Butterfly eyespots are striking circular or oval markings found on the wings of many species. These patterns often resemble the eyes of vertebrates, creating a visually compelling feature. Eyespots are a widely studied phenomenon, recognized for their distinct appearance and widespread presence in butterfly coloration and pattern diversity.
Appearance and Structure
Butterfly eyespots display a series of concentric rings, often featuring contrasting colors like black, white, yellow, and sometimes blue. A central dot or core, sometimes called a “pupil,” completes the eye-like illusion. These intricate patterns are formed by specialized scales on the wings, which contain specific pigments or structural elements that create the colors. The arrangement and pigmentation of these scales contribute to the precise circular design. Eyespots vary considerably in size, from small, subtle dots to large, prominent markings that dominate a significant portion of the wing.
Functions of Eyespots
Eyespots serve multiple functions, primarily related to defense against predators. One role is predator deterrence, which can startle or intimidate an attacker. Large, sudden displays of prominent eyespots, such as those on the peacock butterfly, can momentarily frighten predators like birds or lizards, allowing the butterfly to escape. This “fake eye” hypothesis suggests these markings mimic the eyes of a larger, threatening animal, causing the predator to hesitate or retreat.
Eyespots also deflect predator attacks away from the butterfly’s vital body parts. Smaller eyespots, often on the outer margins of the wings, can draw a predator’s strike to a less vulnerable area. If a wing margin with an eyespot is attacked, the butterfly can survive with only wing damage, increasing its chances of survival.
Beyond defense, eyespots play a role in sexual selection and mate recognition in some species. In certain butterflies, like Bicyclus anynana, eyespot patterns on the dorsal wing surface, often concealed from predators, may influence mate choice. Females may select males based on characteristics like eyespot size or brightness.
How Eyespots Develop
The formation of butterfly eyespots primarily occurs during the pupal stage of metamorphosis. During this period, specific regions on the developing wing, known as “organizing centers” or “foci,” direct the formation of the concentric rings. These foci act as signaling centers, releasing chemical signals or morphogens that create a gradient across the wing tissue.
The concentration of these signals determines the fate of the surrounding scale cells, dictating which pigments they will produce and how they will arrange to form the distinct color rings. Genetic pathways involving genes like Distal-less (Dll), spalt (sal), and Antennapedia (Antp) are involved in this patterning. The precise timing and location of these signals shape the final eyespot pattern, demonstrating an interplay between genetic programming and developmental cues.
Eyespot Diversity Across Species
Butterfly and moth species exhibit a wide array of eyespot forms. The number of eyespots can range from a single pair to multiple rows across both forewings and hindwings. Their size also varies considerably, from tiny, inconspicuous dots to very large, prominent markings, sometimes resembling an owl’s eyes, as seen in the owl butterfly (Caligo genus).
Eyespots can be located on different parts of the wings, appearing on forewings, hindwings, or both. Their coloration and complexity also differ, ranging from simple rings to intricate patterns that may include iridescent scales, creating a shimmering effect. For instance, the peacock butterfly (Inachis io) is known for its large, striking eyespots, and the owl butterfly for its particularly convincing, large eye-like markings.