Raising Giant Silkmoths – Cecropias, Polyphemus, Prometheas

I’ve been raising Cecropia, Polyphemus and Promethea moths for a few years but I’m still learning about the best ways to do it. Here are instructions based on my experience so far.

The instructions are for eastern Minnesota and west-central Wisconsin – the timing in other places may be different. If you have ideas or other methods that work well, please write and let me know – I’d like to try them.

I raise mostly Cecropia and Polyphemus moths, but I’ve been trying other species too.  This year I’ve been raising Prometheas, and I have some Buck Moth pupas that I’m hoping will hatch so I can try raising them.  In 2011, I’ve been raising Luna moths.  One advantage of these Giant Silk Moths (the family Saturniidae) is that the adults don’t eat, so it’s possible to keep them for a day or two to try to mate them and get eggs.


Cecropia and Polyphemus Moths hatch from their cocoons in late May or June. They mate and lay eggs in the next day or two – adult moths don’t eat, so they only live for a few days. The caterpillars hatch a week or two from when they were laid. The caterpillars eat and grow all summer, and make their cocoons in August or September. They over winter as cocoons, and the adults emerge the following June to start the cycle over again.

Raising the Moths – Cecropias

Eggs to Caterpillars

Eggs are laid on whatever happens to be around when the female has finished mating. If she’s in a cage, she’ll usually lay them on the walls of the cage. If you put a paper bag in the cage, she’ll lay at least some on the bag, which makes the eggs easier to move or give away.

These eggs were laid on a brown paper bag. They’re about 1/8 inch long.

Keep watch on the eggs, and a week or two after they were laid, the caterpillars will start to hatch.

Hatched eggs


At first the caterpillars are tiny – less than half an inch long – and black with black spines.
First instar caterpillar

Caterpillars’ skin doesn’t grow, so when they get too big for their skin they shed it and expose a new larger skin underneath. Each of these stages between shedding is called an “instar”. Caterpillars will go through five instars before making their cocoon. The skin of each instar is a little different. Here are some later Cecropia instars.

Second instar

Third instar

Fifth instar

Caterpillar Food

The caterpillars will need to start eating right away.

Cecropia caterpillars will eat many different kinds of leaves, but once they start eating, they like to keep eating the same thing. So choose a kind of leaf that you can get plenty of. Be sure you don’t have to collect it near a golf course or anywhere there may have been chemicals sprayed to kill insects.

Here’s a list of possible food plants: wild cherry, apple, elderberry, box elder, maple, birch, willow, linden, elm, and lilac. I’ve tried using elderberry and lilac, and the caterpillars are happy to eat either. I usually use lilac because I give most of my caterpillars away, and most people have access to lilac.

Where to keep your caterpillar

The caterpillars need to be in a cage.

If you are starting with eggs, or small caterpillars, the cage needs to be very secure – with no holes or cracks.  When the caterpillars first hatch they go looking for something to eat.  If they find a crack in the cage before they find the food, they may escape.

If they are going to be outside the cage should keep them safe from predators – birds, mice, cats, insects and spiders.  If the cage is going to be outside, the screening material should be very fine mesh – smaller than window screening.  The holes in window screening are large enough to admit some insects that prey on caterpillars.  I keep my cages on a screened porch.  The two layers of screening – one on the porch and one on the cage – seems to completely exclude predators.

If the cage is made of glass, be sure to keep it out of the sun. The sun heats up the air inside and will cook the caterpillars.

Examples of cages you can use are:
Large glass jars with screen/mesh tops
Aquariums with screen/mesh tops
Old bird cages with plastic screening or fabric wrapped around the outside
Hand made cages using wire, plastic or wood, and wrapped with plastic screening material.
Plastic boxes covered with screening or fabric

Here are two kinds of cages I make for my caterpillars.

This cage is especially good for small caterpillars.  It’s a plastic box, with a lid that snaps on.

I cut out the center of the lid, lay a piece of gauzy fabric over the box, and snap the lid edge on over the fabric.

Here’s the box with caterpillars inside, and the fabric draped over the top.

Here it is with the lid snapped on.


This cage is better for older caterpillars.  It has small cracks between the top and bottom and the sides, so if the caterpillars are too small, they can escape.  Sometimes, if they start to run out of fresh leaves, I find caterpillars crawling around on the outside of the cage.  But large cages like this – made with 20 inch saucers and 2 feet high – will hold 10 or 12 large caterpillars.

Plastic coated fencing that comes in 2 foot high rolls
Plastic screening (also comes in a roll)
2 large (20 inches in diameter) plastic saucers (the kind that are used under large plastic plant pots)
Needle and thread

Unroll enough of the fencing to make a cylinder that exactly fits inside one of the plastic saucers. Cut and fasten the wire cylinder together.
Cut and sew a piece of plastic screening around the outside of the fencing.
Use the two saucers as the top and the bottom of the cage.

Smaller cages, like glass jars, should only be used if you’re raising one or two caterpillars. It’s better to use larger cages for larger numbers of caterpillars. If the caterpillars are too crowded they may get sick.

Feeding your caterpillars

You need to find a way to offer the caterpillars fresh leaves but protect them from drowning. Caterpillars aren’t very smart about open water, and if the stems of the plants are in a jar of water, they will climb down the stems and drown.   Access to the water can be blocked with a crumpled piece of waxed paper or plastic wrap stuck between the stems.  Or you can put the water in a plastic container with a plastic lid.   Punch a few holes in the lid for the stems to go through.  (Be sure all the holes are filled – or cover unused holes with tape – the caterpillars will find any open holes.)

Here’s an example of a plastic water container.


Put fresh leaves in when the old leaves look wilted. Usually the caterpillars will move to the fresh leaves quickly, but check the wilted leaves before you throw them out to make sure you aren’t throwing out any caterpillars.  (To be sure I don’t throw out any caterpillars, I put all the used leaves into a bucket – a clean 5 gallon plastic pail works well – along with some fresh leaves. If I check on them the next day, any caterpillars that I missed will have found their way onto the fresh food.)

When I move the caterpillars to the fresh food, I try not to touch them.  They seem to do better without much human contact.  There are a few other reasons not to touch caterpillars: they can get sick from bacteria from your hands; they are fairly fragile, and even light squeezing isn’t good for them.  Also, some have stinging spines (Cecropias and Polyphemus don’t, but Buck Moth and Io Moth caterpillars do, and the spines can cause painful irritations on your skin).

Cleaning cages

The caterpillars produce “frass” – droppings – which will need to be cleaned out. When the caterpillars are small, the frass will be small, but when they get larger, the frass will be larger and messier. Clean the cages often, washing them with soap and water, so the caterpillars don’t get sick.

At the end of August or the beginning of September the caterpillars will be about as big as your thumb and ready to make their cocoons. They’ll wander around for a while, looking for a suitable place, and then begin building. They might build on the bars of the cage or on the lilac sticks.

They start by throwing out silk, like spider silk, all around themselves.

They slowly surround themselves with more and more silk until they’re in a white silken cage.

Then over the next day or two, the cocoon will turn brown and you won’t be able to see the caterpillar any more.


After the cocoons are finished and the weather is colder, you need to put them outside so they can go through the cold of the winter. It’s best to leave them in their cage, and put it in a garage or porch that’s the same temperature as outside. Protect them as well as you can from mice and other animals that might nibble on them.

This outdoor stage is very important – they need to go through a winter because it keeps them on the same schedule as the moths in the wild. When they hatch, there need to be other moths hatching so they have partners to mate with.

They are well adapted to survive our cold Wisconsin and Minnesota winters. If you keep them in a place where they are protected from snow, it’s a good idea to sprinkle them with snow periodically, or spray them with water so they get enough moisture.


The next spring the moths will emerge sometime between the middle of May and the middle of June. The warmer the weather, the earlier the moths will emerge. When it gets close to the right time, check the cocoons every day to be sure not to miss them. It’s a good idea to keep the cocoons outside at least until they start hatching.


The moths will usually emerge in the middle of the day, and spend the day pumping up and drying their wings.
Here is a series of photos of a moth emerging. This happens very fast – it takes less than a minute – so this is the only time I’ve been able to watch it.

This is a newly emerged moth before its wings have expanded, with the empty cocoon below.

Here’s a link to a short video Mike took of a moth pumping up his wings.

By the time it gets dark they’re ready to fly.

Now you have to know if you have a male or a female moth. Males have very large, feathery antennae. Female antennae are much thinner. Here are some photos to help you see the difference.



If you have a male, release it when it gets dark. If you let it go in the light, it will be visible to predators and it may get eaten.

If you have a female, you have a choice – you can let it go, or you can keep it for another day and watch for a male to come to mate.


The job of the adult moths is to mate and lay eggs. They don’t eat at all, so they have to get everything done in a few days.

The female moths don’t fly very far – they sit in one place and send out pheromones into the air to attract males. The males scent these pheromones and fly to the females. The males usually arrive very early in the morning just before it gets light. The males fly around, getting closer and closer to the female, until one flies in close and begins to mate.

The mating pair will stay coupled until the next evening. Just before dark they’ll separate and the female will fly off to lay her eggs, and the male will fly away to try to find another female.

If you want to mate your female, keep her in a cage all that night, next to an open window, on a screened porch, or outside, so she can send out her pheromones. Then get up very early the next morning to watch for males. In my experience they always arrived between 4 and 5am. I would bring the cage outside, and wait until I saw the males coming. Then I would open the cage and watch. The female will just sit in the cage, waiting. The males will fly around the cage, flapping their wings against the cage and the walls of the house, and against you. Then, eventually, one of the males will dive in and start to mate. Almost immediately the other males will fly away.

If you don’t want to stay up all night, you can put the female in a cage with large enough holes to allow her to mate through the cage.  Here’s one of the mating cages I use.  It’s made with 1/2 inch plastic coated hardware cloth, bent into a cylinder, with plastic plant saucers for the top and bottom.  You can put a female in one of these cages, put it outside, and in the morning, you’ll usually have a male clinging to the outside, and mating with the female.

mating cage


Close the cage and bring it inside for the day. The mating pair will stay coupled until the next afternoon or evening.

Release the male as soon as it gets dark. You can either release the female then, or keep her for a while, until she lays some eggs in the cage, and then release her to lay the rest in the wild.

Don’t forget – if she lays eggs in the cage, they will hatch in about a week, and you’ll either have to feed them, or release them onto a plant that they can eat.

Other Species:

Polyphemus – life cycle is very similar to Cecropias.  Differences: the adults tend to emerge a week or two earlier.  Mating takes place in the middle of the night – usually at 12 or 1 in the morning.  The caterpillars make their cocoons on the ground – or the floor of their cage – wrapped in a leaf.  Although I’ve seen long lists of foods that the caterpillars will eat (maple, birch, ash, etc.) I’ve found that my caterpillars are healthiest when they eat oak leaves.

Polyphemus female

Promethea – life cycle similar to Cecropias.  Differences: adults are somewhat smaller, and the males and females have different coloring.  Mating takes place in the late afternoon – usually between 3:30 and 7pm.  I’ve been feeding my caterpillars Wild Black Cherry leaves, but the list of foods they should be able to eat include apple, ash, basswood, birch, lilac, and maple.

Promethea female

Promethea male

Here are a few other links you might be interested in:

Luna Moths – my experiences seeing and raising them

Buck Moths

How to raise Monarchs

How to Raise Other Butterfly Caterpillars

BugLifeCycles – a site I built to document the life cycles of all kinds of insects