Citheronia regalis: Do's and Don'ts

Some questions arrived in September of 2007 so I have updated this article with the questions and answers at bottom of page.

The spectactular size and "weaponry" of Hickory Horned-Devil larvae can't help but impress all those who rear them. For such a monstrous larvae (often exceed six inches), they are relatively easy to rear. Final instar larvae are most often green, sometimes taking on a bluish hue prior to pupation. This article presents the "Do's and Don'ts" for a successful rearing program.

Larva developing inside the egg, courtesy of Louis Dawson.

Louise Dawson writes, "The Citheronia ova are so cool! I can clearly see the developing larva inside and even see them move through my 20X fieldscope. They look like little light yellowish donuts inside with dark heads."

My experience has been that incubation takes about ten days, and the dark heads will become visible through the eggshell at around the seventh day. This seems to be true of many of the large Ceratocampinae.

"Do's":
1) Divide up your regalis eggs so that you only have a few eggs in a good sized hatching container.

"Don'ts":
1) Don't put foliage in with unhatched eggs.
2) Don't "put all your eggs in one basket."

Both my father and I have seen Ceratocampinae eggs develop nicely, with visible larvae forming up, only to have the eggs go unhatched. Something happens to the developing larvae just before emergence. Others report this same experience.

We have long known not to put foliage in with unhatched eggs in a closed container. The results are usually disastrous and this applies not only to Ceratocampinae eggs. Either the moisture or the Carbon Dioxide or other gases from the foliage or a combination apparently suffocates the developing larva inside the eggshell.

The larva may need a good supply of oxygen at this critical time and the coating of condensate that forms on the eggs in such cases may well block the transfer of Oxygen through the micropyle (little breathing hole). It is also possible that the Carbon Dioxide buildup from the foliage simply smothers the eggs.

I recently received two dozen regalis eggs. I divided them up into groups of four-eggs-each to quart sized zip-loc plastic tubs. The lids were on tight, no airholes. Unhatched eggs were carefully lifted (with a spoon) to new containers before foliage (Rhus typhina; Staghorn sumac) was introduced to the hatchlings. All twenty-four eggs hatched.

Anyone, who has ever opened a closed container with numerous regalis hatchlings, has probably noticed a distinct odor. These "emergence" fumes (in a closed container) may well have the same effect on unhatched eggs that foliage does. The fumes may be toxic in themselves or may form a condensate that smothers unhatched eggs.

Jeff Shumacher writes, "I just recently received some regalis ova from you (my father). I have a problem: Of the dozen ova I got, only six of them hatched. The others looked like they were developing, but just when it looked like they should be ready to hatch, they died. Of the six that hatched only two of them started eating. I had them on black walnut. Two years ago I had a mating of regalis and the same thing happened to almost all of the ova. I can't figure out what I could have done to cause this to happen."

Jeff indicated he had not put foliage in with unhatched eggs, so I suspect emergent fumes may have "done in" the unhatched eggs.

It is also a good idea to offer hatchlings a variety of leaves from the known host plants list. My father has documented a case where luna hatchlings would not accept the same foliage (willow) which their mother had been fed. My father usually uses willow for his regalis, but sweetgum and sumac have also served well. Hickories, walnuts, gums also work well.

Below is a list of recognized foodplants.

"Do's":
1) Offer a couple of potential hosts, but only ones for which you have sufficient access to get the brood through.

"Don'ts":
1) Try to rely on a single host; it is possible that the larva will not accept foliage of parents.
2) Choose a host that is in short supply or difficult to access.

If you run out of starter host part way through the season, you can try offering another host. Sometimes larvae will switch without coaxing. If the larvae seem reluctant to switch, you can try an old trick: Chop up a fresh leave of the original foliage and rub the juices all over your fingers and then rub juices onto new potential host. Sometimes this will get otherwise reluctant larvae started; once they get started, they will usually continue feeding on the new host.

"Do's":
1) Be patient with hatchlings. They have tiny bellies and have literally eaten their way out of the eggshell. It is not uncommon for them to climb along the side of the container and arrange themselves so that the top of body looks limp and is bent downward toward the anal claspers. In this typical resting posture, they resemble bird droppings, and the pose may simply be a camouflage mechanism.

2) Gently brush or lift them back onto foliage with your fingertip or a spoon if they haven't returned after a couple of hours.

Even after they have started feeding, they frequently leave the foliage, and this can be most annoying in a sleeve where they offer themselves up to stinkbug predation by hanging on the sleeve.

"Don'ts":
Immediately assume they are going to starve to death and won't accept what you have offered.

If you are offering a variety from the above list, they will probably settle on something. Sometimes they just take little nibbles and then move on. Tiny poop in the bottom of sleeve or container indicates something is eating!

Once larvae have started feeding the hard part is probably over for this species. They seem quite resistant to disease.

"Don'ts":
Avoid overcrowding: Despite regalis' resistance to disease, overcrowding is never a good idea for any species. Too many larvae in a single sleeve can also result in a "healthy supply" of foliage disappearing overnight. A day or so without food or the water incorporated in it, can severely stress larvae.

Caterpillars can overheat in a sleeve without some protection from foliage. It is remarkable how much heat energy is actually taken in by foliage. If you burn firewood for heat, all that heat energy in the wood was taken in by leaves.

I suspect there is also chance for wounds from pointed structures on forelegs if caterpillars start crawling over each other!

"Do's":
Empty frass from sleeves frequently, especially before rain (avoids a soggy mess).

Check on nearly mature larvae regularly. Caterpillars have strong mandibles and many can actualy chew holes through various sleeve materials to escape, either looking for food or a place to pupate.

When you see larvae crawling around at the bottom of the sleeve or rearing cage/container, it is time to remove them to pupation chambers. Sometimes larvae take on a slightly bluish tinge when ready to pupate.

I treat all of the earth pupators (Ceratocampinae, Sphingidae) the same way. I use dark plastic buckets:
indoors to avoid overheating in direct sunlight and provide warmth during fall nights;
covered to avoid caterpillar escapees from startling other members of the household;
and
lined with loose paper towelling so larvae can "descend" to a darker region.

The larvae are simply placed inside the buckets or smaller individual chambers and allowed to "sweat" and shrivel considerably. This is natural. Legs will get stumpy and larvae should pupate within three to five days. They may crawl around for a day before settling to bottom of container. Darkness helps!

Considerable brown fluid was discharged by larvae into tubs and this was poured off as it accumulated.

In the image above, I have placed a larva about to pupate in with a pupa and discarded skin. You can see the shriveled nature of the larva. This is typical of all the earth pupators, but not all shrink as much or discharge as much fluid as regalis.

Jeff Schumacher writes: "I know that I've read that some people have had trouble getting regalis to pupate successfully. I've found a method that seems to work quite well. I don't know if you've ever heard of Omaha steaks, but when you order something from them, they send it in a styrofoam cooler packed in dry ice.

What I've done is use the cooler as a pupating box. I put a layer of moist paper toweling in the bottom and a few layers of newspaper on top of that, and then another layer of moist paper toweling on top of that. The regalis larvae burrow to the bottom and pupate. I've found this method to be very sucessful.

I hope that this information is helpful.

"Don'ts":
Newly formed pupae are extremely soft and should not be moved/touched for at least several days to give pupal shell a chance to harden.

It's not good to have larvae crawling over fresh pupae either, so you might want to consider smaller individual chambers for larvae that are ready to pupate. My father has used the individual chambers in a fishing tackle box with good success.

Once the pupae have hardened, they can be cared for as per these instructions from Don Oehlke:

"Pupae can be kept wrapped to keep moisture constant ALL THE WAY to eclosure." (Wrapping consists of taking the hardened pupae and literally wrapping them in a piece of toilet tissue or regular hand tissue paper. Don't make the wrap too tight (taut); placing the pupa at one edge of the tissue and then gently rolling will have the desired effect.)

(In the fall, the wrapped pupae can be placed in storage tubs. A light misting of the tissue will help to conserve moisture and simulate the humidity encountered in the natural subterranean chambers.)

(Check your storage containers once a month throughout the winter and mist wraps if necessary. This monthly check probaly also serves to freshen air in otherwise airtight containers. I store my Sphingidae and Ceratocampinae in ziploc plastic tubs in fridge crisper. See Overwintering Pupae article.)

In the spring, pupae can come out of storage and should be placed in an emergence cage:

"Sprita with water not less than once a day out of direct sun. Temps should be 70 to 85F with air circulation. As of June 1, they should be wet down twice per day or more if surrounding air is hot and arid. Mold will not occur on live pupa. They can be teased to wiggle by running a fingernail down the abdominal segments. Remember desiccation is the worst enemy also birds and rodents. NO HIGH HEAT NO DIRECT SUN."

"They should eclose between 6/15 and 7/15 depending upon warm temperatures. Do not attempt incubation in air conditioning (they may not emerge without warmer temps.) You can place a paper towel on top of covered pupa and make sure you keep it damp and read Bills' instructions. I have kept these live for nine months--the rest is up to you!"

Other articles you should read include the following:
Earth Pupators
Overwintering Cocoons and Pupae
An Emergence cage for Citheronia regalis

The instructions vary slighty from article to article as my father, Scott Smith and I all use slightly different techniques. General principles, however, remain the same.

There may be two broods annually in the extreme south, but generally regalis is a univoltine (single brood) species. Approximating natural outdoor conditions for winter storage for your specific area will probably help with synchronization with natural flight. A hard freeze, however, is not necessary.

Although regalis mate readily in captivity, there seems to be some reluctance for siblings to mate. If you want pairings, you need to be in an area where there are native populations so wild males can be called in, or you need to have pupae from two different brood stocks.

Citheronia regalis on sweetgum, courtesy of Don Adams.

On September 1, 2007, I received a series of questions. The questions and my answers are below.

"Bill.

All of our Citheronia have done quite well and are 5th instars. We have not dealt with burrowers in the past except when we have purchased them as pupae. We have read your website with your advice that you have had good luck putting them in a dark box with paper toweling however I am hoping to clarify about your technique. First of all, how do you know when to place them in the box? Do they change color as some larvae do? We have ours as 2-3 per container and all are quite large so simply having intestinal droppings in the container might not indicate who was ready to pupate. Do they wander off food and for how long before pupating (in other words, how long do we have? If I am at work all day and my son is at school, could we have problems?). Also, do you simply layer the paper towelling or do you crumple it? Once they've pupated, how do you care for them (i.e., do they need to be kept moist? I always worry about mold and mildew and am wondering about your solution). Sorry to bother you with all of these questions; we have 100% success with these larvae up until this point and would love to do our best for them."

1) First of all, how do you know when to place them in the box?
I use sandwich sized ziploc plastic tubs for pupating earth pupators. You can place them anywhere in the tub.

2) Do they change color as some larvae do?
Sometimes they take on a bluish cast; other times there is no apparent change in colour.

3) Do they wander off food and for how long before pupating (in other words, how long do we have?
Yes, they will stop eating and will begin crawling around bottom of container. You have a couple of days, but I usualy check my containers every morning and move, to pupation tubs, the ones that have left foliage.

4) If I am at work all day and Noah is at school, could we have problems?
No problem if you check every morning and just move those that are crawling around bottom of rearing container.

5) Also, do you simply layer the paper towelling or do you crumple it?
I fold the paper towel in half once, and then I fold it in half again, without a tight crese either time, and then just lay the towel loosely in bottom of container.

6) Once they've pupated how do you care for them (i.e., do they need to be kept moist?
They probably won't pupate until they have been in the plastic tubs for 4-6 days. There wil be considerable shrinkage (due to sweating) and the paper towel will become very moist. First time you watch this process you might think the caterpillars are dying. Their legs will become quite stumpy. I let them sit in tubs for a week or two, even longer sometimes before doing anything. It is not good to handle them for several days after pupation as pupal shells will be very soft.

I stil have regalis pupae and Eacles imperialis pini pupae sitting in original pupation tubs (sometimes put two or three larvae in a single tub) on shelf in kitchen. I will put them in cold storage late September early October by wrapping each pupa individually in a single two ply sheet of toilet tissue. I moisten my thumb and index finger slightly and twist the head end and tail end of the toilet tissue wrap to hold it in place, sort of like the twisted ends of salt water toffee wrappers.

For storage, I place a fresh, clean, no color no scent paper towel folded as above on bottom of another fresh clean tub. Put a couple of drips of water on the paper towel, and then lay the toilet tissue wrapped pupae on top of the paper towel. I just about fill the tub with pupae and then place another folded paper towel on top. Add a drip or two of water and then put lid on tight, no airholes, and put them in fridge crisper for winter.

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