8 July 2022

When Mike Fialkovich sent me photos of a regal moth laying eggs on a metal fence near his office I wondered if this female was making a mistake. The fence has no food for her tiny caterpillars. What will her larvae eat when they hatch?

The regal or royal walnut moth (Citheronia regalis) is the largest moth north of Mexico with a wingspan of 3.94 to 6.25 inches (females are largest). The adult moth never eats — its only job is to reproduce — but its caterpillars feast on trees including hickories, pecans, black walnuts, sweet gum, persimmon and sumacs.

Normally their lives unfold like this.

Adults emerge in late evening and mate the following evening. Females begin laying eggs at dusk the next day, depositing them in groups of 1-3 on both sides of host plant leaves. Eggs hatch within 6-10 days, and the caterpillars (known as the Hickory Horned Devil) feed alone. Young caterpillars rest on the tops of leaves and resemble bird droppings, while older caterpillars appear menacing because they are very large and brightly colored with red “horns” near the head. Caterpillars pupate in a burrow in the soil.

— Royal walnut moth account at butterfliesandmoths.org

There’s no explanation for why this moth chose a fence. Did it “smell” like a hickory?

Her caterpillars, called hickory horned devils, will need a lot of food to reach this size before they pupate.

It looks like a mistake to me but we’ll have to wait and see.

(photos of regal moth by Mike Fialkovich, hickory horned devil photo from Wikimedia Commons)