Io Moth

The Io Moth is a medium-sized member of the giant silkmoth family Saturniidae, found across much of eastern and central North America. It is one of the most recognizable saturniid moths thanks to the enormous, false eye-like markings on its hindwings, which are concealed at rest and revealed suddenly when the moth is disturbed.

The species shows pronounced sexual dimorphism: males are bright yellow with a slimmer body, while females are larger and colored in shades of reddish-brown to purplish-brown, a difference striking enough that the two sexes are sometimes mistaken for different species by beginners.

Io Moth caterpillars are pale green with rows of branching, spine-covered tubercles and are gregarious when young, often seen feeding in groups along a branch before dispersing as they mature.

• Hindwings bear a single large, dark eyespot with a blue-black center and white highlight, ringed in yellow or pink, concealed beneath the forewings at rest.
• Males are bright yellow overall; females are larger and colored reddish-brown to purplish-brown, both with the same eyespot pattern.
• Forewings are relatively plain, mottled in the wing's base color with a fine dark line near the outer margin.
• When disturbed, the moth flicks its forewings forward to suddenly expose both hindwing eyespots, a startle display meant to deter predators.
• The caterpillar is pale green with a reddish-and-white side stripe and covered in clusters of branching spines.

Found across much of the eastern and central United States and into southern Canada, the Io Moth inhabits deciduous woodlands, forest edges, hedgerows, and suburban yards with a variety of host trees and shrubs. Adults are nocturnal and most often encountered at porch lights or other artificial light sources during the warmer months.

The species can produce one or two generations per year depending on latitude, with adults flying from late spring through summer.

Adult Io Moths do not feed, as is typical for giant silkmoths, and focus their brief lives entirely on mating. Their signature defense is the sudden hindwing eyespot display, flashed when a resting moth is disturbed, intended to startle or confuse potential predators by mimicking the eyes of a larger animal.

Caterpillars feed gregariously in early instars, moving and resting together in tight clusters along host plant stems, before becoming more solitary as they near maturity. The caterpillar is covered in branching spines that can sting in defense, a defensive trait among Automeris species.

Eggs are laid in clusters on the leaves of a wide range of host plants, including willow, maple, and roses, among many others. Caterpillars hatch and feed together in groups through early instars before dispersing, molting several times and developing their characteristic spine-covered tubercles.

Mature caterpillars spin a thin, papery cocoon, often among leaf litter at the base of the host plant, and pupate there through winter in northern populations. The species can be univoltine or bivoltine depending on climate, with adults emerging to mate and lay the next generation's eggs.