What's in a band? The function of the color and banding pattern of the Banded Swallowtail

Abstract

Butterflies have evolved a diversity of color patterns, but the ecological functions for most of these patterns are still poorly understood. The Banded Swallowtail butterfly, Papilio demolion demolion, is a mostly black butterfly with a greenish‐blue band that traverses the wings. The function of this wing pattern remains unknown. Here, we examined the morphology of black and green‐blue colored scales, and how the color and banding pattern affects predation risk in the wild. The protective benefits of the transversal band and of its green‐blue color were tested via the use of paper model replicas of the Banded Swallowtail with variations in band shape and band color in a full factorial design. A variant model where the continuous transversal green‐blue band was shifted and made discontinuous tested the protective benefit of the transversal band, while grayscale variants of the wildtype and distorted band models assessed the protective benefit of the green‐blue color. Paper models of the variants and the wildtype were placed simultaneously in the field with live baits. Wildtype models were the least preyed upon compared with all other variants, while gray models with distorted bands suffered the greatest predation. The color and the continuous band of the Banded Swallowtail hence confer antipredator qualities. We propose that the shape of the band hinders detection of the butterfly's true shape through coincident disruptive coloration; while the green color of the band prevents detection of the butterfly from its background via differential blending. Differential blending is aided by the green‐blue color being due to pigments rather than via structural coloration. Both green and black scales have identical structures, and the scales follow the Bauplan of pigmented scales documented in other Papilio butterflies.

In vivo visualization of butterfly scale cell morphogenesis in Vanessa cardui

“…By tailoring these scale morphologies, butterflies produce unique visual appearances ( 4 – 7 ), ensure thermal regulation ( 8 ) and water repellency ( 9 ), or generate beneficial acoustic ( 10 ) and aerodynamic effects ( 11 ). Interdisciplinary interest in these material functionalities has led to scientific advances in the comprehensive assessment of the scales’ multifunctional material properties ( 12 ), design of next-generation bioinspired functional materials ( 13 , 14 ), identification of key genes in patterning and structural color ( 15 – 19 ), and evaluation of the impact of ecological factors on biodiversity ( 20 , 21 ). Although the enviable functionality of butterfly wings depends heavily on the precise structural architecture of the wing scales, little is known about the dynamics, processes, and phenomena involved in scale development ( 22 ).…”

Butterfly Wing Translucence Enables Enhanced Visual Signaling

“…The biological function of the distinct midband in the wings encountered in many papilionoid species has been investigated with behavioral assays on Papilio demolion Linnaeus, 1758 [ 35 ]. The greenish-blue color of the band, created by pigmented scales, was found to support differential blending into the background, whereas the shape of the band hinders the detection of the butterfly through coincident disruptive coloration.…”

Age and Appearance Shape Behavioral Responses of Phasmids in a Dynamic Environment

“…Future studies to test the predictions about the role of particular behaviors as antipredator strategies will need to determine how likely predators are to detect phasmids. Using prey models that systematically vary in size, coloration, posture, and location (e.g., Cuthill and Székely, 2009;Webster et al, 2009;Tan et al, 2016Tan et al, , 2020, it will be possible to elucidate the importance of these characteristics for concealment and predator avoidance in phasmids. Field observations can provide information about the range of natural predators of phasmids and indicate the preferred foraging microhabitats of the predators.…”