I Found a Caterpillar -- But What Will It Turn Into?

Identify that cool caterpillar you just found with the help of this guide! Is your caterpillar rare? Does it sting? (see my Stinging Caterpillars lens here) What does it eat? What does it turn into? Here you will find photographs and descriptions of caterpillars of North America. You can also see tons of butterfly photos and descriptions right here.

Caterpillars are the larval stage of Lepidoptera, commonly known as butterflies and moths. They spend their days eating and storing energy for the adult butterfly or moth that they will become. Caterpillars are very well adapted to their natural surroundings, so even though they're all around us, we never see most of them; they are so perfectly disguised, or have such secretive habits, that we walk right by them without ever knowing they're there. But they are! Every once in a while you will come across a caterpillar, and you may wonder what kind of butterfly or moth it will turn into. From six-inch long beasties with curved horns and jagged spikes to the familiar, furry wooly bear, here are some of the most commonly encountered caterpillars of North America.

Some caterpillars can eat enough to damage crops or forests -- the Gypsy Moth caterpillar is a serious pest of oak forests in the northern US. If you grow tomatoes, chances are good you've come across the Tomato Hornworm, a big free monster that can destroy a tomato plant in a week or less. Have a look at this article about identifying and controlling tomato caterpillars!

image:http://morguefile.com/archive/display/165036

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Monarch Butterfly

Monarch Caterpillar Identification

This cool caterpillar is always found on some species of milkweed (Asclepiasspecies). They aren't too hard to spot, with their bright stripes of black, white, and yellow. The milkweed that monarchs feed on is protected by having poisonous sap, and that may give the monarch caterpillar itself some amount of poisonous protection. They are brightly colored and turn into one of the most beautiful and popular of all butterflies: the monarch.

Image: Lisa McDonald / FreeDigitalPhotos.net

Black Swallowtail Caterpillar Identification

This caterpillar looks a lot like the monarch caterpillar (above) -- and that may not be an accident. The monarch is most likely "protected" by the bitter sap of the milkweed plant that it eats, because some of the toxic compounds in the sap become incorporated into the insect's tissues. The black swallowtail caterpillar eats the leaves of carrots and other Umbelliferaespecies, which are not thought to be as toxic as the milkweed, and is likely not protected at all. But sometimes in nature just looking like you're poisonous can be protection enough -- that's the basis of one major form of mimicry. The black swallowtail caterpillar mimics the monarch caterpillar so birds and other predators might leave it alone, putting mistaken identity to good use!

This attractive caterpillar turns into a beautiful, big butterfly known as the black swallowtail.

Image: m_bartosch / FreeDigitalPhotos.net

Black Swallowtail Butterfly

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Sycamore Tussock Moth Caterpillar Identification

This species gets quite common in some parts of the country. You'll most likely find it as it wanders around looking for a place to make a cocoon, so you might want to try keeping the caterpillar in a safe "rearing cage" (here's a link to a lab-quality caterpillar-rearing cage) with a few leaves to see if it'll make a cocoon. The moth is a pretty brown-and-cream moth. This is a species of tiger moth in the Genus Halysidota, which includes many similar species found all over the US.

Sycamore Tussock Moth

Raise Your Caterpillar and See What It Becomes!

You can raise your caterpillar to adulthood -- but you have to keep it safe from predators!

Raise the cool caterpillar you found with the help of one of these cool "bug house" products. If you can keep your caterpillar supplied with fresh leaves from its food plant, and if you can keep it screened from parasites and other predators, then there's a good chance you can have a front-row seat to one of the most amazing natural processes on the planet.

Cecropia Caterpillar Identification

This is a BIG caterpillar -- up to five inches long-- and really cool in appearance, too. The cecropia caterpillar feeds on oak, willow, and maple, among other trees and bushes, and can be found wandering around in late summer as it looks for a place to spin its tough, brown cocoon. This spectacular caterpillar turns into an even more spectacular moth. The ceropia moth, below, is a bat-sized beauty that belongs to the group of "giant silk moths." These are among the largest Lepidoptera in North America.

Cecropia Moth

This Caterpillar Can Kill You.

The larva of Lonomia obliqua

Polyphemus Moth Caterpillar Identification

This is another big caterpillar -- about the size and thickness of your thumb. Polyphemus eat maple, birch, willow and several other trees, but are seldom abundant enough to cause any damage. As big as they are, they are really hard to see among the foliage when they're resting. As with many caterpillars that leave the food plant to spin a cocoon, Polyphemus are sometimes seen wandering around in late summer. This caterpillar spins a tough, brown, oval cocoon that you may find attached to the eaves around your house during the winter.

You can raise this caterpillar easily with the proper cage -- here's a link to a lab-quality caterpillar-rearing cage.

Also visit my blog, which has some great caterpillars sent in by readers: The Caterpillar Identification Blog

Polyphemus Moth

The big eyespots look like an owl and may scare predators away.

Wooly Bear Caterpillar Identification

These little guys are often seen hot-footing it across the road in rural areas of eastern North America. They belong to the family of tiger moths (Arctiidae), which has many attractive and widespread members. Wooly bears are the larva of the Isabella tiger moth, Pyrrharctia isabella, and they feed on a number of common plants of second-growth areas and roadsides. When you see them hustling across the road, they are looking for a good place to spend the winter: this species hibernates under rocks or logs, emerging in the spring to pupate. The moths emerge in early summer.

Pyrrharctia Isabella Moth -- Wooly Bear Tiger Moth

Io Moth Caterpillar Identification

This species, Automeris io, belongs to the group of giant silk moths that also includes the cecropia and polyphemus moths. This is one of the few caterpillars in our area that is protected by irritating spines, which really interested me when I was a kid. I had read all about the animal's "stinging spines" in my trusty Golden Nature Guide. I found one when I was about twelve, and actually brushed the spines against my arm on purpose to see what all the fuss was about. Did it sting? Yes -- kind of like stinging nettles, not intense, but the kind of thing you don't want to repeat. Definitely a good protection for a caterpillar to have!

Io Moth

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Tomato and Tobacco Hornworms

These huge caterpillars can often be found chowing down on your tomato plants, often to the point where the entire plant is eaten. The tobacco and tomato hornworms are very similar, and often eat both plants, as well as sweet potatoes and other crops. They produce similar moths, too, huge brown bombers that are such good fliers they have earned the nickname "hawk moths."

Milkweed Tiger Moth Caterpillar identification

This cool-looking little guy is the larval stage of the tiger moth Euchaetes egle. There are relatively few Lepidoptera species that feed on milkweed, which has poisonous sap that may make the caterpillars themselves poisonous to birds. Like the monarch, milkweed tiger moth caterpillars eat nothing but milkweed and spend all of their time on the plant, living and moving in small groups of up to ten. They're not at all hard to find on the host plant -- their bright coloring is thought to be a kind of warning to predators not to even bother eating them.
For such a showy caterpillar, the adult milkweed tiger moth is pretty plain -- unmarked light gray wings with a spotted abdomen.

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Gypsy Moth Caterpillar Identification

This is the dreaded gypsy moth caterpillar, Lymantria dispar, which can multiply out of control and strip entire oak trees down to the stick. In some cases, entire forests are deprived of their leaves by hordes of these caterpillars. Walking into a forest under siege from gypsy moth caterpillars, you can actually hear the sound of millions of tiny jaws working away, eating every leaf in site.

Gypsy Moth Adults

Forest Tent Caterpillar Identification

This pretty blue and brown caterpillar is often found in large numbers in oak forests. They can be a pest on the level of the dreaded gypsy moth, and like the gypsy moth can defoliate an entire forest in a matter of weeks. They get the name "tent caterpillar" because the group of insects they belong to tend to make silk webs or mats on the branches and trunks of the host trees.
The moth that this caterpillar turns into is a pretty fawn brown color with subtle stripes and a furry body.

Forest Tent Caterpillar Moth

Hickory Horned Devil

When I was a boy, I always hoped to find one of these amazing creatures munching on the leaves of the hickory trees in our neighborhood. I never did, though -- they are not all that common, and live mostly in the south. My bad luck to live in the north! The hickory horned devil is likely the largest, and certainly the fiercest-looking, caterpillar in North America. Full-grown, they are nearly half a foot long, and will rear up and make a clicking sound if you bother them. They're totally harmless, though, like pretty much all caterpillars.
The hickory horned devil turns into the regal moth, a gigantic, beautiful animal that most people will never see in nature.

Regal Moth (Hickory Horned Devil Moth)

Pandorus Sphinx Caterpillar Identification

This bright orange beauty is one form of a somewhat common type of sphinx moth larva -- the other form is green, and while beautiful, is not quite as striking as this one. I've included this caterpillar mainly because I think it's so beautiful -- and also because the kind of moth it produces is also beautiful. This caterpillar in the illustration may be a tropical version of the North American pandorus species -- it's a little hard to tell. But if you find one, you can be sure you've found a truly special insect.

Pandorus Sphinx Moth

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Caterpillar Identification -- Catalpa Sphinx

This species feeds only on catalpa trees, which are very common in the south and becoming mores in the north. These trees have big, pale green leaves and form seed-pods in the fall. They are common ornamental trees and can be found in city and suburb.
The catalpa sphinx can really do a number on an infested tree, but there is also a type of parasitic wasp that does a number on the caterpillars by laying eggs on the worm, which then turn into little wasp larvae that eat the caterpillar from the inside out. This kills the caterpillar, as you might guess!

Caterpillar Identification -- Mourning Cloak

This caterpillar eats elm, and is known in some places as "the spiny elm caterpillar." It is the larval stage of one of the best-known butterflies in the world, the mourning cloak. This beautiful insect occurs in the US and in Europe -- in the UK, it is incredibly rare, and entomologists can spend a lifetime waiting for one to show up (it's known as "the Camberwell Beauty" in England). Up close, the upper side of the mourning cloak is gorgeous. The underside is considerably more drab; the dark colors give the insect its common name, because early entomologists thought it looked like the drab cloaks worn by mourners at funerals.
Mourning cloaks often overwinter in sheltered, and begin flying on the first warm days of spring.

image: http://commons.wikimedia.org/wiki/File:Mourning_Cloak,_Mer_Bleue.jpg

Mourning Cloak Butterfly

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American Dagger Moth Caterpillar Identification

This cool caterpillar has irritating "fur" that it spins into its cocoon. The black hair pencils may act as fake antennae, making the insect appear larger or more threatening than it really is. This caterpillar feed on oaks and other trees, and can be very common in the late summer and early fall as it crawls around looking for a place to spin its oval cocoon.

American Dagger Moth

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Tiger Swallowtail Caterpillar Identification

This rather plain caterpillar turns into one of our most spectacular butterflies, the tiger swallowtail (Pterourus glaucus). It is sometimes seen crawling down the trunks of ash and cherry trees in early summer, looking for a place to pupate. This caterpillar overwinters as a very young larvae, rolled up in a little leaf shelter, to emerge in the spring and resume eating and growing. The adult butterflies are a common sight in parks and gardens, yellow and black beauties that soar high among the tree tops, looking for mates and a place to lay their eggs.

Tiger Swallowtail

White-Marked Tussock Moth Caterpillar Identification

Look Familiar?

These cool-looking caterpillars produce a quite plain and inconspicuous moth. They eat almost anything, including a number of decorative trees like hawthorn that cities tend to plant along roads and in plazas. Tussock moth caterpillars get their name from the little tufts of fur along their backs; apparently these are called "tussocks" in some parts of the world.

Puss Moth Caterpillar Identification

With its awesome pompadour and general slug-like build, this animal is sometimes referred to as the "Elvis Caterpillar." Puss moth caterpillars belong to the Megalopygidae family, which has a fair number of interesting-looking caterpillars. Many of these caterpillars have stinging hairs -- including the puss moth, which sometimes drops out of trees onto unlucky passersby! The sting of the puss moth is usually mild, though sensitive individuals can develop a more intense reaction.
Megalopygidae moths are relatively uncommon, and if you see one you're lucky -- but don't touch!

Spicebush Swallowtail Caterpillar Identification

This is a cool caterpillar with fake snake eyes. The effect is even better when it sticks out its "osmeterium," a red, forked organ that it can stick out from behind its head when it's feeling bothered. The osmeterium looks a lot like the forked tongue of a snake, and it also smells bad. Pretty good defense for an otherwise tasty caterpillar! This one turns into the big, beautiful spicebush swallowtail.

Spicebush Swallowtail