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How to Raise a Caterpillar to a Butterfly or Moth

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The caterpillar of the black swallowtail butterfly. It eats the leaves of dill, and parsley, and carrot plants.

The caterpillar of the black swallowtail butterfly. It eats the leaves of dill, and parsley, and carrot plants.

Caterpillar Basics: What Does Your Caterpillar Need?

This is the first question you need to ask, and you need an answer fast. Caterpillars are wild animals, and they don't always do well in captivity. If you quickly provide the caterpillar with what it needs, it has a good chance of living to its adult form.

Here is a list of three basic needs. I will discuss each one in more detail below.

3 Essential Caterpillar Needs

  1. Food: If you found it on a plant, then it almost certainly eats the leaves from that plant. If it was on the ground, then it's a little more complicated.
  2. Habitat: Caterpillars need to have an appropriate place to live.
  3. Patience: Let your caterpillar live its life and develop on its own schedule. This can take weeks. The pupa stage often takes several months, depending on some key factors.

Caterpillar Basics: What Do You Need to Know About Your Caterpillar?

A caterpillar is the immature form of a butterfly or moth (order Lepidoptera). It is also called a "larva." The caterpillar you found began as a tiny hatchling from an egg laid by an adult female. It will shed its skin several times as it grows, and when it's done growing it will shed its skin one last time and become what is known as a "pupa." Some moth caterpillars spin a cocoon around themselves before the final change into a pupa, but the pupa of a butterfly typically hangs from the food plant and is called a "chrysalis."

Inside the shell of the pupa, an amazing change takes place: the insect develops wings, long legs, and all of the other parts of the adult. When the time comes, the adult wriggles out of the pupa shell and flies away, to mate and lay eggs. This cycle is known as "complete metamorphosis," and many other kinds of insects go through the same process, including beetles, bees, flies, cicadas, and dragonflies.

Great Video of Complete Metamorphosis:

#1 Food

Virtually all caterpillars eat leaves, but most of them are very picky. In fact, your caterpillar will probably only eat one kind of leaf, and possibly from only one specific tree or plant in your yard. It will almost certainly not eat lettuce from your refrigerator or leaves from one of your house plants..

If you found it on a plant, great -- that's what it eats, and you can start giving it fresh leaves from that plant. Make sure you clear out old leaves and poops, and provide clean fresh leaves every couple of days. Be careful not to import any ants or other predators on the leaves! I always rinse food plants before I give them to a caterpillar.

If you found it somewhere other than on a plant -- like crawling on the ground, or on a building -- then it is probably looking for a good place to become a pupa. This means it is done eating. You should give it a "salad" of leaves collected from trees and plants in the vicinity, and it may eat, but if it doesn't that means it's ready to shed its final skin and begin the transformation into an adult moth or butterfly.

This is the caterpillar of the spicebush swallowtail butterfly.

This is the caterpillar of the spicebush swallowtail butterfly.

#2 Habitat

First, be VERY careful with the caterpillar. They're quite fragile, and can be easily bruised or damaged.

Basically you want to create the ideal habitat for your caterpillar to turn into an adult. It's not difficult, but there are a few things that matter very much.

  • Step 1: Get a clean tupperware container, ideally at least 5 inches square and 3-4 inches high. You may want to order a special "Bug Habitat"
  • Step 2: Fold a paper towel and put it in the bottom of the container.
  • Step 3: Place a plain dry stick or popsicle stick (or two) in the container
  • Step 4: CAREFULLY place the caterpillar in the container. If it's on a leaf, place the whole leaf in along with the caterpillar.
  • Step 5: If the caterpillar was on a plant and is still eating, keep fresh leaves in the container until it pupates.
  • Step 6: If the caterpillar poops, clean it out. You may need to change the paper towel occasionally.
  • Step 7: If the caterpillar crawls into the paper towel and disappears, don't worry! It's probably hiding before it pupates.
  • Step 8: After it pupates, keep an eye on things. Eventually it will hatch into an adult!

#3 Patience

The development of a caterpillar from larva to adult takes a lot of time, and for much of that time, it will look like nothing is happening. It can even be hard to tell if your caterpillar is alive or dead. The pupa stage can last for weeks, and often months -- many species pupate for the entire winter and hatch out the following summer.

It's very important that you don't forget about your caterpillar. Keep it somewhere that you can check it every few days to see how things are going. You may be surprised by the sudden appearance of a beautiful adult moth or butterfly!

On the other hand, don't bother the caterpillar or pupa too much. Try to avoid handling it unless you have to. Remember that this is a wild animal, and it's not used to being in captivity!

The cool larva of the wild cherry moth

The cool larva of the wild cherry moth

Caterpillar Identification

There are good resources online for identifying your caterpillar. I have an article on Owlcation that may help you, and you can also do a quick Google search. But I can tell you this in advance: Your caterpillar is probably a moth.

Why? There are a couple of reasons, but here's the main one -- while there are maybe 400 species of butterfly common enough for you to ever encounter one, there are over 10,000 species of moths! Many of them are small and not very noticeable, but there's still a huge overbalance of moths compared to butterflies. Plus, moths tend to be more common from species to species, and will sometimes "explode" into huge outbreaks of millions of individuals, or even just a few hundred crawling around outside your house. Butterflies almost never do that -- when you find a butterfly caterpillar, it's usually alone and on a plant, where caterpillars are generally hard to find anyway. Taken all together, for every one butterfly caterpillar you find, you'll come across maybe 20 different moth caterpillars.

But moths are cool! They are some of the most gorgeous and under-appreciated animals on the planet. So raise that caterpillar to adulthood and see what you've been missing.

A gorgeous giant silk moth

A gorgeous giant silk moth

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How to Raise a Caterpillar: Was It on a Plant?

It's important to think about exactly where you found your caterpillar. This is because caterpillars almost always stay on the plant that they eat to survive. Since caterpillars eat leaves, they need leaves to eat when you raise them. But you can't just go outside and get a handful of leaves and grass and expect them to eat it. That would be like someone making a big plate of raw eggs and dog food and grass and expecting you to eat it. Like you, caterpillars eat only certain foods – often the leaves of only one or two kinds of tree or bush.

Think about where you found your caterpillar, and make sure you supply it with fresh leaves from the same plant you found it on. Keep it in a tight tupperware container, or a jar, with a vertical stick or two in case your caterpillar is in the mood to climb. Don't forget to change the leaves every couple of days. There will be poops – caterpillars poop A LOT – and you need to clean these out or mold might grow, which is not only gross but also dangerous to your caterpillar's health.

Caterpillars do need a good amount of attention, but after a while, your caterpillar will make a pupa or a cocoon. Keep reading for more information about that!

This cutworm caterpillar will turn into a pretty brown moth.

This cutworm caterpillar will turn into a pretty brown moth.

How To Raise a Caterpillar: Was It on the Ground?

Maybe your caterpillar wasn't on a plant, but was crawling around on the ground, or on a tree trunk, or on your porch. If that's the case, then your caterpillar is trying to tell you something, and it's this: “I'm about to pupate!”

Usually the only reason a caterpillar will leave its food plant is to find a place to make a cocoon or a chrysalis. As a matter of fact, that's when you're most likely to find a caterpillar at all. When they decide it's time to pupate, caterpillars often leave the plant they've been eating and crawl a little ways away, looking for the perfect place to turn into an adult.

An immature larva of a giant silk moth.

An immature larva of a giant silk moth.

Some Caterpillars Pupate in the Ground

Many moth caterpillars can be divided into diggers and spinners. This is because when it's time to rest (pupate) and turn into an adult, they do one of two things: dig down into the ground, or go somewhere quiet and spin a cocoon.

Many moth caterpillars crawl a little ways away from the food plant and then dig down a few inches into the ground. There they shrug off their skin, and underneath is a brown, nut-like pupa that will soon hatch out into the adult moth. If you found a caterpillar crawling on the ground, put it into a "Bug Habitat". Don't worry about airholes – the caterpillar will be fine with the amount of air in the container. Chances are a caterpillar that you found on the ground will dig around in the paper towel for a day or two, and then turn into a smooth brown pupa. If it does, congratulations! You have made that caterpillar very happy by giving it a nice comfy home in which to turn into an adult.

Watch as a Silkworm Spins Its Cocoon

The true silk moth, species Bombyx mori, doesn't occur in nature anymore -- they're found solely in places that use them to manufacture silk. That's right -- all silk fabric is the product of an insect! The silk begins as a liquid, and when it hits the air it hardens into a strong thread of silk.

What's Inside a Cocoon?

Many moth caterpillars spin a cocoon to shelter the pupa inside. But many don't, preferring to dig into the ground and make a pupa there. Either way, the moth pupa will look a little like a peanut with beautiful designs etched onto it. These are the outlines of the adult moth's legs, mouth-parts, and antennae.

Some people find their caterpillar looking like this and assume it has shriveled up and died. Nothing could be further from the truth! Your caterpillar has just gone into a phase of complete metamorphosis. Given time, the adult will hatch out and fly away to mate, lay eggs, and complete the cycle.

A Moth Pupa


Some Caterpillars Pupate on Plants

Sometimes the caterpillar you find will spin a cocoon.But you can use the same bug-habitat method described above. The difference will be that the caterpillar makes a little shelter for itself before shrugging off its skin and becoming a pupa. All cocoons have a little pupa inside them. If your caterpillar spins a cocoon, cool! Inside it's changing into an adult moth.

This is the chrysalis of the black swallowtail

This is the chrysalis of the black swallowtail

I Think My Caterpillar Died!

Wait! Don't give up yet. It's easy to think that your caterpillar has died, when actually it's only turned into a still, brown pupa. Inside it's very much alive, and all of its cells are rearranging themselves into a completely different-looking kind of insect – a full-grown butterfly or moth. Don't give up, and don't throw it away. If it actually is dead, it will dry up and turn into a little shriveled raisin-like thing. Then it's dead, and it's time to say goodbye. But usually it's just resting and changing!

This photo shows a typical pupa -- if your caterpillar looks anything like this, then never fear -- it's fine.


Parasitic Wasps and Flies Often Kill Caterpillars

If your caterpillar stops moving and little white things suddenly appear on it, that's bad.

It's very common for caterpillars to be attacked by a tiny wasp or fly called a "parasite." These insects lay eggs on caterpillars, and then the tiny wasp or fly larvae live inside the caterpillar, eating the internal fat stored by the caterpillar. Amazingly, this doesn't kill the caterpillar. At least not right away.

Over time, these little wasp or fly larvae get bigger and bigger, until it's time for them to spin their own little cocoons (that's right, some wasp larvae spin cocoons of their own before they hatch into grown-up wasps -- which just shows how wasps and butterflies are related).

When it's time to spin their cocoons, the little larvae do what they have to do -- they tunnel out of the caterpillar's skin and spin cocoons on the surface. That's why you see all those little white things -- those are the cocoons of the parasitoid wasp larvae. Soon they'll hatch into little black wasps and fly off to repeat the process.

This is all very bad news for your caterpillar. The condition is 100% fatal. But it's a really cool lesson in how nature works. Nature is not sentimental. Either the wasps die from lack of food or the caterpillar dies -- either way, someone dies. And anyway if these little wasps didn't exist, you and your house would be submerged under an ocean of caterpillars.

Hey, My Caterpillar Turned Into a Butterfly! (But it is Probably a Moth)


The day will come when you look in on your caterpillar and see a new insect in the cage – an adult moth or butterfly! It's a really excellent moment, and congratulations are in order. If you can, look in a book or online and try to find out what it is. If you want to start a collection, pop the insect in the freezer for a few hours – that will kill it, and you can spread out the wings, make a label, and begin a scientific collection. Otherwise just let it go. It will fly away, mate, and lay eggs that will turn into the next generation. Way to go!

Take a Caterpillar Poll!

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