Raising Saturniid Moths

This article was reprinted with permission from Liz Day's personal home page. Our thanks to Liz for this fine article.

CARE OF SATURNIID MOTHS

Beginner-level info for rearing Polyphemus, Luna, Cynthia, Cecropia, Promethea, Io, Regal, and Imperial moths. (The first 3 species are the easiest to rear.)

by Liz Day (see acknowledgments at end)
N.B. This info is free, but it's also COPYRIGHTED 1998. You can make as many copies, hard or cyber, as you want, and give them to whomever you want, as long as you don't do so for profit, and as long as my name as author and this notice stay intact here at the top. If I find this piece floating around without attribution, I will hunt you down, and you will wish I hadn't. Thanks.

Eggs

Keep the eggs in a small container with the lid closed, so the larvae don't escape when they hatch. If the air is very dry, mist the eggs occasionally. Never put leaves in with the eggs - the leaves give off CO2 and the eggs may suffocate. For the same reason, the container should not be totally airtight.

Things to see:

Often the newly-hatched larva eats its egg shell for protein.

Young larvae

The main problems with just-hatched larvae are that they sometimes crawl off their food before they begin to eat, and they can dry up and die quickly. To prevent these problems, I keep them in a Tupperware-type plastic container with the lid closed. Put a sheet of damp paper towel on the bottom and lay the leaves on it. Use leaves that are mature, but not old and leathery; do not use young new leaves. This arrangement makes it easy to keep track of the caterpillars, and keeps them close to their food. The humid air keeps the leaves alive and the larvae from drying out when they are very small. Once a day (twice is better): empty the container and rinse it, replace the paper towel with a new one, rinse or knock off any droppings stuck to the leaves or the larvae, and replace errant larvae on the leaves. (Never pull larvae off the paper towel, though - instead cut out the little piece they're on.) Adjust the amount of water you leave in the towel, so that when you close the lid, the environment inside the container will be humid but not wet. Make sure the larvae themselves are not wet. Excessive dampness promotes disease.

I keep larvae in this container until they have molted at least once. You can tell if they've molted because in most species they change color and appearance with each molt, and because the head capsule is much larger at each new stage ("instar").

You may want them to switch to another food plant species partway through their development. Sometimes this can be done, and other times they will refuse to switch. Put them on the new kind of food, replace them if they walk away, and watch closely to be sure they're eating it. An ideal time to switch foods is right after a larva has molted, before it gets started on the old food again. At this time it hasn't eaten in a few days and is ravenous.

Things to see:

In some species, young larvae cluster together on the leaf. This may keep anyone from being isolated on a leaf edge where it could fall off when another larva chews through the leaf closer to the base; or perhaps clustering has some anti-predator effect.

Larger larvae

Wild saturniid caterpillars live up in trees, where they are surrounded with free-moving, warm, humid, summer air. Avoid air conditioning, which is cold and dry; it will slow their growth and dehydrate them. Don't keep larvae closed up inside a container where the air will get excessively damp and stagnant. (When small larvae live in plastic containers, I open and clean the containers every day. I don't keep larger larvae closed up like this.)

In the wild, their droppings fall to the ground far away. Thus, don't let them sit in old leaves and frass (droppings). Larvae are susceptible to many fungal diseases, and to a virus that kills them just before they pupate. The virus has no cure, but many diseases are transmitted by one larva eating or being in contact with the droppings of another, by the rearer handling sick larvae, by dripping water/excess dampness, and by fungal spores that grow in damp droppings. If you see a sick caterpillar, get it away from the others; if you see one with droppings sticking to it, rinse it clean under the faucet. Knock or rinse any droppings off the leaves.

(Please note that sooner or later, you will surely lose some or all of a brood to disease. Every rearer experiences this, no matter how well they care for their larvae. Luna and polyphemus seem to be the least prone to illness, but no species is immune. Don't beat yourself up if some die.)

In the wild, saturniid larvae get some amount of sunlight. They apparently need natural light or its equivalent to survive, but no one knows exactly what kind of light or how much. Mine have done well in summer shade. Be careful with direct sun - it's hot!

I keep my larvae either outdoors, or indoors by an open window. They live on branches stuck in a vase of water. If they are outdoors, all this is enclosed in nylon bridal mesh (buy at fabric stores). The mesh keeps predators out and the caterpillars from walking away. You can also put them out on tree branches inside mesh sleeves. I remove frass every day. Plug the mouth of the water jar with a wad of paper towel so the larvae can't crawl down into the water and drown.

The keys to success are cleanliness and fresh, abundant food. Don't let them run out of food. They eat (intermittently) 24 hours a day, especially at night.

Larvae can drink water, but they obtain most of the water they need from their food. They will reject leaves that are drying up. I cut the stems twice a day, because otherwise the cut end seals up and the leaves dry out.

Avoid crowding them - they interfere with each other, which will stunt their growth. Crowding also lets diseases spread. Saturniid caterpillars are not cannibalistic, but might inadvertently bite each other. One caterpillar per leaf is about right.

When handling, don't pull a caterpillar off a surface - the body will break open before the legs let go. Injured caterpillars die. Instead, cut off the whole leaf the larva is sitting on, and move that to where you want it. When giving them fresh leaves, I just lay the old leaves, stems, larvae and all, onto the fresh ones and let the caterpillars crawl to the new food.

When a caterpillar molts, it steps out of its skin. However, first it must attach the outer skin to something so it won't fall off the plant. Before shedding, the larva spins a silk pad, and hooks its feet to it. Sometimes you can see the pad, or you may just see the caterpillar sitting there motionless with its head curled under. They sit this way for about 2 days before shedding. You can tell if one is stuck by squeezing its rear end; if stuck, it won't start to walk. You can also see the head capsule becoming detached from the face; this is the first stage of molting.

Don't disturb them when they're like this. Just cut the whole leaf if you need to move it. Sometimes you will see a caterpillar that has not completely shed its skin - part of the old skin remains wrapped around its middle like a belt. This is probably caused by it having been moved while in the process of shedding. If this happens, try to carefully tear or break off the belt of old skin.

After shedding, they will be very soft. Avoid handling their bodies then, just hold their leaf. They are vulnerable to attack by ants at this time, especially if they get wet or fall on the ground. I lost many larvae during a rain when they were molting.

Yellowjackets will attack the caterpillars and kill them if they aren't screened out. Tiny Braconid wasps (like those that make cocoons on the bodies of tomato worms) and large Ichneumon wasps are parasites of Saturniids, but the mesh will usually keep them out. Predatory bugs occasionally stab them through the mesh if the caterpillar is sitting right on the inside of the mesh where it can be reached. Birds haven't been a problem so far for me; I think they don't see the pillars under the mesh. Ants seem to bother larvae under some conditions and not others. Some friends report that if ants gain access to their larvae, the larvae are all devoured; whereas I have watched predatory ants walk right over larvae every day day for weeks and ignore them. Watch your situation carefully to see what is happening and whether you need to keep ants out.

When larvae are ready to pupate, they will get what looks like diarrhea - they are emptying their gut to be ready for the next stage. They evacuate their gut in one or two big messes. They also start to wander; in the wild, some species would crawl down off their tree and walk away. At this point you must enclose them so you don't lose them. (Cautionary stories of escaped pillars turning up in funny places omitted).

Things to see:

A caterpillar's eyes are small and primitive - just little dots on the head capsule near the mouth. They don't see very well.

Molting larvae shed their head capsule first. You can see it separating from their face before it falls off. They cannot eat at this time because it's covering their jaws. After the capsule goes, the rest of the skin is shed quickly. Often they eat their shed skins.

Large heavy larvae often will prefer not to crawl onto the leaf stalk (petiole), a precarious hold. Instead they will hold onto the main stem with their hind legs, and use their front legs to bend and pull the leaf towards their mouth. They may snip the leaf vein to make it easier to bend.

Don't touch io moth larvae - they sting.

With other species, if you pet your larvae often as they get bigger, they will get used to being touched and not mind. Some people say that handling will make the larvae use up too much energy reacting to the touches. This has not been my experience.

Prepupae

Inside the cocoon, or underground, before it sheds its skin and turns into a pupa, the larva becomes something called a pre- pupa. It shortens a little and can't walk anymore.

Pupae

Most saturniid caterpillars spin a cocoon in leaves on the tree or on the ground. Sometimes they spin right in the leaves they've been eating; other times they walk off their foodplant and march away. If they do that, put them in a paper bag and fold over the top. Regal and imperial larvae do not make cocoons - they burrow into the ground, and need different treatment (below).

Some species have more than one brood a year. The spring and summer broods develop into moths right away: their pupae hatch out in a few weeks. Autumn broods will not hatch until they have first gone through a cold period (winter). The "decision" of which way to go is made while the animal is still a larva; you can't change it by the way you treat the pupa. The matter is not totally understood. Research suggests that the crucial thing is the daylength during the larva's final (5th) instar: a light period longer than 12 hours (like that in early summer) will cause the pupae to try to develop and hatch right away, but shorter daylengths produce pupae that need to hibernate ("diapause"). I avoid keeping later broods under electric lights after dark, in hopes they will not try to emerge as moths so late in the year that there are no leaves left on the trees for their offspring. But I'm not sure it really matters - they might be taking their cue from the natural light through the window instead.

If you try to put a pupa that is "programmed" for immediate hatching into the cold, it will just die. When pupae are in warm temperatures, any pupae that don't emerge within 6 weeks are either dead, or in diapause.

Pupae still breathe; they have spiracles (breathing holes) down their sides. They can't dry out too much or will die. They can't be kept too wet or will mold/rot.

Store cocoons outdoors, out of the sun, in a rodent-proof cage. Birds, mice and chipmunks eat pupae! One can make a cage out of hardware cloth, which is also useful for containing the moth when it hatches.

Give imperials & regals about 6" of moist peat moss to burrow into, where they will pupate. Peat moss, which is fairly germ- free, seems better to me than soil, which is not very clean. Avoid vermiculite and other materials that are too loose/coarse to hold their shape. If the little cave that the larvae has dug collapses on it, the animal can get deformed when it molts into a pupa.

Even if there is nowhere to dig into, the larva will eventually pupate anyway. Thus, you can also just put the larvae in a container with damp paper towels and let them pupate in "the open". Make sure there is humidity. This is a good way to observe the molting, which is strange to see.

After they dig in, you should wait at least two weeks before disturbing them, since they may still be soft under the ground. The caterpillar molts into an egg-shaped pupa that first is greenish, then turns dark brown and hardens.

Their winter care is something of a pain. My friend had nearly all of his rot over winter for several years until he discovered how to keep them.

He stores imperial and regal pupae in the frij, in a special Tupperware arrangement. (If pupae sit in the open in a frost- free frij they will dehydrate and die.) Get a piece of 100% linen (avail at bridal stores). Linen will not get wet in damp air. Lay the linen over the top of the plastic container like a hammock (the closed lid will keep it from falling down). Put a small amount of water in the bottom of the container, suspend the pupae in their hammock over the water, and close the lid. The linen does not get wet, but the air is kept humid. I open the container every two weeks, check the water level, and blot up any condensation on the lid or pupae. This system should also work for other species.

My friend does not put air holes in the container. However, I fear that they could eventually suffocate if sealed up for too long. So I open the container every so often. Or you could put in some air holes.

Regal and imperial pupae can take freezing temperatures in the frij, but not for very long. Keep the temp above freezing.

When it gets cold outdoors, that is the time to start the pupae's cold period. They need to be acclimated to cold. Keep them somewhere where they will gradually get cold over a period of at least a week, as it does outdoors, before putting them in the frij. In spring, take them out of the frij whenever it warms up outside, and put the pupae back into peat moss, in a flowerpot, inside a cage, outdoors. I water it often enough to keep them from drying out. The adult is able to crawl out of the peat when it hatches.

To see if a pupa is alive or dead, carefully poke it in the leathery area between two abdominal segments with something dull like your fingernail or the edge of a piece of paper. They hate this; live ones will squirm. Other clues: live ones weigh more (they sink in water) and are glossier than dead ones.

All the native large saturniids overwinter as pupae, never as eggs.

Things to see:

Watching the larva actually shed its skin and become a pupa is a strange experience. The new pupa is not smoothly fused together over its surface - the head, antennae, and wings are still detached at first and the very soft pupa slowly pulses and scrunches its head into a concave position like a rubber toy being punched in. To see this, however, you must cut open the cocoon (maybe they could be induced to spin one against something transparent?), dig up the prepupa from the soil, or have allowed one to pupate in an empty container as described earlier for regal/imperial moths. There is danger of injuring the animal; also, before you disturb it, be sure the pupating larva has become a prepupa and is no longer able to walk. Otherwise, finding its cocoon gone, it will spin another one, using up a lot of its energy reserves. One spiracle is in front of the wings.

To sex pupae, look at the underside near the tail. 4 abdominal segments below the wingcase, there is an area where the edges separating the segments seem to disappear or run together down the center. In females, this area is smooth and blank. In males, there are two little bumps right next to each other, where the genitalia will be.

One can indeed get silk from the cocoons of these "giant silk moths". However, the silk is an inferior grade to that made by the (unrelated) domestic silk moth raised in China.

Adult moths

Emergence from the pupa is triggered by many factors, including temperature and day length. When the moth hatches, its wings come out all crumpled up; then the moth clings to something while the wings expand and dry. Thus, the moth will need something it can crawl up and hang from vertically. It must be able to hang freely, or the wings will dry crumpled up. Keep screen or sticks near the pupae for the moths to climb.

Warning: newly emerged moths squirt out a liquid that stains (it's the waste they made while inside the pupa). Keep the moth away from curtains/rugs etc. that you don't want stained.

Adult saturniid moths do not eat. They live off their fat. They only live a few days. Females are bigger (both fatter in the body and larger in the wingspan) than males, and have narrower antennae - the male's are wider and feathery.

After the male moth emerges, he flies away and starts searching for a female. When the female moth emerges, she crawls up a branch and just sits there. She is disinclined to fly until she has finished "calling". At whatever hour of the day or night is right for that species, the female "calls" for males by emitting pheromones. She sits still and lets her abdomen hang down so the pheromones come out. You can see a little brown/yellow thing sticking out the tip of her abdomen. Males can smell the pheromones from at least a mile away, and fly upwind to find her. They will try to reach her and mate with her only as long as she puts off the smell. If she doesn't get a male the first night, she waits and tries again the next night. However, after a few nights, she will give up, stop calling, and flap around dumping infertile eggs.

Mating in some saturniid species takes less than an hour; in others it takes many hours or all night/day. After mating, she flies away and lays her eggs on tree leaves.

Many saturniids will mate with their siblings. If you can find a wild mate, that is better, to avoid inbreeding. I had an inbred brood in which the whole brood died, apparently for no other reason.

Mating moths is the hardest part of rearing, and I'm not very experienced at it. I suggest putting the female inside a screen porch or large cage, and releasing the male in with her. There should be air flow so he can find her. The female's perfume is very powerful, and if the whole area is flooded with it, the male cannot pinpoint its source. You need a room or area that is totally free of the pheromone except for that coming from the calling female. I had to move pairs from a porch where many females had been calling to a "fresh" room before they would mate. Males will even come to an empty cage where females have been calling earlier.

Males apparently use mainly their senses of smell and touch to find the female. The male gropes her body with the claspers on the end of his abdomen until he finds where to attach them.

If you have no male, you can cage the female outdoors to attract a wild male. Use a cage of half-inch screen so that she can mate through it but not escape. (There are several other methods which I don't completely understand yet.) The only glitch is that you must recover her and her mate before daybreak, or birds will eat them! Other people who have raised moths can tell you more about how to do it successfully.

Promethea moths call and mate in late afternoon, not at night.

If your males emerge before the females, you can put them in the frij to keep them alive longer while waiting for the females to emerge. Warning - a frij at 40F is too cold; this seems to render the males incapable of normal behavior afterwards. 55F is better. Ultimately, though, if you want to be certain of getting a mating, you must have a fair number of pupae. Having several of each sex is not enough; you need enough so that there will be males and females emerging within a couple of days of each other. My guess would be about 20 pupae.

You can put the mated female in a paper bag to lay her eggs. Or use a a large plastic container, like a plastic shoebox, with paper towels on the bottom. Unfortunately, either way she will usually beat herself to a frazzle trying to fly.

Things to see:

The adult moth must escape the cocoon when it emerges. In polyphemus, the moth secretes a enzyme from its mouth area that weakens the "glue" attaching the threads together, then uses little blades on its "shoulders" to cut a hole in the silk. Luna moths make weak, thin cocoons, and do the same thing without the enzyme. Other saturniids simply push their way out; they make the outer layer of the cocoon with a hole at the head end, and the inner layer like a drawstring that can be forced open from inside. They also secrete chemicals that help the opening to expand. You can see their wet foreheads as they emerge.

It is exciting to be able to go to a place where there are wild moths and see them come in to a female you have set out.

Look at a moth under a stereo dissecting microscope, or a 10x magnifying glass, to see the beautiful scale colors.

If you have questions, or you have additional knowledge or corrections that I should incorporate into this page, please email me. Enjoy!

Liz Day beebuzz@kiva.net

ACKNOWLEDGMENTS

While raising larvae and writing this, I was greatly assisted by Eric Quinter, Valerie Passoa, Chris Conlan, Mike Soukup, Paul Weaver, and Robert Thorn. Thank you!! :-)