Underwing Moth

A two-stage defense

Underwing moths display one of the most refined two-stage defense strategies in insects:

Stage 1 — Camouflage at rest. The forewings are gray, brown, or mottled to match tree bark almost perfectly. A resting underwing moth disappears against an oak trunk. Most predators never spot them.

Stage 2 — Flash startle. If a predator does detect the moth, it suddenly flashes brightly colored hindwings — typically red, orange, pink, yellow, white, or black-and-white — that were hidden when the wings were folded. The flash startles the predator long enough for the moth to escape into nearby foliage. Once it lands and folds its wings, the bright colors vanish, leaving the predator looking for a different prey item.

The strategy is so effective that many underwing species have flourished despite specialized predators (especially nocturnal birds and bats).

Diversity hotspot

The genus Catocala contains over 200 species worldwide, with the highest diversity in North America (about 110 species) — particularly in eastern deciduous forests. Each species has a distinctive hindwing color pattern that’s used in identification:

• Catocala ilia — red hindwings.
• Catocala relicta — black-and-white “white underwing.”
• Catocala amica — yellow-orange.
• Catocala epione — black with a white border.

The genus name Catocala combines Greek kata (“below”) + kalos (“beautiful”) — beautiful underneath, plain above. The folded wings resemble bark; spread, they’re stunning.

Caterpillar host specificity

Each underwing species typically depends on one or a few host plants:

• Oak underwings — feed only on oak leaves.
• Walnut underwings — feed on walnut, hickory, or pecan.
• Willow underwings — feed on willow species.
• Locust underwings — feed on black locust.

The host-plant specificity makes underwing populations vulnerable to forest changes. Many underwings have declined as their host trees have been lost or changed by introduced pests (oak wilt, emerald ash borer, etc.).

”Sugaring” for moth viewing

A traditional moth-watching technique used by 19th and 20th century naturalists: paint a mixture of fermented fruit, beer, and brown sugar on tree trunks at dusk. The fermenting bait attracts large numbers of underwing moths and other large nocturnal moths. Modern entomologists still use the technique to survey moth populations.