Automeris io, the io moth, is a very charming little silkmoth species found on the American continent; it is widespread and found in southern Canada, the eastern U.S.A, and northern Mexico. Their most noteworthy features are the bright eyespots that they display when they are startled and also their mildly venomous caterpillars. It is a somewhat adaptable species that can use a wide variety of host plants and that may occur in many habitats that have enough woody plants or shrubs to support them; from woodlands to meadows to scrublands, orchards and in some cases even parks and gardens. Do not be surprised to encounter them in urban spaces! The larvae of this moth have venomous spines and will give those who touch them a good scare; despite this information they are generally considered to be harmless, and the pain generally subsides within 5-10 minutes. The sensation is often described to be similar to the sting of a stinging nettle (Urtica sp).

It is the most northern species of Automeris; the genus contains about 124(!) species of which the majority are found in the tropical to subtropical regions of South and Central- America. Only a handful of species however are also found beyond Mexico into United States of America. Among these species, Automeris io is the most common and widespread species with the most northernly latitude. It is found from South-East Canada (around Ottawa, Montreal, Winnipeg) into most of the eastern United States of America where it seems very widespread; in the U.S.A it is found almost anywhere from the east-coast towards the Rocky Mountains, which appear to be a geographical barrier for the species as they do not naturally occur on the western side of the Rocky Mountains and seem restricted to the eastern side. Beyond that, it is found into northern Mexico.

If we move southwards from Mexico there are populations of similar looking moths that extend from Mexico all the way into Guatemala, Honduras, El Salvador, Nicaragua and northern Costa Rica but it is unclear if these are truly Automeris io or if they are different yet similar looking species, such as the almost identical looking Automeris draudtiana (the taxonomy needs more work, but there are indications that beyond Mexico, they might not classify as true Automeris io anymore). Some of these are former subspecies of Automeris io now potentially elevated to full species status.

The species is also often reared by moth-enthusiasts; it is known to be somewhat beginner friendly and easy to breed. My website contains information about the ecology and life history of species, but also breeding/rearing information!

The species is notable for having a rather broad appetite. Caterpillars have been found eating some of the following plants: cherry (Prunus), redbud (Cercis), willow (Salix), Wisteria, Sassafras, currant (Ribes), Hibiscus, hickory (Carya), poplar (Populus), pear (Pyrus), limetree (Tilia), elm (Ulmus), fishpoison tree (Piscidia piscipula), oaks (Quercus),  blackberry (Rubus), maple (Acer), birch (Betula), tuliptree (Liriodendron), Gleditsia, privet (Ligustrum), ash (Fraxinus), hazel (Corylus), beech (Fagus), corn (Zea mays), bamboo (many Poaceae), coral bean (Erythrina), hop (Humulus lupulus), walnut (Juglans), sweetgum (Liquidambar), black locust (Robinia), mesquite (Prosopis), hackberry (Celtis), privet (Ligustrum) and potentially many more. While not picky, it does seem to have an appetite for in particular for woody plants from the legume- (Fabaceae) and rose/cherry- (Rosaceae) plant families, although it clearly also has many host plants beyond these plant families.

The males are bright yellow, and females brown. When startled, the moths might attempt to display their hindwings and wiggle around on the floor. If that fails, they simply fly away. The species is nocturnal, and males and females pair in darkness (after sundown to midnight it seems). The pairing can be very brief, I have personally observed males mating with females in captivity and then leaving her within 15-30 minutes. In resting position, the moth is well camouflaged and looks like a dead leaf. As with most Saturniidae they have a short lifespan and do not feed (5-14 days generally).

It appears the species has a faculative diapause; which means that if they are kept warm, the pupae tend to develop into moths quickly. Whereas other moth species might produce one single (obligate) brood a year as their cocoons or eggs always hibernate, Automeris io is more adaptable. This also explains why the species often produces only one (1) brood a year in northern latitudes (such as Canada) whereas in southern locations (such as Florida) they can produce 3-4 broods in one year. In captivity, if kept warm enough, they can often be bred almost continuously; keeping the cocoons cold is simply what appears to induce hibernation in a lot of cases.

• Difficulty rating: Simple – not difficult to breed, but you will probably need a little bit of basic knowledge and experience.
• Rearing difficulty: 4.5/10 (From egg to pupa)
• Pairing difficulty: 2/10 (Archieving copulations)
• Host plants: Extremely polyphagous, with over hundreds recorded food plants. Favorites include cherry (Prunus), redbud (Cercis), willow (Salix), Wisteria, Sassafras, currant (Ribes), Hibiscus but they have also been recorded on hickory (Carya), poplar (Populus), pear (Pyrus), limetree (Tilia), elm (Ulmus), fishpoison tree (Piscidia piscipula), oaks (Quercus),  blackberry (Rubus), maple (Acer), birch (Betula), tuliptree (Liriodendron), Gleditsia, privet (Ligustrum), ash (Fraxinus), hazel (Corylus), beech (Fagus), corn (Zea mays), bamboo (many Poaceae), coral bean (Erythrina), hop (Humulus lupulus), walnut (Juglans), sweetgum (Liquidambar), black locust (Robinia), mesquite (Prosopis), hackberry (Celtis), privet (Ligustrum) and potentially many more.
• Natural range: Canada (near Ottawa, Montreal, Winnipeg- southeast Canada) United States of America (Georgia, Florida,  Montana, North Dakota, South Dakota, Nebraska, Colorado, New Mexico, Texas, Utah); northern Mexico. It is still a subject of discussion whether or not the populations of similar looking moths that are found south of Mexico in Central America (Nicaragua, Honduras Guatemala, Costa Rica) can be classified as true Automeris io; they might be similar looking but different species (neomexicana, draudtiana, potosiana, siri, et cetera). It is not unusual for moths in the genus Automeris to have species complexes with many similar cryptic sister species.
• Polyphagous:Yes, very
• Generations: Multivoltine – continuously brooded if kept warm, but can overwinter if cocoons are stored cold. This species overwinters in the cocoon stage. Although if kept warm, the cocoons will always hatch; their emergence is inhibited by temperatures. This is evident in warm (sub)tropical climates where they can be continuously brooded.
• Family: Saturniidae (silkmoths)
• Pupation: Cocoon (silk encasing)
• Prefered climate: Temperate; although they are found in a big variety of microclimates, from  humid (sub)tropical regions such as Florida to hot and dry regions such as Texas and Mexico – but also much further up north up to Canada and northern states such as Montana, where the climate is significantly colder and experiences very cold winters with persistent freezing. It seems adaptable and tolerant.
• Special notes:  From my experience, Automeris  io from different geographical locations might have different tastes in host plants. This has not been confirmed scientifically,  it’s just an anecdotal breeding tip from me, the author of this website. However, for example, one strain will love to eat Ligustrum and another strain would rather starve to death instead of taking a single take a bite from this plant. Yes, the species is polyphagouys, but not every bloodline seems to like every type of food plant. I am not sure why this is; food for thought, perhaps? In order to raise them, perhaps, use their local host plants, especially if you know the geographical origin of the livestock. Great plants to use are generally oak (Quercus), bird cherry (Prunus serotina), and willows (Salix).
• Estimated wingspan: 45mm-85mm – males smaller than females
• Binomial name: Automeris io (Fabricius, 1775)

Generally speaking, Automeris io is easy to raise and/or breed and will generally be no challenge for more experienced moth breeders. I am not sure if I would recommend them for total beginners (maybe not that easy) but if you’ve bred more than a few moth species in your life, then you are probably capable of breeding Automeris io. The main challenge is keeping the larvae comfortable in terms of humidity, and handling them the right way.

Eggs: The eggs of Automeris io are oval, creamy yellow with a white band that runs along the side. If the eggs are fertile, they have a visible black dot (micropyle). Infertile eggs have a grey/green dot. Note: the black dot only becomes visible a few days after being laid, and not immediately. The female often deposits them in clusters/rows, with the micropyle facing upwards. Automeris io eggs hatch in 2 to 3 weeks time. After hatching, the caterpillars will not eat right away; instead they tend to wait for their brothers and sisters to hatch, and only once enough of their siblings have managed to gather, they start to travel in small groups and finally settle on a leaf that they will start feeding on about 12 to 36 hours after hatching. In captivity, the eggs are easily hatched on room temperature in a petri dish or plastic box.

The first instar should be kept in a dry container, that is also airtight, without much ventilation, as the babies are prone to dessication. Despite that, they don’t like overly humid containers with a lot of condensation. I imagine this sounds like a paradox; do they want to be humid or not? It’s more about keeping the relative humidity (the air) high while avoiding wet conditions (they generally resent condensation and/or wetness).

Paper towels on the bottom of your container, or opening the lid for about one hour per day to ventilate it (and then close it!) will also help keep the humidity down, as does not adding too much food plant (leaves evaporate water). Automeris io is very polyphagous and can be raised on many plants, personally I had succes with Quercus, Prunus, Ligustrum, and Salix.

The first instars of Automeris io are more or less brown. The first three instars can be raised in boxes, if given enough fresh food and space. Be geneous with space, if you can. Since this species is social, they grow much better if kept in bigger groups (here is your excuse to obtain more eggs!), and to me, young larvae seem more comfortable in groups of 20+ individuals.

From the third instar and beyond how you should keep the larvae changes a little bit. Now they will want more ventilation (fresh air, not stuffy conditions!) instead of closed airtight plastic boxes. Suitable are large fauna boxes, plastic box that have the lid removed (cover it with mosquito netting instead), or simply in open pop-up insect cages, on cut/bottled food plant. Make sure they cannot escape! Automeris io larvae are able to chew holes in some types of netting and escape it seems, especially if they run out food; they seem to chew on anything if they are ‘hangry’.

Instar 4 is often silvery greyish, to light green. Instar 5 is often green (and more rarely yellow). In instar 4 and 5, the larvae slowly lose their social behaviours and disperse to live a more solitary lifestyle. They stop living in groups and now want more space for themselves. Make sure not to overcrowd them! If a species goes from social to solitary, this is your cue that they will demand more personal space per individual caterpillar compared to when they were social (gregarious). Despite this fact, the species is still more tolerant of being reared in high density setups compared to most other silkmoths.

Once they hit the 5th and final instar, they become bright green (or more rarely, only from southern populations, yellow!) with a red and white stripe that runs along their bodies. The caterpillars become fully grown in about 2 to 3 months time (7 to 13 weeks), potentially faster if kept warmer. If kept cooler, they tend to be slower than the average Saturniidae species (which is not necessarily bad for them; it’s simply just slower).

Toxicity: The caterpillars of Automeris io are venomous, and touching them may indeed inflict a sting. The sting however, is very mild and generally not considered to be very harmful, and rarely leaves any long-term health effects. The stinging sensation quickly dissapears after 5 to 10 minutes, leaving a mostly sore or itchy skin – it’s almost the same as a stinging nettle.  The feeling is described as a somewhat hot, electric and also itchy feeling. The only people who should be careful with the caterpillars are people with allergies, or those who are immunocompromised in any way. People who get stung by the larvae unsuspectingly can have a stronger emotional or physical reaction simply due to being caught off-guard and by suprise (there is a psychosomatic element to pain!). Still, make sure you are comfortable with this fact before rearing Automeris io. The sting is however quite easy to avoid, by simply not directly handling or grabbing the larvae; or rather just buy a thick pair of gloves. Do keep in mind that when they sense movement around them, sometimes the caterpillars will curl up in a ball and drop themselves to the floor(!) like a little hedgehog or porcupine in some cases. This might cause some of the falling larvae to bump into your arms and sting you.

Instar 1 to 4 barely seem to sting; I am not sure if their spines are not functional when they are younger, or if they are simply mechanically too small to penetrate human skin at that point (perhaps a combination of both). It’s generally instar 5 that tends to sting me.

When fully grown, the larva will spin a thin papery cocoon; usually among the leaves of the food plant or on the floor (in leaf litter). Before spinning cocoons, the caterpillars will wander for a long time, up to a full day, before choosing the perfect place to make a cocoon, sometimes quite far away from the host plants. Cocoons are often recorded in leaf litter on the forest floor, on tree bark, or between the leaves of the host plant. In captivity, you could provide them with shredded paper towel or even dry leaves on the floor so they can spin cocoons here. This is optional however. Most of them are happy to spin within the foliage of their food plant. Sometimes the cocoons are well-hidden among the leaves; make sure not to discard any old food plant without inspecting it.

The cocoons of Automeris io do not seem to diapause in captivity if kept warm. I have succesfully bred this species for multiple generations through the year, even in winter – despite livestock coming from places like Canada, where they only have one generation per year in the wild. While they might undeniably use other cues to start hibernation such as day length and light intensity, it seems that no matter what, diapause can be broken if they are kept warm continuously – unlike other silkmoths from North America that often need to experience a cold winter in order to break diapause (obligate diapause). The diapause of Automeris io appears to be mainly facultative.

If you do want to overwinter them, store them cold. In the wild, they can survive cold temperatures up to -20C in winter (I definitely don’t recommend doing that in captivity however; in nature the cocoons are hidden in isolated spots such as leaf litter). Still, a temperature of 5C-10C might suppress the development of the pupae for several months. It is possible to hibernate the cocoons outdoors, if you live in a place that has any semblance of winter. Even frost is no problem! Make sure to ‘pack’ the cocoons well; insulate / isolate them well by wrapping them in towels, burying them in vermiculite, or even burying them in a thick layer of leaf litter, and then placing them inside a plastic container that you hide in your garden shed, or even under some bushes/vegetation (make sure they are not exposed to full sunlight, or rain if the container is not watertight).

It is also possible to ‘skip’ hibernation by keeping the cocoons warm however. I do recommend following your local seasons if you can, assuming that you live in a temperate climate. While it is possible to rear the species indoors in winter on certain evergreen food plants (such as Prunus laurocerasus) it can result in significantly smaller individuals due to the worse food quality; even evergreen plants tend to have much less nutrients and water content in winter (they generally withdraw them into their root systems). When reared on deciduous plants they generally produce bigger and healthier adults compared to evergreen food options.

Once you have your moths, congratulations! The adults of Automeris io are simply beautiful; the males are generally bright  yellow (or curiously, sometimes orange, such as the orange colour form that occurs in Florida, Automeris io var. lilith). It is worth rearing this species from diverse geographical locations; indeed there can be subtle differences between populations. Such as the desert form (or now even subspecies), Automeris io ssp. neomexicana which can have ‘tan’, orange-brownish males, or very pale yellow ones.

Rearing is the hardest part (it’s not even hard, but it’s the hardest part). Pairing them should be very easy. Although they can confuse moth-breeders: most silkmoths remain attached (coupled) to eachother after copulating for 12 to 24 hours. This makes it obvious to the breeder that a pairing has indeed ocurred the previous night, by simply observing how the number of pairs that are connected by their abdomens post-copulation.

Automeris io however, only pairs very briefly, for about 15 to 60 minutes, and after pairing the male often tends to quickly leave, perhaps in order to pair with multiple other females per night(?). Probably but who knows! However the fact remains that the pairing of Automeris io is hard to observe and photograph, unless you have the time to babysit them and check them every hour through the night. I have managed to breed the species several times, but I’ve only managed to photograph the actual pairing a few times.

To pair Automeris io, place them in well ventilated cages that have airflow (made of netting, gauze, or very narrow chicken wire); the cage walls should have enough grip for them to climb on. Place 1-2 females per cage and 2-4 males. They prefer warmer nights but they are very much capable of pairing in cooler conditions also (anything from 12C to 30C probably works). Then, leave them alone in the dark and they should easily pair.

A few days after pairing, females will begin to deposit many eggs. Females can lay around 50 to 200 eggs or so, depending on their health and size (big, healthy females lay more).

Thanks for reading my breeding experience of Automeris io. Stay tuned; many more caresheets are coming in the future, and this website is updated every year. Thanks for all your feedback and sponsorships, without you this would be impossible! If you are hungry for more moth knowledge, I have hundreds of pages that are constantly being rewritten/modernised!

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Citations: Coppens, B. (2019); Written by Bart Coppens; based on a real life breeding experience [for citations in literature and publications] 

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