Automeris io — “Io moth”

Automeris io, the io moth, is a very charming little silkmoth from America. It is found from Mexico, to most of the United States and Canada. Their most prominent feature are the brightly coloured and conspicuous eyespots on their hindwings, that give onlookers the impression they are being watched. It is also perhaps one of the most widespread and common Saturniidae species in North America because of their adaptability; Automeris io can survive in a broader range of climates and host plants. The females are brown and the males are bright yellow.

One female (brown) and three males (yellow) of a Automeris io 

Automeris io is found in a variety of habitats such as suburban areas, decidous forests, shrubbery in grasslands; very polyphagous and is able to survive in a wide array of habitats. The females passively wait for males to arrive that are willing to copulate with her. This species is considered nocturnal, although their activity actually starts in the late evening. After pairing the female becomes slightly more active, and she will look for a suitable place to deposit 50 to 250 pale white, oval eggs. Fertile eggs develop a clear black dot (micropyle). Moths do not feed and are short lived (7 to 14 days). The eggs hatch in 2 to 3 weeks time and the social larvae will stay together after hatching, feeding from various trees, grasses and shrubbery. The caterpillars are green to yellow and have venomous spines that can deliver a painful sting upon skin contact. While social at first, as the caterpillars grow older they will become more solitary.  When fully grown, caterpillars spin papery brown cocoons between plant leaves, in crevices or forest floor litter. Depending on the season and geographical location, the cocoons will decide to hatch in a few months or overwinter. In the most southern warm localities this species does not overwinter at all and has 3 to 4 generations in one year, while the environment in the most northern populations in cold localities only permits them to have one (1) generation a year, always overwintering as cocoons until the next spring.

Automeris io caterpillar – final instar 

In captivity Automeris io is easy to raise, although I don’t consider it a species for beginners. The caterpillars can be unpredictable when it comes to food preference which requires some flexibility from breeders.

  • Difficulty rating:Average – not difficult to breed, but you will need some basic experience with Lepidoptera.
  • Rearing difficulty: 6/10 (From egg to pupa)
  • Pairing difficulty: 4/10 (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); and many more species of deciduous trees and shrubs, more than could be possibly compiled into one list. The food preference of the larvae may vary regionally througout their expansive range.
  • Natural range: Canada; United States (Georgia, Florida,  Montana, North Dakota, South Dakota, Nebraska, Colorado, New Mexico, Texas, Utah); arguably Central America (Mexico, Costa Rica) although it is subject of discussion if the variations encountered there are subspecies of io or their own species. (neomexicana, draudtiana, potosiana, siri, et cetera).
  • 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 range 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.
  • Special notes:  From my experience, Automeris  io from different geographical locations will have different tastes in host plants. This has not been confirmed scientifically,  it’s just a breeders tip, but for example, one strain will love to eat Ligustrum and another strain will rather starve to death than take a bite of this plant. To raise them, use their local host plants. Every microclimate has different food plants and it seems the moths slightly adapt to this. Great plants to use are oak (Quercus), bird cherry (Prunus serotina). It’s possible to raise them on bramble (Rubus) and privet (Ligustrum) too but, not all bloodlines will eat these plants.
  • Estimated wingspan: 45mm-85mm – males smaller than females

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. They are often deposited 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 wait for their brothers and sisters to hatch, and begin to travel in groups and settle on a leaf that they will start feeding on about 12 to 24 hours after hatching. In captivity, the eggs are easily hatched on room temperature in a petri dish or plastic box.

Automeris io eggs (notice black dots indicating fertility)

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. 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.

Automeris io L1 on Ligustrum ovalifolium

Automeris L1 on Ligustrum ovalifolium

The first instar of Automeris io is yellow(ish) to brown(ish). The second instar is more pale yellow, and the third instar grey(ish). The first three instars can be raised in boxes, if given enough fresh food and space. Since this species is social, they grow much better if kept in bigger groups.

Automeris io L2 feeding on hawthorn (Crataegus) 

Automeris io L2/L3 on Salix and Ligustrum

From the third instar and beyond, how you should take care of the larvae changes. Now, they want ventilation, not closed airtight plastic boxes. Place them in a fauna box, or plastic box that has the lid removed and/or replaced with netting; make sure they cannot escape. Automeris io larvae are able to chew holes in some types of netting and escape, it’s better if the walls are slippery and the larvae cannot climb up to escape the container.

Automeris io  L4 and L3

In instar 4 and 5, the larvae lose their social behaviours and disperse to live a 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, they suddenly require more space per caterpillar than they did when they were social (gregarious). Despite that, the species is still very resistant to living in high densities.

Automeris io L4 on Prunus laurocerasus

The 5th instar is 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 2-3 months time, potentially faster if kept hot.

The caterpillars of Automeris io are venomous, and touching them may inflict a sting. Despite this, the sting is very mild, and not considered to be very harmful. The stinging sensation quickly dissapears after 5 to 10 minutes, leaving sore or itchy skin – it’s almost the same as a stinging nettle.  The only people who should be careful with the caterpillars are people with allergies. However, the sting of Automeris io is quite mild compared to that of some tropical species of Automeris, that can be more fierce. Despite this, there is no need to cuddle or touch them (I’m a bad role model).

Automeris io L5 on Prunus laurocerasus

Automeris io L5 on Prunus laurocerasus

Automeris io L5

When fully grown, the larva will spin a thin papery cocoon; usually among the leaves of the food plant, or litter on the floor. 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.

The cocoons of Automeris io do not seem to diapause in captivity if kept warm. I have succesfully bred this species in 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 undeniably use other cues to overwinter such as day length and light intensity, it seems that no matter what, diapause is 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 want to overwinter them, store them cold. In the wild, they can survive cold temperatures up to -20C in winter. Despite that it is not recommended to continuously expose them to frost, and ideally they are overwintered outdoors in temperate areas, or in a fridge around 5C.  Typically the moths will begin to develop if pupae are kept warm.

Automeris io cocoon

Automeris io cocoon

The adults of Automeris io are simply beautiful; the males are bright  yellow (or curiously, sometimes orange in Florida, Automeris io var. lilith),  very  fluffy and decorated with smaller brown markings. Females  are  bigger  than the  males, and brown in colour. Adults live for 4 to 14 days; males live a shorter time than females.

Automeris io male

Automeris io female

Rearing Automeris moths can be tricky, but pairing them is very easy. This genus seems to be one of the easiest to pair silkmoths in captivity. Although they can confuse breeders: most silkmoths remain attached together after copulating for 12 to 24 hours. This makes it obvious to the breeder that a pairing happened the previous night, by observing how the males and females are connected by their abdomens post-copulation.

Automeris io however, only pairs very briefly, for 30 to 60 minutes, and after pairing the male often quickly leaves; perhaps to pair with multiple other females per night(?). However, a 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.

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. Then, leave them alone in the dark and they should easily pair.

The copula of Automeris io is hard to observe, and tends to last only 30-60 minutes. Blink and you’ll miss it. Pairing happens at dusk and night.

A few days after pairing, females will begin to deposit many eggs. Females lay 50 to 300 eggs, depending on their health and size (big, healthy females lay more). After a generation or two, it’s easy to have over 1000 eggs!

Automeris io brood producing hundreds and hundreds of fertile eggs(!)

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!

Automeris io adults

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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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