It's not a butterfly — it's a moth! Learn how to identify the promethea silk moth, a beautifully patterned backyard visitor.
How to Identify a Promethea Silk Moth
Published on Mar. 14, 2025
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What Does a Promethea Moth Look Like?
Finding a promethea moth can be tricky, but they’re not difficult to identify once you’ve located one. Males have mostly black wings with beige borders; females appear more colorful with reddish-brown bodies and a gradient pattern on the wings, leading to a beige border at the edges. Their wingspan ranges from approximately 3 to 4 inches.
Promethea silk moths flit through the eastern half of the United States. Recently, their numbers have been declining as a result of predation from the tachinid fly.
Discover more silk moths that might be in your backyard.
Ask the Experts: Moth or Butterfly?
A Birds & Blooms reader recently spotted one of these moths and wrote to our experts for help identifying it. “This butterfly (above) stopped by last Memorial Day. It came early morning and left in the evening. What is it?” asks Lois Bianco of Utica, New York.
Kenn and Kimberly Kaufman say, “That’s a lucky sighting. It’s as big as a large butterfly but it’s actually a moth, a female promethea.
These beautiful creatures are only around for a few days after they emerge from their cocoons in late spring or early summer. The adults don’t feed on anything—they can’t because they lack working mouth parts—so they live just long enough to find mates and for females like this one to lay eggs.
Their caterpillars feed on leaves from a variety of trees and shrubs during the summer, then spin their cocoons at the approach of winter.”
Learn how to identify a luna moth.
Caterpillar and Host Plants
Caterpillars go through several instars before creating a cocoon. These instars range from white-and-black striping to green with blue spots on the back. Caterpillars feed in a group at first, while older caterpillars feed on their own. Spicebush, sassafras, sweet bay, white ash, and lilac all serve as host plants.
Promethea Moth Life Cycle
As moths and butterflies do, the promethea silk moth starts its life as a caterpillar. After feeding on the leaves of its host plants and breaking away from the group of feeding caterpillars, it forms a cocoon around a leaf. In the northern portion of its range, the caterpillar remains in a cocoon through winter and emerges as a moth in the spring.
Adult promethea silk moths lack the ability to eat, so they live long enough only to reproduce and, in the case of females, lay eggs.
Sources
- Vermont Center for Ecostudies, “Promethea Silkmoth“
- Bug of the Week, “Promethea Silk Moth“
- iNaturalist, “Promethea Silkmoth“
About the Experts
Kenn and Kimberly Kaufman are the official bird experts for Birds & Blooms. They are the creators of the Kaufman Field Guide series and they lead birding trips all over the world.
