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Automeris io

What do they look like?

Adult Io moths are considered medium to large-sized moths, with a wingspan of 5 to 9 cm. In this species, males and females have different wing colorations. Male forewings are usually bright yellow, while females have dark yellow or brown forewings. Females may also have larger, more pointed forewings. Both males and females have large spots that look like eyes on their hindwings; these eyespots are black or blue, with a gray or bluish iris around a white center. Eyespots are often larger and rounder in females than in males. Adults are likely polymorphic, meaning that individual moths of this species may have different colors. Io moths found in the south tend to have reddish-brown forewings, while others can also be orange-brown or purple-brown. Young caterpillars are brown, yellow, or dull orange, and are 3 to 4 mm in length when they first hatch. Older caterpillars are bright green, with 2 stripes down their sides, a red one on top and a white stripe just below. They can grow to 3 to 5 cm in length. These caterpillars are covered in branched spines. Eggs are oval with a flat top. They are white when they are first laid, with a few yellow spots on the top and sides. After a few days, the top spot changes to black, and the side spots become tint orange as the larvae develops. (Borror and White, 1970; Hossler, et al., 2008; Manley, 1978; Manley, 1993; Peterson, 1962; Russi, et al., 1973; Tuskes, et al., 1996)

  • Sexual Dimorphism
  • sexes colored or patterned differently
  • male more colorful
  • Range wingspan
    5 to 9 cm
    1.97 to 3.54 in

Where do they live?

Io moths (Automeris io) are native to the Nearctic region. They are found throughout the eastern half of the United States, as far west as Utah, Colorado, and Texas. They are found in Canada, as far north as Quebec, Ontario, and southern Manitoba. They are also found in eastern Mexico and Costa Rica, in the northernmost part of the Neotropical region. (Hossler, et al., 2008; Tuskes, et al., 1996)

What kind of habitat do they need?

Io moths are a temperate species, and can be found in many different habitats, including deciduous woodlands, forests, meadows, orchards, parks, and backyards. Caterpillars can be found feeding on leaves, and usually spin their cocoons in leaf litter on the ground or in crevices among rocks or wood. (Hossler, et al., 2008; Tuskes, et al., 1996)

How do they grow?

Adults emerge from their cocoon during late morning or early afternoon in the warm, summer months. They remain in place until evening, while their wings open. They find mates, and females lay eggs on plant leaves. After about 10 days, the eggs hatch. All eggs hatch within 1 to 3 days of each other; they do not leave until all have emerged. Larvae, also known as caterpillars, go through five stages called instars, which takes about 4 weeks. Caterpillars eat continuously before becoming pupae and spinning cocoons. Cocoons take about 7 to 10 days to fully harden and form, and even then they are very thin and easy to damage. Depending on the temperature and amount of daylight, pupae either emerge from their cocoon as adult moths within a few weeks, or they enter a sort of hibernation for the winter, known as diapause, emerging in the spring when temperatures warm up. Populations in the northern regions have one generation per season, while populations farther south can have several generations per year. (Hossler, et al., 2008; Manley, 1993; Tuskes, et al., 1996)

How do they reproduce?

After emerging from their cocoons, adults have 1 or 2 weeks to find a mate and lay eggs. After emerging, males show pre-flight behaviors, by flexing and fluttering their wings, before taking flight. Females remain inactive their first night after emerging, and on the second night, they also show pre-flight behaviors, though they do not fly. Moths of family Saturniidae have specific "calling" times, during which females release pheromones to attract mates. To release the pheromone, females move the end of their abdomen every few seconds over a short period of time. Females rarely mate on the same night they emerge from their cocoon, but they call for mates as soon as the second night. For Io moths, calling occurs during the evening, from 9:45 to 10:30 pm. Males detect female pheromones with their antennae, once males find females, mating lasts about 90 minutes. If temperatures drop below 8 degrees Celsius, pairs may stay together until dusk the next day. If temperatures remain warm, males fly away shortly after mating. Females reportedly do not take flight until after they have mated. (Hossler, et al., 2008; Manley, 1978; Manley, 1993; Tuskes, et al., 1996)

Three to five days after mating, female Io moths lay their eggs in groups of 20 to 35 on leaves or stems of host plants, often on the undersides of leaves. Egg-laying occurs during the evening. Females can lay several hundred eggs during their short, 1 to 2 week lifespan. In the north, Io moths have only one generation per year, with adults emerging and mating from late May to mid-July. Father south, in Florida and Texas, they have two to four generations every year. In the Florida Keys, Io moths breed year round due to the warm temperatures. (Hossler, et al., 2008; Russi, et al., 1973; Tuskes, et al., 1996)

  • How often does reproduction occur?
    Io moths only breed once.
  • Breeding season
    Io moths breed from late May to July, though southern populations have multiple generations that breed earlier and later in the season.
  • Average eggs per season

Since adults only live 1 to 2 weeks, they provide no parental care for their offspring except providing nutrients in the eggs. Females also lay the eggs on plants that caterpillars can eat when they hatch. (Hossler, et al., 2008)

  • Parental Investment
  • pre-hatching/birth
    • provisioning
      • female

How long do they live?

Adults live only 1 to 2 weeks after emerging from their cocoons. (Hossler, et al., 2008)

  • Typical lifespan
    Status: wild
    7 to 14 days

How do they behave?

Caterpillars of Io moths spend much of their early instars, or developmental stages, in large groups. They are active during the day and spend much of their time feeding on leaves and plants. These caterpillars exhibit two interesting behaviors, queuing and rosette molting. In queuing, as many as 40 caterpillars gather, and travel in a line. Each caterpillar has their head against the end of the individual in front of them, and they swing their heads back and forth, as if to make sure that they are still following the line. Researchers have found the caterpillars can be placed in a continuous circle, and they will continue in this endless circle for hours, until one is blocked and changes direction, leading the line out of the circle. This behavior decreases as caterpillars grow older, though it is not uncommon to see two or three older caterpillars traveling in a line. They tend to be solitary during their last developmental stage. During rosette molting, caterpillars group together on a leaf in a rosette shape, with their heads facing outward, and their back ends together in the center of the group. They shed their skin and leave it in the center. After the molt is complete, the caterpillars turn around and eat the skins. Rosette molting decreases as caterpillars grow older, though later instars still eat molted skins. Gathering in large groups may help them look larger and more intimidating to predators. Adults do not feed, but they are active. Mating takes place at dusk, and activity continues into the night. Adults are mostly solitary. (Hossler, et al., 2008; Onuf, et al., 1977; Russi, et al., 1973; Tuskes, et al., 1996)

Home Range

There is currently no information available regarding the home range size of Io moths.

How do they communicate with each other?

When mating, Io moths communicate with pheromones. Females release pheromones to attract males, which males sense using their antennae. Adults are attracted to light and are often found at lights during the night. Adults also rely on touch, as any time they are touched, they open their wings to show the eye spots on their hindwings. Caterpillars spend much of their time in physical contact with other caterpillars, as they will line up in a queue, front to back. While queuing, each individual's head remains in contact with the end of the caterpillar in front of them, and they continuously move their heads from side to side, as if checking on the location of the caterpillar they are following. (Hossler, et al., 2008; Russi, et al., 1973; Tuskes, et al., 1996; Worth, 1979)

What do they eat?

Caterpillars of Io moths eat large amounts of leaves, and have the potential to strip branches clean. They feed on a large variety of plants; some studies have recorded at least 60 plants in their diet. Some of their preferences include willow trees and other Salix species, redbuds (Cercis), hackberries (Celtis), and species of Hibiscus, Pyrus, Ribes, Rubus, Sassafras, Prunus, and Wisteria. These caterpillars also eat their empty egg shells after hatching, as well as their molted skin. Adults do not have working mouth parts and do not feed during their short lives. (Hossler, et al., 2008; Manley, 1993; Russi, et al., 1973; Tuskes, et al., 1996)

  • Plant Foods
  • leaves

What eats them and how do they avoid being eaten?

Adult Io moths use the large eyespots on their hindwings as a defense mechanism. When resting, their front wings cover the eyespots. When disturbed, they move their front wings and display the eyespots, creating a "startle effect". The sudden appearance of "eyes" should alarm predators. Moths also have other behaviors and motions that confuse or startle predators. Caterpillars usually drop off the leaves or branches they are feeding on when they are disturbed. They also gather in large groups, which may make them appear more intimidating. Additionally, caterpillars have spines that are irritating to those that touch them. Other related Saturniidae species have venom in their spines, though the contents of Io moth caterpillar spines have not been studied. The bright colors of these caterpillars probably act as aposematic coloration, which warns predators not to eat them. Other insects prey on Io moth caterpillars, including wheel bugs (Arilus cristatus) and hornets (Vespa). (Manley, 1978; Manley, 1990; Russi, et al., 1973; Simberloff and Wilson, 1969; Tuskes, et al., 1996)

  • These animal colors help protect them
  • aposematic

What roles do they have in the ecosystem?

Caterpillars of Io moths are important herbivores, and can completely remove leaves from trees and plants with their eating habits. Some of their preferred plants include redbuds (Cercis), hackberries (Celtis), and species of Hibiscus, Prunus, Pyrus, Ribes, Rubus, Salix, Sassafras, and Wisteria. These caterpillars are also prey to several other species of insects, and can also be used as a host for several parasites. These parasites, which usually lay eggs in their larvae, include wasps of genus Cotesia, the wasp species Apanteles hemileucae, and several species of tachinid flies, Compsilura concinnata, Chetogena claripennis, and Carcelia formosa. (Onuf, et al., 1977; Schaffner and Griswold, 1934; Simberloff and Wilson, 1969; Tuskes, et al., 1996)

Commensal or parasitic species (or larger taxonomic groups) that use this species as a host

Do they cause problems?

Caterpillars of Io moths have spines that can cause irritation and pain. After the pain ends, swelling, skin redness, and hives can occur. This is fairly common for humans, especially children, who accidentally touch the caterpillars. Since these caterpillars can be found in pastures, their spines could also injure grazing livestock. Caterpillars of other Saturniidae moths may have venom in their spines that can cause severe reactions, though the spines of Io moths have not been studied. Additionally, in the early 1900s, these caterpillars were considered cotton pests in the southern United States. Since they eat leaves off plants, they have the potential to cause crop damage. (Manley, 1993; Tuskes, et al., 1996)

  • Ways that these animals might be a problem for humans
  • injures humans
    • bites or stings
  • crop pest

How do they interact with us?

There are no known positive effects of Io moths on humans.

Are they endangered?

Io moths are not an endangered species. However, as recently as 2012 their numbers in the eastern United States have decreased significantly. Due to this decline, this species could benefit from research to determine what conservation methods should be used to prevent further losses. (Manley, 1993; Wagner, 2012)


Angela Miner (author), Animal Diversity Web Staff, Leila Siciliano Martina (editor), Animal Diversity Web Staff.


Borror, D., R. White. 1970. A Field Guide to the Insects. New York: Houghton Mifflin Company.

Hossler, E., D. Elston, D. Wagner. 2008. What's eating you? Io moth (Automeris io). Cutis, 82/1: 21-24.

Manley, T. 1978. Genetics of conspicuous markings of Io moth. Journal of Heredity, 69/1: 11-18.

Manley, T. 1990. Heritable color variants in Automeris ioSaturniidae. The Journal of Research on the Lepidoptera, 29/1-2: 37-53.

Manley, T. 1993. Diapause, voltinism, and foodplants of Automeris io (Saturniidae in the southeastern United States. Journal of the Lepidopterists' Society, 47/4: 303-321.

Onuf, C., J. Teal, I. Valiela. 1977. Interactions of Nutrients, Plant Growth and Herbivory in a Mangrove Ecosystem. Ecology, 58/3: 514-526.

Peterson, A. 1962. Some Eggs of Insects That Change Color during Incubation. The Florida Entomologist, 45/2: 81-87.

Russi, K., F. Friedl, H. Russi. 1973. Queuing and rosette molting in Automeris io (Lepidoptera: Saturniidae). Entomological News, 84/2: 33-36.

Schaffner, J., C. Griswold. 1934. Macrolepidoptera and Their Parasites Reared from Field Collections in the Northeastern Part of the United States. Washington D.C.: U.S. Department of Agriculture.

Simberloff, D., E. Wilson. 1969. Experimental Zoogeography of Islands: The Colonization of Empty Islands. Ecology, 50/2: 278-296.

Tuskes, P., M. Collins, J. Tuttle. 1996. The Wild Silk Moths of North America: A Natural History of the Saturniidae of the United States and Canada. Ithaca, New York: Cornell University Press.

Wagner, D. 2012. Moth decline in the Northeastern United States. News of the Lepidopterists' Society, 54/2: 52-56.

Worth, B. 1979. Captures of large moths by an UV light trap. Journal of the Lepidopterists' Society, 33/4: 261-264.

University of Michigan Museum of ZoologyNational Science Foundation

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Miner, A. 2014. "Automeris io" (On-line), Animal Diversity Web. Accessed May 25, 2024 at

BioKIDS is sponsored in part by the Interagency Education Research Initiative. It is a partnership of the University of Michigan School of Education, University of Michigan Museum of Zoology, and the Detroit Public Schools. This material is based upon work supported by the National Science Foundation under Grant DRL-0628151.
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