Automeris io (Io moth)

Taxonomic history: Automeris io was first described by Johan Christian Fabricius in 1775. The specific epithet io references the Greek mythological figure Io, a naming convention reflecting classical allusion rather than folkloric association.

Adults have a wingspan of about 63–88 mm (2.5–3.5 inches) and exhibit sexual dimorphism: males are generally bright yellow with large plumose antennae, while females are commonly reddish-brown to purple with smaller, less plumose antennae. Both sexes bear a single large eyespot on each hindwing (black/blue rings with white center or white-filled with black and blue outer rings). Larvae hatch orange in early instars, are gregarious when young, and later instars become bright green with many urticating spines and two lateral stripes (upper bright red, lower white); mature caterpillars may reach several centimeters in length. Pupae are dark brown to black within flimsy, dark coarse-silk cocoons; some sources report a posterior ventral notch in female pupae and paired tubercles in male pupae.

Defenses / Biology: Larvae possess stinging (urticating) spines that can deliver a painful venom causing acute dermatitis (erucism); anatomical hypotheses for venom delivery include glandular cells at the base of branched setae or secretory epithelial cells. Adults are strictly nocturnal, do not feed as adults (vestigial mouthparts), live around 1–2 weeks, and employ a deimatic display by flashing hindwing eyespots (often from a head-down resting posture or when disturbed) to deter or startle predators. Females release pheromones at night to attract males, which detect them with large antennae. Eggs are laid in clusters and hatch in approximately 8–11 days; larvae pass through five instars before pupation.