Glasswing Butterfly
2025-06-22
Once, I asked the question in conservation ecology to a guest lecturer about why glass wing butterflies might have evolved to have clear wings. I believe it was the Chief of the Wilder Institute at the Calgary Zoo.
The lecturer pointed out that other insects had transparent wings and was it really that unusual in that light? In that moment, I was impressed but I've thought about it enough and dislike the answer.
Of course it is still unusual to me! Does that mean glass wing butterflies aren't technically butterflies or are more ancestral to other scaled butterflies? The more interesting idea is whether an ancestor had scales at one point and evolved to have clear wings again.
Glasswing butterflies are actually a large clade. Greta oto is probably the most well known but they are grouped into a tribe named Ithomiini that all have clear wings in varying degrees.
Evolutionarily, it looks like the butterflies have independently developed different methods to have clear wings compared to actual clear winged species like dragonflies. Lepidoptera's nearest neighbours are Caddisflies, who have opaque wings. When I port the phylogenies into Timetree and check the Greta oto's neighbours, they have various patterns of transparency. It is a range for this family!!
One paper studied Greta oto wing development and found that in transparent regions, they developed bristles to alternate with scales and decreased the density of growth. The bristles were covered in wax which was found to disperse/absorb light to prevent glare. Opaque regions were completely scaled and were relatively longer than the scales found in the transparent region. This is unique to butterflies, as other insects have smooth wings and lack scales.