A team of mathematicians and scientists needed x-ray tomography to confirm that wings of the fruit-sucking moth are, in fact, flat despite appearing 3D. The novel visual illusion is produced by specialised nanostructures found in select parts of the wing.
Masquerading as an inedible object is a type of camouflage with stunning examples including butterflies that look like bird droppings and moths that look like snake heads.
The fruit-sucking moth – which is native to southeast Asia and northern Queensland, Australia – has evolved to masquerade as a crumpled leaf. The surface of the moth’s forewings, which are visible when it is at rest, are complete with veins, mould spots and regions of shininess that mimic 3D curvature.
X-ray tomography, which is not susceptible to visual illusions in the visible spectrum, confirmed that the underlying structure of the moth’s wings is uniform and featureless.
“What is remarkable about this moth, however, is that it is creating the appearance of a three-dimensional object despite being almost completely flat,” says lead author Jennifer Kelley of the University of Western Australia. “This is the novel find to our study.”
Insects are well known to use structural coloration, where tiny variations in the wing’s scales produce visual effects. So, Kelley and colleagues used scanning electron microscopy (SEM) imaging to compare the microscopic wing scale structure across the wing.
Most of the wing is made of scales that had the typical nanostructure seen in most moths: two layers with the top layer made of regular “window-like” rectangular holes. The windows allow most of the light hitting the scale to reflect off the lower layer. This nanostructure scatters light in a diffuse pattern and does not appear shiny.
In shiny regions of the wing, however, the team found specialised scale nanostructures. Here, the top layer had rectangular windows but these windows varied in size across the scale. This variation, combined with unevenness in the height of the scale’s top layer, scatters light in a directional pattern to produce a shiny effect.
“It is intriguing that the nanostructures which produce shininess only occur on the parts of the wing that would be curved if the wing was a leaf,” says Kelley. “This suggests that moths are exploiting the way predators perceive 3D shapes to improve their camouflage, which is very impressive.”
The fruit-sucking moth’s masquerade is likely to confuse predators, such as birds, that are active during the day.
While Kelley and colleagues suggest their findings could be applied to advanced human camouflage technologies, the research adds to the group’s growing corpus on moth coloration adaptations. Their previous collaboration explored shape-shifting wing patterns in a related moth species.
The latest research is published in the journal, Current Biology.
