Citheronia regalis is a species with many common names; you may know them as the Hickory horned devil, the Royal walnut moth or the Regal moth. This species is found in the eastern half of the United States of America, Canada, and northern latitudes of Mexico. In most localities, they are a true summer species that appears from June to August. The moths appear to be velvety grey with highly contrasting dark orange veination and and pale white spots. Both males and females look similar, but are still easy to tell apart due to their size difference; the males are often half the size of females.
The life cycle of this insect is closely tied to the presence of some of their favorite plants; in the wild these are several types of Hickory (Carya sp.), sweetgum (Liquidambar sp.), walnut (Juglans sp.), staghorn sumac (Rhus typhina) and persimmon (Diospyros virginiana). These are their favorite host plants in the wild, although in captivity, the caterpillars can be raised on many more plants.
The caterpillars are one of the largest in the United States of America without a doubt; reportedly reaching lengths of 16 centimetres in some occasions. They look extremely impressive and are lime green with fluorescent yellow accents, and large orange horns on its thorarical segments. Despite their extremely large size, bright colours and threatening spines and horns, it is worth noting that the caterpillars are actually completely harmless. They are not venomous nor poisonous in any way or shape, and if one is comfortable with touching such a large insect, are completely safe to handle.
Their impressive appearance is also the reason that have also become a reasonably populair species in the pet trade in the United States of America. But even in Europe, where the insect is not native, the eggs and pupae are sometimes exchanged by hobbyists; and the insect is relatively easy to raise in captivity.
- Difficulty rating: Average (Not difficult; but basic experience with moths can be recommended)
- Rearing difficulty: 6/10 (From egg to pupa)
- Pairing difficulty: 6/10 (Archieving copulations)
- Host plants: Their favorite (and best) host plants are Hickory (Carya sp.), sweetgum (Liquidambar sp.), walnut (Juglans sp.), staghorn sumac (Rhus typhina) and persimmon (Diospyros virginiana). On top of that, the insects can be raised on privet (Ligustrum sp.), ash tree (Fraxinus sp.), sycamore (Platanus sp.), cherries (Prunus sp.), levant cotton (Gossypium herbaceum), willow (Salix), bush honeysuckle (Dierviella sp.), Lonicera (honeysuckle), smoketree (Cotinus sp.), Peruvian peppertree (Schinus molle), lilac (Syringa vulgaris), sassafras (Sassafras albidum) and more.
- Natural range: Eastern half of the United States; Canada, Mexico
- Polyphagous: yes
- Generations: Univoltine (single brooded)
- Family: Saturniidae (silkmoths)
- Pupation: Naked pupa underground
- Prefered climate: Temperate climate; warm and dry summer, cold winter
- Special notes: Not very difficult to breed; but easy to overcrowd in captivity by accident due to the sheer size of the larvae.
- Estimated wingspan: 80mm-155mm (males smaller, females very big)
- Binomial name: Citheronia regalis (Fabricius, 1793)
The eggs of Citheronia regalis are creamy yellow, and oval. They are able to hatch in 8 to 15 days, depending on the temperature (the warmer, the faster the development). On room temperature, it typically takes about two weeks time. Personally, I prefer to hatch them in petri dishes, and mist them lightly with water. Interestingly, among breeders, a myth appears to be circulating about the eggs releasing toxic or gasses fumes (??) when they hatch (weird, I know..) which suffocates the other caterpillars in plastic containers. This myth is likely due to the fact that some breeders struggle to maintain a good hatching ratio with Citheronia regalis eggs, combined with the naturally bitter smell this species produces in all life stages. Personally, I never had any issue hatching the eggs of this species, and I personally find it very hard to believe this theory.
I did notice however, that when the eggs are very close to hatching, they will become dark and later transparant (you can see the caterpillar inside!) and at this stage, they can easily dry out. Personally, I keep the yellow (undeveloped) eggs dry and do not spray them with water. But once the eggs become dark and I suspect that the caterpillars are about to hatch within 48 hours time, I begin misting them with water a lot.
As soon as the caterpillars are born, they already have their iconic spines and horns. The easiest way to raise them, is to pick them up with a soft paint brush or q-tip and place them in a plastic container that contains leaves of their favorite plants; recommended are walnut (Juglans), sweetgum (Liquidambar), hickory (Carya), sumac (Rhus), and persimmon (Diospyros virginiana) which are their favorite plants to eat in the wild, and produce some of the biggest caterpillars and moths. Alternatively they can also be raised on cherry (Prunus) and ash tree (Fraxinus) and lilac (Syringa vulgaris) with acceptable results although they may take longer to grow on these plants.
The second instar looks like a big version of the first instar, with a brown head capsule, and more orange/brown body and more elaborate spines. I prefer raising instar 1 and instar 2 in plastic boxes, but it’s safe to raise them in an open cage aswell. It is very important not to disturb caterpillars that are about to shed their skins; instar 1 of Citheronia regalis attach themselves to the surface with a silk pad for grip, as shedding their skin is complicated due to their large horns. Do not remove or displace them in this process, or it may end up failing.
Instars 1 & 2 seem to be very strong in captivity, and are tolerant to both being humid or dry. This species does like warmth (they are a summer species) so make sure not to rear them too cold; they’re comfortable around 21C-26C (lower is possible, but may make them grow more slowly)
The third instar is light chestnut brown with large, pronounced thorarical horns. In L3, it’s recommended to move them out of their plastic boxes, and allow them to free roam in cut branches of food plant
In the 4th instar, their size becomes quite respectable. And soon, they will shed their skins to the fifth instar.
Interesting to know is that fresh L5 caterpillars are grey or brown. Their green colour is something that develops over time, in the span of several days. I guess it takes them several days to produce enough green pigments.
The L5 caterpillars are gigantic! While they are easy to raise, it takes a skilled breeder to raise them to the “original” size they have in the wild. Host plant that is not optimal (such as Ligustrum) can produce smaller caterpillars and moths, that are tiny compared to wild specimens. The trick is warmth, a lot of space and food per individual caterpillar (they eat a LOT!) and little stress.
When this species wants to pupate, they become pale, almost turquoise; and burrows in the soil. In captivity, as substrate, soil can be used but also shredded paper towels and maybe vermiculite. Make sure the substrate is not extremely dry, and not too difficult for them to burrow in.
Try not to disturb them for the coming 3 weeks, and carefully check back later to harvest the fresh pupae.
The pupae are black, hard, and shiny – they are able to wriggle their abdomens.
This species is univoltine; which means they only have one generation a year. The pupae hibernate, and require a prolonged cold period that is several months long, in order to develop into moths. It’s recommended to store them in a cold basement, a fridge, or simply outdoors in winter, and forget about them until next spring. Only then, after gradually being warmed up, moths will appear.
Second brood? Some sources proclaim that this species can produce a second generation in the “deep south” (southern U.S.A states) but personally I doubt this information. Please note that doubting something is not the same as outright dismissing it – there is a chance that this information is true. But I have spoken to dozens of breeders from these regions, and none of them have actually ever observed pupae of this species producing moths the same year. Perhaps have a bimodal emergence pattern in the south that is statistically confused with them having two broods? If it is true they can have a second brood, then it must be a rare occurence (partial second generation?).
Personally, I recommend treating them as single brooded (univoltine) which they are in the majority of their geographical range; claims of a potential second brood are disputed and maybe untrue (but who knows?). It is clear these moths mainly produce one generation a year – maybe always in fact. If you know more about this species and their brood(s) in the south people contact me !
If you did everything correctly; then enjoy your moths! Citheronia regalis is not difficult to pair, although very strongly related individuals (inbreeding) may refuse to pair with their brothers/sisters in captivity. But if the stock is good and not strongly related, they easily pair if given some warmth, darkness, and airflow.
These moths do not feed, and their mouth parts are vestigial. They only live for 7 to about 16 days ; during this time they mate – and after the female has deposited all her eggs – they die. The females of this species can have a very large wingspan!
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Citations: Coppens, B. (2021); Written by Bart Coppens; based on a real life breeding experience [for citations in literature and publications]
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