Profile

Puss Caterpillar

Megalopyge opercularis

Soft look, sharp sting.
Brett Hondow/Shutterstock.com
Macro of a Southern flannel moth caterpillar, called a puss caterpillar. It s covered in lkhaki colored hair. It is is rounder on the end in the left frame. The end in the right frame comes to a point. It is on a green leaf with visible veins.

At a Glance

Wild Species
Also Known As Pus caterpillar, Asp caterpillar, Tree asp, Woolly slug, Stinging asp
Diet Folivore
Activity Cathemeral
Lifespan 3 years
Status Not Evaluated
Did You Know?

It's not a separate animal from the moth: the "puss caterpillar" is the larval stage of the southern flannel moth (Megalopyge opercularis).

Scientific Classification

The puss caterpillar is the fuzzy larval stage of the southern flannel moth (Megalopyge opercularis). Despite its soft appearance, it has venomous spines hidden beneath the hairlike setae and can cause painful stings in humans.

Kingdom
Animalia
Phylum
Arthropoda
Class
Insecta
Order
Lepidoptera
Family
Megalopygidae
Genus
Megalopyge
Species
Megalopyge opercularis

Distinguishing Features

  • Dense, plush-looking coat of hairlike setae that obscures the body
  • Teardrop/oval shape, often with a tail-like tuft at one end
  • Color variable (gray to tan/orange-brown), but consistently ‘furred’ appearance
  • Venomous spines concealed under the fur; sting can be severe

Physical Measurements

Length
1 in (1 in – 2 in)
Venomous

Appearance

Primary Colors
Secondary Colors
Skin Type Insect larval integument covered by dense hairlike setae; venomous urticating spines concealed beneath the setal coat (defensive).
Distinctive Features
  • Larval body length typically ~25-40 mm when mature.
  • Distinctive teardrop/oval silhouette: broader anterior, tapering posterior.
  • Dense, silky "flannel-like" setae obscure the true body segments and legs.
  • Posterior tail-like tuft of longer setae is a key field mark.
  • Venomous spines hidden under the setae; sting is defensive and triggered by contact/pressure.
  • Often encountered on broadleaf trees and shrubs (e.g., oaks, elms, citrus, ornamentals) in suburban/urban settings.
  • Range: primarily southern/southeastern United States (notably TX-FL and Gulf/Atlantic coastal plain); also recorded into parts of the Mid-Atlantic; occurs in Mexico/Central America in some references.
  • Typically solitary and slow-moving on foliage; may drop or remain still when disturbed before stinging on contact.
  • Overwinters in a tough, hair-lined cocoon (pupal stage) attached to bark/structures; adult is the southern flannel moth (same species).

Did You Know?

It's not a separate animal from the moth: the "puss caterpillar" is the larval stage of the southern flannel moth (Megalopyge opercularis).

Full-grown larvae are typically about 2.5-3.5 cm long (UF/IFAS Extension, EENY-Southern flannel moth).

Eggs hatch in about 6-8 days, and the summer pupal stage can last ~16-20 days; the species may overwinter as a pupa (UF/IFAS Extension, EENY).

Color is highly variable-white/cream, gray, tan, to reddish-brown-yet the teardrop "powder-puff" shape with a tail-like tuft is a key ID clue.

The painful sting comes from hollow, venom-bearing spines hidden beneath the soft setae; the "fur" is a defensive disguise, not just fluff.

Its host range is broad: larvae feed on many common trees and shrubs (often reported on oak, elm, pecan, citrus, and ornamentals), which is why people meet them in yards and parks (UF/IFAS Extension; regional extension bulletins).

The cocoon can retain irritating/venomous hairs-meaning even the pupal casing can be a hazard if handled (commonly noted in extension/medical guidance).

Unique Adaptations

  • Venomous spine system concealed by long setae: a "false soft" appearance that encourages predators (and people) to touch, while the real weaponry is hidden underneath.
  • Teardrop body outline with a trailing tuft: helps break up the outline and may mimic plant debris or a bit of mold/seed fluff-camouflage on bark and leaves.
  • Tough cocoon with an operculum ("lid"): a built-in exit structure for the adult moth that allows emergence without tearing the entire casing (described for Megalopygidae in extension/entomology references).
  • Broad host-plant flexibility: ability to develop on many hardwoods and ornamentals increases survival in mixed forests, edge habitats, and cities.
  • Family-level trait (Megalopygidae): multiple "flannel moth" relatives share the fuzzy-larva + hidden-spines strategy, but differ in color, size, and regional host plants-showing a diverse defensive theme across the group.

Interesting Behaviors

  • Defensive stinging on contact: when pressed against skin, the hidden spines penetrate and deliver venom; this is primarily anti-predator defense rather than a hunting behavior.
  • Solitary, slow-moving leaf-feeder: individuals typically occur alone and spend most of their time grazing leaf surfaces rather than traveling in groups.
  • Drop-and-dangle encounters: larvae are frequently found after falling from trees onto people, patios, or outdoor furniture-an important reason stings occur in urban/suburban settings.
  • Seasonal peaks: in much of the southern U.S., encounters are most common in warmer months; some areas see two noticeable generations/peaks (often spring and fall) depending on climate (extension reporting).
  • Cocooning behavior: the larva spins a tough, oval cocoon in sheltered spots (on bark, leaves, or nearby structures) prior to pupation; adults later emerge through a preformed "lid"/operculum (UF/IFAS Extension).

Cultural Significance

In the southern U.S., the puss caterpillar (Southern flannel moth larva, Megalopyge opercularis) is a well-known health concern. Stings often happen in yards and playgrounds, so schools and parks send seasonal "look-don't-touch" alerts.

Myths & Legends

Name lore: "puss caterpillar" is traditional Southern/U.S. folk naming-puss meaning "cat/kitty," referencing the kitten-like fur; many communities pass down the warning that "the cute fuzzy one is the one that stings."

Regional nickname tradition: in parts of Texas and the Gulf Coast, it's long been called an "asp" (a snake term), a bit of local word-of-mouth folklore reflecting how memorable-and feared-the sting is.

In the South, families and children pass down schoolyard tales about the puss caterpillar (Megalopyge opercularis): a "little fur ball" that drops from trees, a seasonal outdoor warning tied to place and weather.

Etymology as a story: the species name opercularis ("with a little lid") is often explained alongside the cocoon's trapdoor-like emergence opening, a small natural-history narrative used in educational displays and nature walks.

Conservation Status

NE Not Evaluated

Has not yet been evaluated against the criteria.

Population Unknown

Life Cycle

Birth 300 larvas
Lifespan 3 years

Lifespan

In the Wild
2.2–12 years
In Captivity
2.2–6 years

Reproduction

Mating System Data Deficient
Social Structure Solitary
Breeding Pattern Transient
Fertilization Internal Fertilization
Birth Type Internal_fertilization

Adults are solitary; females likely attract males with pheromones and mate via brief copulation with internal fertilization. No pair bond or parental care occurs after mating; females oviposit egg masses on host-plant surfaces and adults disperse.

Behavior & Ecology

Social Solitary Group: 1
Activity Cathemeral
Diet Folivore Oak leaves (Quercus spp.; commonly reported host foliage)
Seasonal Hibernates

Temperament

Non-aggressive, slow-moving larva; defensive sting occurs only with contact (Hossler 2010, JAAD).
Larvae typically reach ~2.5 cm length; remain exposed on foliage between feeding bouts (Heppner, UF/IFAS EENY-443).
Development often reported as egg ~6-8 days, larva ~5-6 weeks, pupa ~2-3 weeks in warm seasons; cocoons can overwinter (Heppner, UF/IFAS EENY-443).
Behavior varies by instar: younger larvae more gregarious in placement, later instars more strictly solitary (Heppner, UF/IFAS EENY-443).

Communication

None known; larvae/adults lack sound-producing organs used for social signaling in this species Heppner, UF/IFAS EENY-443
Chemical communication primarily in adults: female sex-pheromone calling attracts males for mating Heppner, UF/IFAS EENY-443
Contact-mediated deterrence: venomous spines under setae deliver pain on touch, functioning as defensive signaling to predators Hossler 2010, JAAD
Likely uses short-range chemical/tactile cues for host-plant assessment; no evidence of coordinated recruitment Heppner, UF/IFAS EENY-443

Habitat

Biomes:
Temperate Forest Tropical Dry Forest Tropical Rainforest
Terrain:
Coastal Plains Hilly Riverine
Elevation: Up to 4921 ft 3 in

Ecological Role

Polyphagous folivorous herbivore (larval stage) on woody plants; defended prey item (urticating/venomous spines) and common host for parasitoids, linking plant production to higher trophic levels.

Transfers energy from broadleaf trees/shrubs to predators and parasitoids (food-web support) Supports parasitoid biodiversity (as a host for parasitic wasps/flies reported for the species) Contributes to natural pruning/low-level defoliation of host plants during outbreaks (localized herbivory)

Diet Details

Other Foods:
Oak leaves Elm leaves Hackberry leaves Pecan and hickory leaves Citrus leaves Sycamore leaves Willow leaves Leaves of redbud Rose leaves Ivy leaves and ornamental broadleaf shrubs +4

Human Interaction

Domestication Status

Wild

Wild species with no domestication history (not bred or managed as a domesticated animal). Human interaction is mainly incidental encounters (often on ornamental/shade trees) and public-health/extension reporting due to painful stings.

Danger Level

High
  • Immediate intense localized pain after contact (commonly described as severe/burning)
  • Localized erythema (redness), edema (swelling), and possible blistering at the contact site
  • Systemic symptoms reported in medical/extension literature: headache, nausea/vomiting, fever, malaise
  • Lymphadenopathy/lymphangitis (tender nodes or red streaking) can occur
  • Chest pain and significant systemic reactions have been reported (rare but medically important)
  • Eye exposure is a medical emergency
  • Allergic-type reactions are possible; seek urgent care for breathing difficulty, widespread hives, or rapidly progressive swelling

As a Pet

Not Suitable as Pet

Legality: Not usually treated as a pet in most U.S. places, but collecting on protected land or moving Puss caterpillars (Megalopyge opercularis) can be restricted. Because they are venomous, schools often ban them for safety.

Care Level: Expert Only

Purchase Cost: Up to $25
Lifetime Cost: $20 - $150

Economic Value

Uses:
Negative economic impact (medical treatment and lost time from painful stings) Public health/education outreach (identification and sting prevention) Environmental/educational value (native biodiversity; entomology instruction)
Products:
  • No standard commercial products; occasionally maintained for educational display/rearing under strict no-contact handling protocols.

Relationships

Predators 6

Parasitoid wasps Braconidae
Parasitoid wasps Ichneumonidae
Tachinid flies Tachinidae
Insectivorous birds
Insectivorous birds Passeriformes
Insectivorous bat
Insectivorous bat Chiroptera
Anoles
Anoles Dactyloidae

Related Species 5

Black-waved flannel moth Megalopyge crispata Shared Genus
Tropical flannel moth Megalopyge lanata Shared Genus
Crinkled flannel moth Lagoa crispata Shared Family
White flannel moth Norape ovina Shared Family
Io moth
Io moth Automeris io Shared Order

Ecological Equivalents 4

Animals that fill a similar ecological role in their ecosystem

Io moth caterpillar Automeris io Both occur in the southeastern U.S. on hardwood and ornamental trees. Their larvae are spiny and can sting, and both species defend themselves by stinging when touched. Automeris io has exposed spines, while Megalopyge opercularis hides its venomous spines beneath dense fur.
Saddleback caterpillar moth Acharia stimulea Both live on shade trees and garden plants; the larvae have venomous spines that sting. Saddleback larvae (Limacodidae) are smaller and slug-like than Megalopyge opercularis (2.5–3.8 cm) but cause similarly painful skin stings.
Spiny oak slug moth Euclea delphinii Occupies a similar feeding niche (foliage-feeding on hardwoods) and relies on stinging spines for defense. Like M. opercularis, it is frequently encountered on oaks and other broadleaf hosts in the same regions and seasons, leading to similar exposure risk.
Buck moth caterpillar Hemileuca maia Hardwood-feeding, seasonally abundant larvae armed with stinging spines that deter vertebrate predators. Ecologically similar as foliage-feeding larvae in woodland edges and suburban landscapes, although buck moth larvae are more gregarious than typical puss caterpillars.

The puss caterpillar (Megalopyge opercularis), also known as the Southern flannel moth caterpillar, is a venomous caterpillar found in the Southeastern United States and Mexico. It has a dense covering of what appear to be soft, fluffy hairs that resemble fur. However, these hairs, or setae (singularly, seta) are anything but soft! The setae contain venom which causes severe pain, nausea, and difficulty breathing. They should not be touched, and if contact is made with one and a reaction ensues, seek medical attention immediately! They are not aggressive and cannot move swiftly, so they are rather easy to avoid if you know what you’re looking for. keep reading to learn everything you need to know about the puss caterpillar.

Five Furry Facts about Puss Caterpillars

  • The puss caterpillar is the most venomous caterpillar in North America!
  • They are covered in dense hairs that are filled with venom that causes a severe sting if touched. The venom from the sting can cause pain, redness, swelling, and in some cases, an allergic reaction or even anaphylaxis.
  • Puss caterpillars are typically brown or gray and have long, tufted setae, which are bristly hairs, that give them a furry appearance.
  • They are typically found on trees, shrubs, and other plants, and are most active in the late summer and early fall.
  • Puss caterpillars are not aggressive, but they will sting if they feel threatened or if they are touched. To avoid getting stung, it is best to avoid handling or disturbing them.

Scientific Name

The Puss caterpillar shares its scientific name, Megalopyge opercularis, with its adult form, the Southern flannel moth. Megalopyge translates to large bottom, while opercularis is Latin for cover. Popular thought suggests that the name refers to the adult form’s pear shape and the way in which they emerge from the top of their cocoons as if removing a cover or lid.

Appearance

Puss caterpillars, also known as woolly slug caterpillars, are the larvae of the Southern flannel moth. They are covered in dense hairs that can cause severe itching and allergic reactions in humans who come into contact with them. In some cases, the venom from the hairs can even cause serious medical conditions such as chest pain, difficulty breathing, and muscle cramps. The venom is present in the hair follicles, so even if the hairs appear to be brushed off, the venom may remain on the skin and cause a reaction.

Puss caterpillars typically appear fuzzy and have a gray or brown coloration. They may have black-and-white markings on their bodies. Some individuals have an orange or yellow line running the length of their bodies. They are typically about 1 inch long and weigh less than 1 ounce when fully grown. Females tend to be a bit larger than males. Southern flannel moth caterpillars, like most caterpillars, do not have antennae. They have a head, thorax, and multiple segments on their body called abdominal segments.

Macro of a Southern flannel moth caterpillar, called a puss caterpillar. It s covered in lkhaki colored hair. It is is rounder on the end in the left frame. The end in the right frame comes to a point. It is on a green leaf with visible veins.

The puss caterpillar is the most venomous caterpillar in North America!

Behavior

Southern flannel moth caterpillars are slow-moving and typically found on the foliage of trees and shrubs. Puss caterpillars feed on leaves and can cause damage to plants if there are large populations present. They typically rest on the underside of leaves during the day and are active at night. They are not known to be aggressive but are venomous.

Habitat

Puss caterpillars are found throughout the Southeastern United States, from the Carolinas to the Gulf Coast, and Mexico. They are most commonly found in wooded areas, gardens, and residential neighborhoods. Puss caterpillars are particularly common in oak-hickory forests and pine-hardwood forests. They feed on a variety of trees and shrubs such as oak, pecan, apple, and plum. In the wild, they tend to be found on the leaves of trees and shrubs, but when they are in urban or residential areas, they can also be found on bushes and even on the ground, parking in broadleaf groundcover plants.

Diet

Southern flannel moth caterpillars are known to feed on the leaves of a variety of trees and shrubs, including oak, pecan, apple, and plum. They are known to be particularly fond of oak leaves. The caterpillars are also known to feed on other plants such as hickory, elm, and sweetgum. They tend to feed in groups, which can cause significant damage to foliage if there are large populations present. They are known to be herbivores feeding primarily on plants.

However, they are opportunistic eaters that will eat the fruit of agricultural crops. Puss caterpillars cause damage to a variety of crops, including cotton, peanuts, and corn. They feed on the leaves and fruit of these plants, causing defoliation and reducing crop yields. Their feeding can cause cotton bolls to open prematurely, making the cotton inside the bolls unmarketable. They can also injure livestock and humans if contact is made. Control measures, such as the use of pesticides and the introduction of natural predators, can be used to mitigate the damage caused by puss caterpillars.

Predators

Puss caterpillars have a variety of natural predators. These include birds, such as warblers, vireos, and thrushes, as well as mammals like raccoons, opossums, and skunks. They can also be preyed upon by other insects, such as wasps and ants. Paper wasps lay their eggs on or inside the caterpillars. Their larvae then feed on the caterpillars as they develop. Additionally, spiders have been known to feed on puss caterpillars. These predators help to keep puss caterpillar populations in check and prevent overpopulation, which can cause damage to trees and plants.

Threats

Puss caterpillars face several threats. These caterpillars are at risk of exposure to pesticides and herbicides used in agriculture. Climate change and habitat destruction may also affect the population of these venomous caterpillars. Habitat destruction, in the form of deforestation, is the primary threat to the continued existence of the puss caterpillar. Puss caterpillars in agricultural settings will almost certainly be annihilated by some heavy-duty pesticide.

Conversation Status

The conservation status of the Puss caterpillar (Megalopyge opercularis) is not listed. It is not considered a threatened or endangered species and it is not listed under any conservation acts. However, it’s important to note that the conservation status of a species is subject to change as new information becomes available and populations may be affected.

Puss Moth: Lifecycle

The puss caterpillar goes through four stages in its lifecycle: egg, larva (caterpillar), pupa, and adult. The eggs are laid in clusters on the leaves of trees such as oak, hickory, elm, and sweetgum. and shrubs. The eggs hatch in about 7 to 10 days. The larval stage lasts for 4 to 6 weeks, during which time the caterpillar feeds on the leaves of various trees and shrubs, including oak, pecan, and elm. As they grow, they shed their skin several times. This shedding is called an instar. Puss caterpillars are not well-studied, but they are thought to have 5-6 instars or periods of molting.

When they reach full size, they spin cocoons and enter the pupal stage, which lasts from 2 to 3 weeks. The process of metamorphosis that the caterpillar goes through in the cocoon includes several stages: the caterpillar spins a silk cocoon around itself and then molts into a pupa. Inside the pupa, the insect’s body undergoes a complete transformation, during which the wings and other adult structures develop. Finally, the adult moth emerges from the cocoon and is active for about a week, during which time they mate and lay eggs to start the cycle again.

The cocoon of a puss caterpillar is visible center frame. It is attached to a Y shaped tree limb. The limb is horizontal, making the Y of the limb sideways. The cocoon which is mostly shades of gray, is triangular with it'd point facing down. The cocoon is attached to th lower lomb. right below ere it forks into a sideways Y. Against blue isolate.

When they reach full size, puss caterpillars spin cocoons and enter the pupal stage, which lasts from 2 to 3 weeks.

Population

It is difficult to provide an accurate estimate of the population of puss caterpillars. Because they are relatively widespread, and not readily visible during certain developmental stages, their population is difficult to gauge. Their populations can fluctuate from year to year depending on a variety of factors, such as weather conditions and the availability of food.

Wound Care

If you accidentally brush up against a puss caterpillar the first thing you should do is: Don’t panic! Their stings are seldom life-threatening. Then remove any setae using scotch tape. If scotch tape isn’t available, other types of tape will suffice. However, always proceed with caution, following the wishes of the injured party. Placing the tape over the site of the sting lifts out the hairs which contain the venom. Next, wash the area gently, but thoroughly with soap and water. A tincture of comfrey will remove some of the sting, as will baking soda when placed directly on the wound site. If you feel short of breath, dizzy, or have other symptoms that would suggest an allergic reaction, seek medical attention immediately! Otherwise, take it easy and the pain of the sting should dissipate momentarily.

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Sources

  1. ufl.edu / Accessed January 23, 2023
  2. insectidentification.org / Accessed January 23, 2023
  3. wikipedia.org / Accessed January 23, 2023
Kathryn Koehler

About the Author

Kathryn Koehler

Kathryn Koehler is a writer at A-Z-Animals where her focus is on unusual animals, places, and events. Kat has over 20 years of experience as a professional writer and educator. She holds a master's degree from Vanderbilt University. When she is not writing for A-Z-Animals, Kat enjoys puttering in her garden, baking deliciously healthful treats for her family, and playing with her two rescue mutts, Popcorn and Scooter. She resides in Tennessee.

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Puss Caterpillar FAQs (Frequently Asked Questions)

Yes! In fact, the puss caterpillar is thought to be the most venomous caterpillar in North America. The pain of its sting has been compared to that of a heart attack or limb amputation. Let’s have a moment of silence for the individuals who are able to make those comparisons, especially the latter.

Besides pain, The venom from the sting can cause redness, swelling, and in some cases, an allergic reaction or even anaphylaxis.