Automeris io

Geographic Range

Automeris io, the Io moth, is native to the Nearctic region. It is found throughout the eastern half of the United States, as far west as Utah, Colorado, and Texas. Its range extends as far north as Quebec, Ontario, and southern Manitoba. It is also found in eastern Mexico and Costa Rica, in the northernmost portion of the Neotropical region. (Hossler, et al., 2008; Tuskes, et al., 1996)


Automeris io is a temperate species, and can be found in a variety of habitats, including deciduous woodlands, forests, meadows, agricultural orchards, suburban parks, and backyards. Larvae can be found feeding on leaves, and usually spin their cocoons to pupate in debris on the ground or in crevices among rocks or wood. (Hossler, et al., 2008; Tuskes, et al., 1996)

Physical Description

Adults of this species are considered medium to large-sized moths, with a wingspan of 5 to 9 cm. Automeris io exhibits sexual dimorphism in its coloration. Male forewings are typically bright yellow, while females have dark yellow or brown forewings. Females may also have larger, more pointed forewings. Both males and females have large eyespots on their hindwings; the eyespots are black or blue, with a gray or bluish iris surrounding a white center. The eyespot is often larger and rounder in females than in males. Adults are likely polymorphic, with a large variety of coloration across their range. Southern variations tend to have reddish-brown forewings, while other variations can be orange-brown or purple-brown. Likewise, populations in the southern region show a variation between diapausing and non-diapausing broods. Males that developed from diapausing pupae are tawny brown, while non-diapausing males are yellowish with some red. Early instars of larvae are brown, yellow, or dull orange, and are 3 to 4 mm in length when newly hatched. Later instars are bright green, with 2 distinctive lateral stripes, a red one on top and a white stripe just below. 4th and 5th instars grow to 3 to 5 cm in length. All instars have bifurcated urticating spines. Eggs are oblong with a flattened top. They are white when 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 tinted with 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


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 fill and expand. After finding mates, females lay eggs on host plants. After about 10 days, the eggs hatch. All eggs hatch within 1 to 3 days of each other; the larvae do not leave until all have emerged. Larvae (commonly known as caterpillars) go through five instars, which takes about 4 weeks. The larvae eat continuously, before becoming pupae and spinning cocoons. The cocoon takes 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 as adult moths within a few weeks, or they enter diapause for the winter, emerging in the spring when temperatures warm up. Populations in northern regions are univoltine, with one generation per season, while populations farther south can have several generations per year, and some broods that do not diapause over winter. Diapausing pupae will not develop unless they experience the cold period, while non-diapausing pupae are very susceptible to cold temperatures. (Hossler, et al., 2008; Manley, 1993; Tuskes, et al., 1996)


After eclosion from their cocoons, adults have 1 or 2 weeks to find a mate and deposit eggs. After eclosion, males exhibit pre-flight posturing, by flexing and fluttering their wings, before taking flight. Females remain inactive the first night, and on the second night, they also show pre-flight posturing, though they do not take flight. Moths of family Saturniidae have specific "calling" times, during which females release pheromones to attract mates. To release pheromones, females extend and retract their last abdominal segment every few seconds over a short period of time. Females rarely mate on the night of their emergence, but they will call for mates as soon as the second night after eclosion. For Automeris io, calling occurs during the evening, from 9:45 to 10:30 pm. Males detect female pheromones with their antennae, once a male locates a female, copulation lasts for about 90 minutes. If temperatures drop below 8 degrees Celsius, pairs may remain together until dusk the next day before separating. If temperatures remain warm, males fly away shortly after copulation. 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, females lay their eggs in clusters of 20 to 35 on leaves or stems of suitable host plants, often on the undersides of foliage. Oviposition occurs during the evening. Females can lay several hundred eggs in their short, 1 to 2 week lifespan. In the north, Automeris io has only one generation per year, with adults emerging and mating from late May to mid-July. Father south in Florida and Texas, it has two to four generations every year, producing several broods of non-diapausing adults before producing pupae that diapause over winter. Populations in the Florida Keys breed year round due to the warm temperatures. (Hossler, et al., 2008; Russi, et al., 1973; Tuskes, et al., 1996)

  • Breeding interval
    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 care for their offspring, although they do deposit the eggs on a suitable host plant and provide provisioning in the eggs. (Hossler, et al., 2008)

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


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

  • Typical lifespan
    Status: wild
    7 to 14 days


Caterpillars of Automeris io spend much of their early instar stages in large groups. They are active during the day and spend much of their time feeding on the leaves and plants they live on. These larvae exhibit two interesting behaviors, queuing and rosette molting. In queuing, as many as 40 caterpillars gather, and travel in a procession. Each caterpillar has their head against the posterior of the individual in front of them; they continually swing their heads from side to side, as if to confirm their position. Researchers have found the caterpillars can be placed in a continuous circle, and will continue in this endless circle for hours, until one is deliberately blocked and diverts the queue in another direction. This behavior decreases as larvae grow older, though it is not uncommon to see two or three later instar larvae traveling in a line. The last instar tends to be solitary. During rosette molting, caterpillars group together on a leaf in a rosette shape, with their heads facing outward, and their posterior ends together in the center of the formation. They molt, and the molted skins (exuviae) are left in the center of the rosette. After the molt is complete, the larvae turn themselves around and eat the exuviae. Rosette molting decreases as larvae grow older, though later instars still eat the exuviae. Gathering in large groups may serve as a defense mechanism, allowing the caterpillars to 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 largely 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.

Communication and Perception

When mating, adults of Automeris io communicate with pheromones. Females release pheromones to attract males, which males detect with their plumose antennae. Adults are attracted to light and are often be found at lights during the night. Adults also rely on tactile cues to initiate their defense mechanisms, as any time they are touched, they open their wings to reveal their hindwing eye spots. Larvae spend much of their time in physical contact with other larvae, as they line up in a procession or queue, front to back. While queuing, each individual's head remains in constant contact with the posterior of the caterpillar in front of them, and they continuously move their heads from side to side, as if confirming the position and presence of the caterpillar they are following. (Hossler, et al., 2008; Russi, et al., 1973; Tuskes, et al., 1996; Worth, 1979)

Food Habits

Larvae of Automeris io eat large amounts of leaves, with the potential to defoliate plants and strip branches clean. They feed on a large variety of plants. Some studies have recorded at least 60 plants in their diet, including most major groups of angiosperms. Some 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 (exuviae). Adults have vestigial mouth parts, but do not feed during their short lifespan. (Hossler, et al., 2008; Manley, 1993; Russi, et al., 1973; Tuskes, et al., 1996)

  • Plant Foods
  • leaves


Adults of Automeris io use the large eyespots on its hindwings as a defense mechanism. At rest, its forewings cover its eyespots. When disturbed, it "flexes" its wings and displays the eyespots, creating a 'startle effect'. This is often accompanied by behaviors that confuse or startle predators. Larvae tend to drop off the leaves or branches they are feeding on when disturbed. They also gather in large groups, which may make them appear more intimidating to predators. Additionally, all larval instar stages have urticating spines that are irritating to those that come into contact with them. Other related Saturniidae species have venom or histamines in their spines, though the contents of Automeris io larval spines have not been studied. The bright larval colors likely serve as aposematic coloration, warning predators to avoid them. Other insects prey on the larvae, including wheel bugs (Arilus cristatus) and hornets (Vespa). (Manley, 1978; Manley, 1990; Russi, et al., 1973; Simberloff and Wilson, 1969; Tuskes, et al., 1996)

Ecosystem Roles

Larvae of Automeris io are important herbivores, and can completely strip branches of trees and plants. Some of the preferred host 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 host several parasites. These parasites, which typically 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/Parasitic Species

Economic Importance for Humans: Positive

There are no known positive effects of Automeris io on humans.

Economic Importance for Humans: Negative

Caterpillars of Automeris io have urticating spines that can cause irritation and pain. After the pain subsides, swelling, erythema, and urticaria can occur. This is a relatively common occurrence for humans, who may accidentally touch the caterpillars, and can especially be a problem for children. The spines could also potentially injure the mouths of grazing livestock, as these caterpillars can be found in pastures. Larvae of other Saturniidae moths may contain venom or histamines in their spines that can cause severe reactions, though the contents of Automeris io spines have not been analyzed. Additionally, in the early 1900s, these caterpillars were considered a pest of cotton in the southern United States, and can potentially cause crop damage. (Manley, 1993; Tuskes, et al., 1996)

  • Negative Impacts
  • injures humans
    • bites or stings
  • crop pest

Conservation Status

Automeris io has no special conservation status, although in 1993 their numbers declined significantly in the eastern United States. Another report in 2012 also found a decreasing population trend in the same region, as they became more localized. Due to this decline, this species could benefit from research assessing populations to determining what conservation methods can be taken to prevent any further loss. (Manley, 1993; Wagner, 2012)


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



living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map


living in the southern part of the New World. In other words, Central and South America.

World Map


living in landscapes dominated by human agriculture.


having coloration that serves a protective function for the animal, usually used to refer to animals with colors that warn predators of their toxicity. For example: animals with bright red or yellow coloration are often toxic or distasteful.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


uses smells or other chemicals to communicate


a period of time when growth or development is suspended in insects and other invertebrates, it can usually only be ended the appropriate environmental stimulus.

  1. active during the day, 2. lasting for one day.

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature


union of egg and spermatozoan


an animal that mainly eats leaves.


forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.


An animal that eats mainly plants or parts of plants.


having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

internal fertilization

fertilization takes place within the female's body


A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.


having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.


active during the night


reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.


chemicals released into air or water that are detected by and responded to by other animals of the same species


"many forms." A species is polymorphic if its individuals can be divided into two or more easily recognized groups, based on structure, color, or other similar characteristics. The term only applies when the distinct groups can be found in the same area; graded or clinal variation throughout the range of a species (e.g. a north-to-south decrease in size) is not polymorphism. Polymorphic characteristics may be inherited because the differences have a genetic basis, or they may be the result of environmental influences. We do not consider sexual differences (i.e. sexual dimorphism), seasonal changes (e.g. change in fur color), or age-related changes to be polymorphic. Polymorphism in a local population can be an adaptation to prevent density-dependent predation, where predators preferentially prey on the most common morph.

seasonal breeding

breeding is confined to a particular season


offspring are all produced in a single group (litter, clutch, etc.), after which the parent usually dies. Semelparous organisms often only live through a single season/year (or other periodic change in conditions) but may live for many seasons. In both cases reproduction occurs as a single investment of energy in offspring, with no future chance for investment in reproduction.


reproduction that includes combining the genetic contribution of two individuals, a male and a female


associates with others of its species; forms social groups.


lives alone


living in residential areas on the outskirts of large cities or towns.


uses touch to communicate


that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).


Living on the ground.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.


A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.


uses sight to communicate


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.