10 Remarkable Caterpillars and What They Become

moving GIF showing four stages of caterpillar transformation

Treehugger / Alex Dos Diaz

It's hard not to be captivated by the fluttery, fragile beauty of butterflies and moths. But the caterpillars they start from — with a variety of colors, shapes, markings, and armor — can be equally captivating. What caterpillars all have in common is the incredible metamorphosis they undergo on their journey from egg to butterfly or moth.

Caterpillars represent just one stage of this transformational trek — the larval stage — during which their main purpose is to eat and grow. They grow so much during their brief lives that they typically shed their skin several times, often revamping their appearance from one instar phase to the next. Afterward, butterfly caterpillars molt one final time into a hard chrysalis to begin their magical makeover and moth caterpillars (with a few exceptions) wrap themselves in a silky cocoon.

Whether you love identifying caterpillars in the wild or determining friend from foe in your garden, here's a before-and-after look at some of Mother Nature's most notable species.

1
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Spicebush Swallowtail Butterfly Caterpillar

Bright green spicebush swallowtail caterpillar with yellow and black spots resembling eyes on a green leaf

Ryan Hagerty / Wikimedia Commons / Public Domain

At first glance, these stunning green caterpillars resemble small snakes or tree frogs — a clever disguise designed to ward off predators. Most extraordinary are the false tan eyespots ringed in black. They're not real eyes, but the level of detail in this mimicry is remarkable, including black pupils in the center complete with white highlights that resemble light reflections. If the "evil eye" fails to scare off predators, spicebush swallowtail caterpillars can break out their bright yellow retractable hornlike organs (called osmeteria) located behind their head, which bear a chemical repellent.

These arresting creatures — found throughout the eastern U.S. — hide in folded leaves during the day and venture out in the evening to feed on their foliage of choice, which includes red bay, sassafras, and spicebush. They morph into big, beautiful black-bodied butterflies that sport patches of blue and rows of light spots along their wing edges.

A black, blue, and white spotted spicebush swallowtail butterfly on a purple flowering plant
Spicebush swallowtail butterfly. John Flannery / Flickr / CC BY-ND 2.0
2
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Hickory Horned Devil (Regal Moth) Caterpillar

Green and black hickory horned devil caterpillar with orange/red spikes on a green leaf

Weber / Getty Images

The hickory horned devil looks menacing, but it’s just a harmless, giant caterpillar. One of the largest caterpillars in North America, hickory horned devils can grow to over five inches in length. Everything about them — from their startling turquoise-green bodies arrayed with black spikes to their prickly orange horns — can invoke fear in the uninitiated. Turns out it's all a ruse. These giants, found in eastern U.S. forests, are about as gentle as they come. After feasting on the leaves of hickory, ash, persimmon, sycamore, and walnut trees, they burrow a few inches into the ground in late summer. (They're one of the few moth caterpillars that don't spin cocoons.)

The following summer, they emerge as ravishing orange, gray, and cream-colored regal moths, with an impressive six-inch wingspan.

an orange, yellow, and blue striped regal moth on a human hand
Regal moth. Kadoka1 / Wikimedia Commons / CC BY-SA 3.0
3
of 10

Monarch Butterfly Caterpillar

A yellow, white, and black monarch butterfly caterpillar eating a milkweed

Lynda / Flickr / CC BY 2.0

Come spring, female monarchs begin laying their eggs exclusively on milkweed plants. Once hatched, these strikingly striped orange, black, and white caterpillars devour their nutrient-rich egg shell and begin gorging on milkweed leaves. In the process, they also ingest toxins called cardenolides that don't harm them but are poisonous to predator birds. Within two weeks they've bulked up to 3,000 times their original size.

After this food fest, mature caterpillars attach themselves to a leaf or stem, transform into a chrysalis, and emerge a few days later as the familiar orange-, black-, and white-winged beauties that are so beloved. Monarchs are found throughout North, Central, and South America, Australia, Western Europe, and India. Each fall, monarchs embark on a massive migration to their wintering grounds in Mexico and along the California coastline.

an orange and black monarch butterfly on a bunch of purple flowers
Monarch butterfly. liz west / Wikimedia Commons / CC BY 2.0
4
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Puss (Southern Flannel Moth) Caterpillar

an orange, furry puss caterpillar on a green leaf

Judy Gallagher / Flickr / CC BY 2.0

You might be tempted to pet one of these fluff balls, but that would be a big mistake. The puss caterpillar is one of the most venomous in the U.S. Underneath that toupee-like fur are hidden toxic spines that stick to the skin. Just one touch can unleash excruciating pain far worse than a bee sting. Symptoms may include swelling, headaches, fever, nausea and vomiting, and even shock or respiratory distress. The more mature the caterpillar, the worse the sting.

Puss caterpillars eventually become Southern flannel moths with yellow, orange, and creamy fur on their wings, legs, and bodies.

A yellow and black Southern flannel moth with furry black legs on a red brick wall
Southern flannel moth. Patrick Coin / Wikimedia Commons / CC BY-SA 2.5
5
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Zebra Longwing Butterfly Caterpillar

A black spiked zebra longwing caterpillar on a green leaf

DeadEyeArrow / Wikimedia Commons / CC BY-SA 3.0

These formidable looking caterpillars feed on the leaves of several species of passion flower (Passiflora). But this dietary preference isn't just about nutrition; it's also about predator protection. Passion flower contains toxic, bitter-tasting psychoactive alkaloids. By munching these plants, zebra longwing caterpillars become foul-tasting and toxic, too — an idea that's visually reinforced via their black spots and long black spines.

These imposing creatures are common throughout Central America, Mexico, Florida, and Texas and eventually transform into alluring butterflies known for their long, narrow wings adorned with black and pale yellow stripes.

A brown and yellow striped zebra longwing butterfly on a white daisy plant
Zebra longwing butterfly. Judy Gallagher / Flickr / CC BY 2.0
6
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Saddleback Caterpillar Moth

A green "saddled" saddleback caterpillar with tall red spikes on. a green leaf

Judy Gallagher / Flickr / CC BY 2.0

It's not hard to see how this caterpillar got its name: It's all in the neon green "saddle" on its back, edged in white with a purplish-brown oval spot in the center. Vibrant colors are yet another way Mother Nature sends a warning. These crazy looking critters, found throughout the eastern U.S., Mexico, and Central America, may only be an inch long, but like puss caterpillars, they pack a walloping sting. Beware their four lobes of poisonous spines — two in front and two in back — as well as several smaller stinging protrusions lining their sides.

By comparison, at maturity, the fuzzy, chocolate brown saddleback caterpillar moth is as benign as it looks.

a brown saddleback caterpillar moth on a gray surface
Saddleback caterpillar moth. Andy Reago & Chrissy McClarren / Flickr / CC BY 2.0
7
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Owl Butterfly Caterpillar

a long, brown owl butterfly caterpillar on a green leaf

Harald Süpfle / Wikimedia Commons / CC BY-SA 2.5

Inhabitants of Central and South American rainforests, these slug-like brown caterpillars can reach lengths of up to six inches before transforming into equally impressive butterflies with wingspans of over five inches. Decked out with horns on their heads, forked tails, and a series of black spikes along their spines, these ravenous caterpillars spend most of their time gobbling banana leaves and sugar cane.

Owl butterflies are known for their love of fermented fruit and the fake owl eyes on their wings (complete with a pupil and iris) that are perfectly fashioned to frighten off predatory birds and lizards.

an owl butterfly, with it's distinctive markings that look like owl eyes, on a green stem
Owl butterfly. Pseudopanax / Wikimedia Commons / Public Domain
8
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Cecropia Moth Caterpillar

a green cecropia moth caterpillar with yellow and blue protuberances on a brown stem

Michael Hodge / Wikimedia Commons / CC BY 2.0

These plump green bruisers, found throughout the U.S. and Canada, grow to be over four inches long. As they pack on weight, they turn from black to bright sea green to iridescent bluish green (like the one pictured here). Most impressive, though, are their many blue, orange, and yellow protuberances (tubercles) wielding black spines. They may look scary, but it's all for show.

Cecropia moth caterpillars don't sting or cause harm to humans. Rather, they morph into North America's largest moth and one of its most spectacular species. Adult moths sport reddish-orange bodies and brown wings marked with bands of orange, tan, and white, with white crescent-shaped marks and eye spots.

cecropia moth with a bright red body and gray, red, and white wings on a stem with green plants in the distance
Cecropia moth. Marvin Smith / Wikimedia Commons / CC BY-SA 2.0
9
of 10

Cairns Birdwing Butterfly Caterpillar

A black Cairns birdwing caterpillar with yellow and red spikes on a human hand

Clint Budd / Flickr / CC BY 2.0

These spiky natives of northeastern Australia begin their life on the leaves of a rainforest vine called Aristolochia. Though the vine is poisonous to other caterpillars — and people — Cairns birdwing caterpillars thrive on it. In fact, they store the ingested toxins in the fleshy orange, yellow, and red spines on their backs as a deadly defense against predators.

The butterflies they become (Australia's largest) are equally striking, particularly the vibrant, multi-colored males.

A black, yellow, blue, and green Cairns birdwing butterfly with a red face on a green plant
Cairns birdwing butterfly. Bernard Spragg NZ / Flickr / Public Domain
10
of 10

Hag Moth (Monkey Slug) Caterpillar

A tan colored monkey slug (hag moth) caterpillar with spider-like legs on a green leaf

Greg Dwyer / Wikimedia Commons / CC BY-SA 2.5

At first glance, you might mistake the hag moth caterpillar for a hairy spider. More commonly known as a monkey slug caterpillar, this creature is in a realm all its own. It really doesn't resemble any other caterpillar with its flattened hairy brown body, six pairs of curly, tentacle-like legs (three short and three long), and hairy protuberances sprouting from its head. Those hairs sting, causing irritation and an allergic reaction, particularly in sensitive people.

This bizarre-looking caterpillar transforms into the decidedly less bizarre and innocuous hag moth with its small hairy body and pale tufts on its legs.

A brown hag moth with furry legs on a metal surface
Hag moth.  Donald Hoburn / Wikimedia Commons / CC BY 2.0