Imperial moth vs Io moth
These two are easy to mix up. Here's how to tell an imperial moth from an Io moth, and whether either one bites or stings.
Imperial moth
Eacles imperialis
Io moth
Automeris io
≠The key differences
Io moths are smaller, and adults show a single large eyespot on each hindwing; their caterpillars are green with stinging spines, unlike the harmless imperial caterpillar.
⚖︎Side by side
| Imperial moth | Io moth | |
|---|---|---|
| To humans | Non-toxic | Stinging caterpillar |
| Size | Wingspan 80-175 mm (3-7 inches), typically 90-150 mm in many populations | 50-80 mm wingspan |
| Colours | Yellow, Orange, Rusty brown, Purple-brown markings | Yellow, Reddish brown, Green (caterpillar), Blue (eyespots), Black (eyespot center) |
| Family | Saturniidae | Saturniidae |
| Habitat | Deciduous and mixed woodlands, forest edges, suburban yards with host trees | Woodlands, forest edges, fields, gardens and riparian areas where host plants grow |
| Range | Eastern and central North America from Canada (southern Ontario, Quebec) south through the eastern United States to Mexico; exact range and form vary regionally | Eastern and central North America — from southern Canada through the United States and into parts of Mexico |
| Active | Mostly spring to early autumn depending on location; adults are nocturnal and fly at night | Spring to late summer depending on latitude; adults are nocturnal |
| Pest? | No | Yes |
🔍How to spot an imperial moth
- Large wingspan (typically 90-150 mm) with rounded fore- and hindwings.
- Ground colour yellow to orange with distinct purple-brown blotches and wavy crosslines.
- Small dark discal spot on each wing and males with feathery antennae.
- Caterpillars large, green or brown/orange, with long whitish hairs and short horns behind the head.
🔍How to spot an Io moth
- Hindwings with a single large eyespot on each side: black-and-blue center with a white mark, on a yellow background
- Sexual dimorphism: males bright yellow, females reddish-brown on forewings
- Caterpillars bright green with branched stinging spines and a red-and-white stripe along each side
?Frequently asked questions
What is the difference between an imperial moth and an Io moth?
Io moths are smaller, and adults show a single large eyespot on each hindwing; their caterpillars are green with stinging spines, unlike the harmless imperial caterpillar.
Is an imperial moth or an Io moth more dangerous?
Imperial moth: Non-toxic. Io moth: Stinging caterpillar. Imperial moths and their caterpillars are not venomous. Io moth caterpillars have urticating spines that inject irritant when they break the skin.
Identification from photos is never certain: don't handle insects you can't identify, and get medical advice for bites, stings or allergic reactions.