Some caterpillars have evolved defenses that are surprisingly effective at keeping predators away. Instead of relying only on camouflage, they develop hairs, spines, or bristle-like structures that are connected to venom glands. When touched, these features can break the skin and release irritating toxins, causing an immediate sting-like sensation that makes animals—and even humans—quickly back off.
The outward appearance of these caterpillars is often deceiving. Many are clothed in what looks like soft, fuzzy fur or delicate tufts, giving the impression of being harmless or even inviting to touch. In reality, those hairs often conceal sharp, venomous spines. Some species are even brightly colored, signaling to would-be predators that they are dangerous, while others blend into leaves and bark, relying on accidental contact to trigger their defense.
The reaction to a sting can range from mild to severe. For some, it may only cause itching, redness, or slight burning that fades in a few hours. Others, however, can produce intense pain, swelling, blistering, or rashes that linger much longer. Sensitive individuals may also experience headaches, nausea, or other systemic effects, showing just how powerful these small creatures’ chemical defenses can be.
Habitats where these stinging caterpillars are found vary widely. Some thrive in woodlands where they feed on tree leaves, while others prefer gardens, meadows, or shrubby landscapes. They are especially common in warmer climates, but some can also be found in temperate regions, appearing seasonally during the months when foliage is most abundant. Their presence is often first noticed when someone brushes against one accidentally.
Despite their painful defenses, these caterpillars are an important part of the ecosystem. They act as food sources for birds, small mammals, and predatory insects, even if their spines discourage some predators. Additionally, by feeding on a variety of plants, they play a role in maintaining the balance of vegetation and contribute to the diversity of the food web.
Stinging Caterpillars
Saddleback Caterpillar (Acharia stimulea)
This brightly colored caterpillar is instantly recognizable by its green “saddle” marking with a brown center. Its body is covered in venomous spines that can deliver a painful sting when touched. The sting may cause burning, swelling, and even nausea in sensitive individuals.
Io Moth Caterpillar (Automeris io)
The larvae of the Io moth are covered in branched spines connected to venom glands. Their sting causes an intense burning sensation, sometimes followed by swelling and redness. They are found across North America, often on trees and shrubs.
Puss Caterpillar (Megalopyge opercularis)
Sometimes called the “asp,” this is one of the most venomous caterpillars in the U.S. It looks soft and furry, but hidden among its hairs are toxic spines. Contact can cause extreme pain, headaches, and even systemic reactions requiring medical care.
Hag Moth Caterpillar (Phobetron pithecium)
Nicknamed the “monkey slug” because of its odd shape with hairy, arm-like projections, this caterpillar is deceptive in appearance. Its hairs conceal venomous spines that can sting on contact. The sting is painful but usually not dangerous.
Buck Moth Caterpillar (Hemileuca maia)
These caterpillars form large groups and are often found on oak trees. Their bodies are covered with sharp spines connected to venom sacs. A sting produces burning, itching, and sometimes welts that can last several days.
Stinging Rose Caterpillar (Parasa indetermina)
This caterpillar is brightly colored with stripes of red, orange, and yellow, warning predators to stay away. Its hollow spines contain venom that causes a painful sting and localized swelling. They are commonly found on fruit trees and ornamentals.
Spiny Oak Slug Caterpillar (Euclea delphinii)
Though small, this species is covered in colorful, spine-like protrusions. Its venomous spines deliver a painful sting that can cause irritation, redness, and rashes. Its bright coloration acts as a natural warning sign.
White Flannel Moth Caterpillar (Norape ovina)
This caterpillar has tufts of long hairs that hide venomous spines underneath. Touching it can result in painful stings, skin irritation, and itching. They are often found on shade trees and ornamentals in the southern United States.
Flannel Moth Caterpillar (Megalopyge crispata)
A close relative of the puss caterpillar, this fuzzy larva also conceals venomous spines beneath its soft-looking hairs. Contact results in a sharp, burning sting followed by swelling and redness. It often feeds on hardwood trees and shrubs.
Blue-striped Nettle Grub (Parasa lepida)
Found in parts of Asia, this caterpillar is strikingly colored with blue and yellow stripes. Its body is armed with clusters of venomous spines that deliver painful stings. It is known to infest fruit trees, making encounters with people more likely.
Cup Moth Caterpillar (Doratifera vulnerans)
Native to Australia, this caterpillar has rows of venomous spines along its back. When touched, the spines release venom that causes a painful burning sensation, often lasting for hours. It feeds on eucalyptus and other native trees.
Spiny Elm Caterpillar (Nymphalis antiopa)
The larval stage of the mourning cloak butterfly, this caterpillar is black with red spots and branched spines along its body. Contact with these spines can cause irritation, burning, and mild rashes in sensitive individuals.
Tree Asp Caterpillar (Megalopyge opercularis group, regional variation)
This caterpillar closely resembles the puss caterpillar but varies in appearance depending on location. It has dense, silky hairs that hide venomous spines. Its sting can be excruciating and may require medical attention.
Green Striped Slug Caterpillar (Euclea core)
This small, brightly colored caterpillar has a flattened, slug-like body with sharp spines that inject venom on contact. The sting causes burning pain and red welts. Its vivid patterns act as a warning to predators.
Nettletree Caterpillar (Euprosterna elaeasa)
Common in Central and South America, this caterpillar feeds on nettle trees and related plants. Its spines can cause a painful sting, followed by skin irritation that may last for days.
Saddle Slug Caterpillar (Sibine stimulea, related group)
Similar to the saddleback, this species has venomous spines arranged in tufts. Its sting can be sharp and burning, often leaving behind itchy welts. It occurs in wooded areas where its host plants grow.
Crowned Slug Caterpillar (Isa textula)
This small, flat-bodied caterpillar carries spiny protrusions that radiate from its edges like a crown. The venomous spines cause stinging pain followed by itching and redness. It is often found on oak, elm, and other hardwood trees.
Variable Oak Slug Caterpillar (Euclea varia)
A close relative of the spiny oak slug, this caterpillar has colorful markings and sharp, venomous spines. Its sting is painful but short-lived, often leaving behind irritated welts. It prefers oak leaves but can feed on other deciduous trees as well.
Southern Flannel Moth Caterpillar (Megalopyge opercularis, regional form)
Another variation of the infamous puss caterpillar, this fuzzy larva looks harmless but delivers one of the most painful stings of any caterpillar. Reactions include burning, swelling, and even nausea in severe cases.
Automeris belti Caterpillar
Found in Central America, this species has rows of venomous spines along its body. Contact with the spines results in burning pain, redness, and sometimes blistering. Its striking appearance acts as a warning to potential predators.
Automeris io Group (related species in Central/South America)
Several close relatives of the Io moth caterpillar across the Americas also carry branched stinging spines. Their sting produces sharp pain and localized swelling, though symptoms vary in severity depending on sensitivity.
Hairy Oak Slug Caterpillar (Euclea flava)
This caterpillar is covered with colorful spines and tufts that conceal venomous barbs. The sting is sharp and irritating, often leaving a rash-like reaction. It prefers feeding on oak trees, hence its name.
Periphoba arcaei Caterpillar
Native to South America, this caterpillar has dense clusters of long, venomous spines. A sting from this species can be extremely painful, with burning, itching, and swelling that may last several days.
Lonomia obliqua Caterpillar (Giant Silkworm Moth Larva)
One of the most dangerous caterpillars in the world, it carries venom that not only causes pain but also disrupts blood clotting. Contact with multiple spines can lead to serious medical emergencies, including internal bleeding. It is found in parts of South America and requires immediate medical attention if stung.