10 Remarkable Caterpillars and What They Become

The hickory horned devil caterpillar can grow to the size of a hot dog. mcevan [CC BY-SA 3.0]/Wikimedia Commons

It's hard not to be captivated by the fluttery fragile beauty of butterflies and moths. But the caterpillars they start from can be equally captivating.

As you'll see, there are many different types of caterpillars. In fact, the variety of colors, shapes, camouflage markings and predator-repelling armor is truly astounding. They range from gorgeous to garish to downright freaky with horns and stinging spines. What they all have in common, though, is the mind-bending metamorphosis they undergo on their journey from egg to butterfly or moth (both are members of the insect order Lepidoptera).

Caterpillars represent just one stage of this transformational trek — the larval stage. Their main purpose is to eat and eat and eat some more. If you have a garden, you're probably well aware of the damage these greedy grazers can do.

Indeed, caterpillars munch so much and grow so big during their brief lives that they typically shed their skin several times, often totally revamping their appearance from one slough-off to the next (called instars). Afterwards, 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. You can learn more about the shape-shifting process in this smart post by Untamed Science.

Whether you love ID'ing 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.

Spicebush swallowtail butterfly caterpillar (Papilio troilus)

Spicebush swallowtail caterpillar
Spicebush swallowtail caterpillar. Ryan Haggerty [public domain]/Wikimedia Commons

At first glance, these stunning green caterpillars look almost like small snakes or tree frogs — a clever disguise designed to ward off predators. Most extraordinary are the false tan eyespots ringed in black. No 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" treatment fails to scare off predators, spicebush swallowtail caterpillars pull out the really big guns: They rear up and whip out 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 (pictured below) that sport patches of blue and rows of light spots along their wing edges.

Spicebush swallowtail butterfly
Spicebush swallowtail butterfly. John Flannery [CC BY-ND 2.0]/Flickr

Hickory horned devil (regal moth) caterpillar (Citheronia regalis)

hickory horned devil
Hickory horned devil (regal moth) caterpillar. Bob Warrick [CC BY-SA 4.0]/Wikimedia Commons

Yikes! These monsters can grow up to 6 inches long (about the size of a hot dog). Everything about them — from their startling turquoise-green bodies arrayed with black spikes to their prickly orange horns — screams, "Be afraid ... be very afraid!" Even chickens, which rarely turn down caterpillar chow, are known to flee when they see one of these bad boys crawling by.

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 (below), one of North America's largest with an impressive 6-inch wingspan.

Regal moth
Regal moth. Kadoka1 [CC BY-SA 3.0]/Wikimedia Commons

Monarch butterfly caterpillar (Danaus plexippus)

monarch butterfly caterpillar
Monarch butterfly caterpillar. Lynda [CC BY 2.0]/Flickr

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 so many of us love. Monarchs are found throughout North, Central and South America, as well as Australia, Western Europe and even India.

monarch butterfly
Monarch butterfly. liz west from Boxborough, MA [CC BY 2.0]/Wikimedia Commons

Puss (southern flannel moth) caterpillar (Megalopyge opercularis)

puss caterpillar
Puss caterpillar. Judy Gallagher [CC BY 2.0]/Flickr

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 all that kitty-like hair (some liken it to a toupee) are hidden toxic spines that stick to the skin. Just one touch can unleash excruciating pain far worse than a bee sting and may even send you to the hospital with swelling, headaches, fever, nausea and vomiting. The more mature the caterpillar, the worse the sting.

Puss caterpillars eventually become equally puss-like — though harmless — Southern flannel moths (pictured below) with yellow, orange and creamy fur on their wings, legs and bodies.

southern flannel moth
Southern flannel moth. Patrick Coin [CC BY-SA 2.5]/Wikimedia Commons

Zebra longwing butterfly caterpillar (Heliconius charithonia)

zebra longwing caterpillar
Zebra longwing butterfly caterpillar. DeadEyeArrow [CC BY-SA 3.0]/Wikimedia Commons

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.

zebra longwing butterfly
Zebra longwing butterfly. Judy Gallagher [CC BY 2.0]/Flickr

Saddleback caterpillar (Acharia stimulea)

saddleback caterpillar
Saddleback caterpillar. Judy Gallagher [CC BY 2.0]/Flickr

It's not hard to see how this caterpillar got its name. Notice 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 shouts, "Back off!" 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, the resulting fuzzy, chocolate brown saddleback caterpillar moth is as benign as it looks.

saddleback caterpillar moth
Saddleback caterpillar moth. Andy Reago & Chrissy McClarren [CC BY 2.0]/Flickr

Owl butterfly caterpillar (Caligo eurilochus)

owl butterfly caterpillar
Owl butterfly caterpillar. Harald Süpfle [CC BY-SA 2.5]/Wikimedia Commons

Denizens of Central and South American rainforests, these slug-like brown caterpillars can reach 6 inches long before transforming into equally impressive butterflies with wingspans nearly 8 inches across. 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 the largest in the Americas, 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.

owl butterfly
Owl butterfly. Swallowtail Garden Seeds [public domain]/Wikimedia Commons

Cecropia moth caterpillar (Hyalophora cecropia)

cecropia moth caterpillar
Cecropia moth caterpillar. Michael Hodge [CC BY 2.0]/Wikimedia Commons

These plump green bruisers, found throughout the U.S. and Canada, grow to be over 4 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 nasty, but it's all just for show.

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

cecropia moth
Cecropia moth. Marvin Smith [CC BY-SA 2.0]/Wikimedia Commons

Cairns birdwing butterfly caterpillar (Ornithoptera euphorion)

Cairns birdwing caterpillar
Cairns birdwing butterfly caterpillar. Clint Budd [CC BY 2.0]/Flickr

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 (below).

Cairns birdwing butterfly
Cairns birdwing butterfly. Bernard Spragg. NZ [public domain]/Flickr

Hag moth (monkey slug) caterpillar (Phobetron pithecium)

monkey slug (hag moth) caterpillar
Monkey slug (hag moth) caterpillar. Greg Dwyer [CC BY-SA 2.5]/Wikimedia Commons

At first glance, you might mistake the hag moth caterpillar for some kind of hairy spider or octopus-like sea creature. But this head-scratcher, more commonly called a monkey slug caterpillar, 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 caterpillar transforms into the decidedly less bizarre and innocuous hag moth with its small hairy body and pale tufts on its legs.

hag moth
Hag moth. Andy Reago & Chrissy McClarren [CC BY 2.0]/Wikimedia Commons