Poisonous Caterpillars

Caterpillars are immature stages of moths and butterflies that often have spines and barbed hooks. With most species, these are for show and are quite harmless, but some of these are poisonous caterpillars and should be left alone.

While caterpillars can be a nuisance to gardens, eating your beloved plants, you shouldn’t go around picking up these little creatures without knowing whether they are safe to be handled or not. More frustratingly, sometimes you might not even be able to see them because they are so good at camouflaging themselves in their environment.

So, how do you know which species are poisonous are which are not? How dangerous are they? Below we will be exploring everything there is to know about poisonous caterpillars, so you can be safe. Keep reading on to find out more.

How do caterpillars become poisonous?

Some caterpillars feed on poisonous plants like milkweed, and store their poison inside. Others, however, have hollow quill-like hairs, connected to poison sacs. When these hairs are touched, they pierce the skin releasing poison. Reactions can range from a mild itching to the more severe pain, swelling, blistering, dermatitis, and even intestinal disturbances.

The older the caterpillar, the more potent its sting will be, with the most powerful right before it pupates.

How can I tell if a caterpillar is poisonous?

There are lots of different caterpillars out there in the world, so it can be difficult to tell which ones are poisonous. They’re not all poisonous, are they?

The answer is no. However, it’s not always easy to know which are and which aren’t dangerous. The general rule is, caterpillars that are brightly colored, have spines or hairs are probably venomous and should not be touched.

The safest thing to do is leave the caterpillar alone until you can identify it and know if it is poisonous or not. Use our list below to see whether the caterpillar is dangerous or not.

What is the difference between a venomous and a poisonous caterpillar?

There are differences between a venomous and poisonous caterpillar. A poisonous caterpillar will harm you if you touch, breathe or consume it due to the toxic substance it carries. On the other hand, a venomous caterpillar injects a toxin or poison through a sting.

Where do poisonous caterpillars live?

Poisonous caterpillars can live all over the world. There are even some living in the United States!

Dangerous Caterpillar Species

As we have established above, there is a difference between venomous and poisonous caterpillars. In the following list of caterpillars, we have separated the two kinds so you can learn more about them in detail.

Saddleback Caterpillar

Order: Lepidoptera
Family: Limacodidae
Genus: Acharia
Species: Acharia stimulea

The saddleback caterpillar is found in the Eastern United States. They have a very unique look, with a small, stocky body that resembles a slug, and two stocky, thick thorns on both the head and tale that are covered with spines.

The primary body color of this poisonous caterpillar is brown, and there is a distinct, bright green marking in the middle of the body, with an oval-shaped reddish mark in the middle that resembles a saddle, which is where it gets its name. Ironically, the moth that this caterpillar eventually turns into is wholly unremarkable and is painted in mottled brown.

The saddleback caterpillar has a potent poison that destroys blood cells. Even a small prick from the poisonous spine can cause asthma, stomachache, and bleeding. When they feel threatened, they will shorten their bodies as much as possible, pushing the thorns forward.

This poisonous caterpillar eats many different types of leaves, including maple, oak, palms, and chestnuts. They hatch from the eggs in spring and late winter (February to March) and take about 5 months to turn into a butterfly.

Monkey Slug Caterpillar or Hag Moth Caterpillar

Order: Lepidoptera
Family: Limacodidae
Genus: Phobetron
Species: Phobetron pithecium

The monkey slug caterpillar, also known as the hag moth caterpillar, is usually found in the Eastern States of the US. It gets its name as a monkey slug caterpillar because it has a short, stocky body with nine pairs of bendable “arms” covered in brown, thin hair. They resemble a dried leaf and blend with their surroundings very well.

These caterpillars are not as poisonous as some. In fact, the poison of the caterpillar hair is mild and causes allergic reactions only in particularly sensitive people.

The monkey slug caterpillar eats many different tree leaves, including oak, elm, apple and cherry. They feed on the underside of the leaves and relies on suction cups to hold on.

They hatch in the spring. The moth that this poisonous caterpillar turns into is called a “hag moth” and is fairly plain looking, with yellowish wings.

Hickory Tussock Caterpillar

Order: Lepidoptera
Family: Erebidae
Genus: Lophocampa
Species: Lophocampa caryae

The hickory tussock caterpillar is native to Southern Ontario, Canada. It is characterized by its black and white coloring, and the long, black hair (containing poison) that covers the front and rear of the body. There are connected black markings in the middle of the back.

A prick from the poisonous hair results in a rash or a swelling similar to poison ivy, however, those that are sensitive to the tussock caterpillar poison may develop severe reactions or feel nauseous.

The hickory tussock caterpillar prefer hickory, walnut, elm and oak leaves. They are mostly seen in from July to September when they actively roam and feed.

Southern Flannel Moth Caterpillar or Puss Caterpillar

Order: Lepidoptera
Family: Megalopygidae
Genus: Megalopyge
Species: Megalopyge opercilaris

The southern flannel moth caterpillar, also known as the puss caterpillar, can be found throughout the southern States, including New Jersey, Arkansas, Florida, and Texas. The name of ‘puss caterpillar’ comes from the fact that they look like tiny Persian cats.

These caterpillars are covered with a dense wooly coat of soft brown hair, and have a slug-like body. Their hairs are orange or bright yellow and resemble fur. They are quite small and thin caterpillars.

The southern flannel moth caterpillar is very dangerous. Sting severity increases with the size of the caterpillar. It can destroy blood cells and those who are touched by one experience burning pain immediately, which is then followed by a rash that looks like an imprint of the spines. People may also have difficulty breathing or start bleeding.

White Flannel Moth Caterpillar

Order: Lepidoptera
Family: Megalopygidae
Genus: Norape
Species: Norape ovina

The white flannel moth caterpillar is related to the southern flannel moth caterpillar. It can be found in Lousiana, Mississippi, Alabama, and Tennessee. Unlike the southern flannel, the white flannel moth has a dark-colored, small body with round, yellow-colored patches. It has a chain made of natural black triangle markings between the bright yellow spots. There are 11 pairs of raised yellow tuffs along this strip bearing hairs.

The white flannel moth caterpillar’s tuffs can cause pain, as well as sometimes allergies and swelling. The head and tail of the caterpillar are orange.

This caterpillar feeds on hackberry, black locust, and redbud trees.

American Dagger Caterpillar

Order: Lepidoptera
Family: Noctuidae
Genus: Acronicta
Species: Acronicta americana

The American dagger caterpillar can be found throughout the whole of Eastern North America. It has a short body and is covered with thin, long green hair. It has thin, long black spines are protruding among the fur-like hair, which are the source of the poison and can give a painful rash.

These caterpillars eat most common forest trees, such as oak, ash, and elm.

Smeared Dagger Moth

Order: Lepidoptera
Family: Noctuidae
Genus: Acronicta
Species: Acronicta oblinita

The smeared dagger moth also lives throughout the whole of Eastern North America. It has a long black body with yellow stripes on the sides. It has bunches of thin, white bristles, which are reddish at the base. The stinging hair that cause severe pain, allergies and swelling.

The smeared dagger moth eats anything from grasses to fruit trees.

Laurelcherry Smoky Moth

Order: Lepidoptera
Family: Zygaenidae
Genus: Neoprocris
Species: Neoprocris floridana

The laurelcherry smoky moth caterpillar lives in Florida and has a short and stocky body that is transparent yellow on the sides, with intermittent black stripes. It is also covered in small, short, yellowish hair that causes the sting and can result in pain, followed by a rash and then blisters.

When threatened, the caterpillar has a small hood in which can hide his head. As its name suggests, it eats off Carolina laurelcherry trees.

Variable Oakleaf Caterpillar

Order: Lepidoptera
Family: Notodontidae
Genus: Lochmaeus
Species: Lochmaeus manteo

The variable oakleaf caterpillar lives in Eastern North America and is named “variable” because it can have different markings on its long, lanky body. The only universal feature is the distinct reddish stripe on the back. Generally, these are long yellowish-beige caterpillars with brown, white, and yellow patterns along their body. The other name “oakleaf” comes from the trees in which it can be found.

There are very few short spines on this species and it is not a stinging caterpillar. However, this caterpillar produces formic acid that can cause a burning sensation similar to stinging and can cause allergies.

Pine Processionary Caterpillar

Order: Lepidoptera
Family: Thaumetopoeidae
Genus: Thaumetopoea
Species: Thaumetopoea pityocampa

The pine processionary caterpillar lives in Southern Europe. They have green bodies with yellow stripes and thin, whitish spines. The venomous spines can cause only a mild allergy in humans, but they are dangerous for pets, especially dogs.

These green caterpillars are social and form colonies that travel together from tree to tree. They feed on pine needles, and each colony settles on a pine branch and makes a nest of silk threads.

Giant Silkworm Moth Caterpillar

Order: Lepidoptera
Family: Saturniidae
Genus: Lonomia
Species: Lonomia obliqua

The giant silkworm moth caterpillar is found in Brazil, particularly in the rainforests. It is one of the least colorful caterpillars and is mostly brown and green, with a striped pattern. It is covered with thin white spines with multiple branches. The endings of the branches are colored black.

This poisonous caterpillar is one of the most dangerous. Its spines can prevent the blood from clotting, causing bleeding and destruction of the body from within.

Despite this horrible reaction from the venom, scientists around the world actively study this venom, because it can help in the treatment of some heart diseases because of its ability to dissolve blood clots.

The giant silkworm moth caterpillar lives in trees and actually help to protect them, because monkeys or other animals will not go near them.

Black-Waved Flannel Moth Caterpillar

Order: Lepidoptera
Family: Megalopygidae
Genus: Megalopyge
Species: Megalopyge crispata

The black-waved flannel moth caterpillar is found across eastern and southern United States, Mexico and eastern Canada.

It has a very similar appearance to the puss moth caterpillar in their final larval stage. However, their sting is nowhere near as bad at the sting of the puss moth caterpillar. They have long white wispy hairs and feed on a variety of different hardwood plants. They are most common in the summer.

Spiny Elm Caterpillar

Order: Lepidoptera
Family: Nymphalidae
Genus: Nymphalis
Species: Nymphalis antiopa

The spiny elm caterpillar is native to Eurasia and North America. This caterpillar turns into the beautiful Mourning Cloak butterfly, which is the state insect of Montana. They can be identified by their black body and row of bright red or orange dots on their back. There is also a jet-black line running up the back that seems to join the dots together.

This poisonous caterpillar can harm from sharp-looking black spines poking out from its body. These are surrounded by smaller white bristles.

White-Marked Tussock Caterpillar

Order: Lepidoptera
Family: Erebidae
Genus: Orgyia
Species: Orgyia leucostygma

The white-marked tussock caterpillar can be found in eastern North America, extending as far west as Texas, California, and Alberta. They are common in late summer and eat tree leaves such as apple, cherry, elm, spruce, rose, and chestnut.

These caterpillars are rightly-colored black, yellow, red, and white. Their body has black and yellow stripes running its length and there are red dots on its body along with 4 white tufts of hair. One of their most unique features are the long hair pencils on each end of their body. At the rear end are prominent red defensive glands with black long tails on either side. At the other end is a dark brown hair pencil pointing at 45 degrees upward.

These poisonous caterpillars do not sting, but their fine hairs can cause irritation and allergic reactions.

Crowned Slug Caterpillar

Order: Lepidoptera
Family: Limacodidae
Genus: Isa
Species: Isa textula

The crowned slug caterpillar is found s found in North America from Minnesota, southern Ontario and Massachusetts to Florida, Texas, and Mississippi.

It looks like a flattened leaf, with its almost spherical green shape. It has stinging spines sticking out from the sides of the body, which are more colorful at the head end and can be a deep red rusty color. These contain the poison. They gradually fade to white or beige at the tail end.

The crowned slug caterpillar is mostly flat, but has a raised ridge in the middle and yellow lines running up the green body. It is also covered in yellow and red spots.

These poisonous caterpillars feed on the leaves of various trees, including oak, cherry, maple, basswood, elm and beech.

Venomous Caterpillars

Buck Moth Caterpillar

Order: Lepidoptera
Family: Saturniidae
Genus: Hemileuca
Species: Hemileuca maia

The buck moth caterpillar is found in most states of Southeastern United States. These caterpillars have a brown to purplish black body with distinct white or yellow spots and their head and limbs are red. There are multiple, thin and branching spines covering the body.

The buck moth caterpillar is one of the largest stinging caterpillars and can measure up to 2.5” (6.5 cm).

These caterpillars eat oak leaves mostly, but will also eat willow, hazelnut, cherry, and rose, as well as grasses. They usually come out around July, and the adult moths fly out in autumn.

The poison of the buck moth caterpillar is carried by the breakable spines on the caterpillar’s body that can cause different reactions, from simple rash or swelling to severe shock.

Spiny Oak Slug Moth Caterpillar

Order: Lepidoptera
Family: Limacodidae
Genus: Euclea
Species: Euclea delphinii

The spiny oak slug moth caterpillar can be found in most eastern states in the US up to the northern areas of Ontario, Canada. It is characterized by a light green, yellow, reddish or orange body, which is covered in thick branching horn-like structures with tiny short spines on them, resembling holly trees.

This caterpillar can cause mild allergies. It is usually seen twice a year in warmer areas and only once a year on spring in colder ones. It feeds on oak leaves exclusively.

Io Moth Caterpillar

Order: Lepidoptera
Family: Saturniidae
Genus: Automeris
Species: Automeris io

The io moth caterpillar are found in Cape Cod and Massachusetts, sometimes in the Gulf States and New England. They begin a reddish brown color with black spines, but, as they grow, change their color to light green with reddish-white stripes. Their spines are arranged in distinct “bouquets” which gives the caterpillar is very unique look.

The spines are mildly poisonous and can cause allergic reactions. This caterpillar eats many different types of plants, such as corn, roses, willow, linden, elm, oak, locust, apple, beech, ash, currant, and clover.

Stinging Rose Caterpillar

Order: Lepidoptera
Family: Limacodidae
Genus: Parasa
Species: Parasa indetermina

The stinging rose caterpillar has a very striking appearance, with a bright yellow or orange body that has a signature purple, black or blue stripe running along the back. There are also reddish lines on either side of the caterpillar’s body. The poison is contained in the stocky yellow horn-like structures with smaller and thinner spines that cover the body.

This caterpillar resides in many states, including Texas, Oklahoma, Florida, New York, Philadelphia, and Illinois. It can be found on rose bushes, maples, oaks, poplars, dogwood, and hickory.

The stinging rose caterpillar usually causes allergic reactions, which can be severe in sensitive people and quite mild for others.

Giant Leopard Moth Caterpillar

Order: Lepidoptera
Family: Erebidae
Genus: Hypercompe
Species: Hypercompe scribonia

The giant leopard moth caterpillar is found through North America from southern Ontario, and southern and eastern United States through New England, Mexico and down to Panama.

It is a fuzzy black caterpillar with red markings, that look like red bands. These are often seen when the large caterpillar rolls up into a ball or when it’s moving. These caterpillars don’t have urticating spines. The pain from the caterpillar sting comes from the stiff spines than can prick the skin.