What are eyespots on a butterfly wing?

Eyespots are roughly circular markings, usually made of concentric rings of contrasting colour, that resemble a vertebrate eye. They appear on the wings of many butterfly and moth families and serve one of two main defensive functions: startling or intimidating a predator, or deflecting an attack toward an expendable part of the wing.

How do eyespots protect a butterfly from predators?

Small eyespots near the wing margin tend to redirect a predator's strike toward the wing edge rather than the body, so the butterfly loses only a piece of wing and survives; large, prominent eyespots — especially when suddenly revealed, as in some Morpho and owl butterflies — instead work by startling or briefly frightening a predator such as a bird, buying the butterfly a moment to escape.

Are eyespots the same in every butterfly species?

No. Eyespot size, number, and placement vary enormously between species and even between the wing's upper and lower surfaces of the same individual, and their function is tuned accordingly — the huge, hidden upperside eyespots of some Morpho species stay concealed at rest and are flashed suddenly only when disturbed, while small marginal eyespots on species like fritillaries and heaths are visible at all times and work through the deflection mechanism instead.

Butterfly Atlas

Eyespots

~1 min

Eyespots are circular wing markings that mimic a vertebrate eye, used by butterflies either to startle predators or to redirect attacks away from vital body parts.

Definition

Eyespots are roughly circular wing markings, usually composed of concentric rings of contrasting colour, that visually resemble a vertebrate eye. They occur widely across butterflies and moths and are one of the best-studied examples of how a simple visual pattern can serve a specific, testable anti-predator function rather than existing merely for display.

Despite their superficial similarity across species, eyespots are not a single strategy — biologists distinguish at least two distinct defensive mechanisms depending on the eyespot's size, position, and visibility.

Deflection: small eyespots at the wing margin

Small eyespots positioned near the outer edge of the wing work through deflection: a predator, especially a bird, tends to aim its strike at the most conspicuous part of a fleeing target, and a bright marginal eyespot draws that strike toward an expendable piece of wing rather than the butterfly's body. A butterfly that loses a wing-edge fragment to a deflected strike survives and can often still fly reasonably well, while a strike aimed at the body would be fatal. Many fritillaries and heaths, including species like the Cardinal (Argynnis pandora), carry exactly this kind of small, marginal eyespot pattern.

Intimidation: large, suddenly-revealed eyespots

Large eyespots, often concealed on a wing surface that stays hidden while the butterfly rests, work through a different mechanism: startle or intimidation. When disturbed, the butterfly abruptly reveals the hidden eyespots — by flicking open folded wings — presenting a predator, especially a small bird, with a sudden pattern resembling the eyes of a larger animal. The brief hesitation this triggers is often enough for the butterfly to escape. Some Peleides Blue Morpho (Morpho peleides) relatives and owl butterflies use exaggerated versions of this strategy, with eyespots large enough to dominate the entire wing surface.

Why eyespot function is testable

Eyespot function is one of the rare cases in evolutionary biology where the adaptive hypothesis has been directly tested experimentally: researchers have manipulated eyespot size, number, and visibility on live and model butterflies and measured how wild predators respond, consistently finding that larger, more eye-like spots deter attack more effectively than smaller or asymmetric ones, and that marginal spots specifically increase the rate of survivable wing-edge damage relative to fatal body strikes.