Butterfly Wing Structure – Transparency Edition

In the past I have posted about some of my experiences with the Foldscope in the Amazon rainforest, and more recently about investigating structural color in butterflies in the field (see here and here). I even just realized that others have made posts contributing to a butterfly scale database!

For this particular trip to Ecuador, I was interested in species of butterflies and moths that display transparency in their wings.

GlasswingHaetera

At first you might say to yourself, well maybe these butterflies just lack scales within the transparent regions. However, taking a look with the Foldscope tells a different story…

Haetera_Compilation_Yellow

Notice in this Haetera butterfly species that the transparent wing is in fact covered in scales. Looking at a different region (the colorful eyespot on the wing) reveals completely different scale morphology.

Citherias_1_Compilation

Here is a Cithaerias butterfly, commonly known as the Blushing Phantom. The scale structures in the transparent region appear different than the Haetera.

Glasswing_Comp2

The above are particularly interesting, butterflies commonly known as Glasswings. The scales in the transparent regions appear a bit forked and the colorful scales (likely containing pigments) have a completely different morphology.

By looking at just a handful of transparent butterflies, already we can begin to hypothesize that nanostructure development that produces wing transparency could have evolved multiple times and perhaps butterflies can achieve transparency in completely different ways.

What are your thoughts? The physics behind nanostructures that allow for transparency is truly intriguing and I hope to delve into this further.

 

 

 

6 Comments Add yours

  1. Manu Prakash says:

    Fascinating post @Aaron – as usual 🙂

    Thrilled to see the images; completely different from what unwound have expected from a “glass” butterfly. I am infinitely intrigued by the question you posed. More so; I realize making something completely transparent is hard – since random light scattering in the scale structure could have given rise to a translucent wing – but to be completely transparent; you need to not scatter too much light.

    Secondly, it appears the spacing of the scales is not modified (density seems similar to past scale images you have shared); which leads me to believe that transparency does not arise from sparseness.

    Would be very interesting if you images a transparent section in cross section. I have shared some tricks in the past for imaging leaf sections – which would apply well here.

    I hope you will have some small samples with you when you return; and I will eagerly wait to see these in real life. It’s almost unbelievable..

    Cheers
    Manu

    1. Saad Bhamla says:

      Awesome post Aaron.
      I noticed that you don’t have glares on the wings in the transparent region, which does mean that the wings has some structure to scatter light on the nanoscale.

      Interesting question. I wonder if it’s transparent from all angles – what I’m getting at is when it flies, the angle of sunlight hitting it changes – so does it appear transparent at all angles?

      The second thing is that butterflies have really good vision in UV- so now I’m wondering if the spots are transparent to UV light. You can easily check this by using a simple experiment.

      Very cool. Thanks for sharing 🙂

      Saas

  2. Manu Prakash says:

    Glares as a simple diagnostic tool is a fantastic suggestion @saad. For the butterfly; it’s useful to get the broadest transparency – since glare is a bad camouflage.

    A side question to @aaron (also @saad); while we are in the issue of butterfly wings; do you know of a butterfly with “mirrors” as wings. Ask @Nipam? I am curious..

    Cheers
    Manu

    1. Aaron Pomerantz says:

      I will have to check with Nipam, but I am at least aware of some amazing species where the chrysalis is like a mirror http://www.alexanderwild.com/Insects/Insect-Orders/Lovely-Lepidoptera/i-8g6BzBb

  3. Aaron Pomerantz says:

    @Manu and @Saad, thanks very much for the insightful comments. A wing cross section will definitely be on my to-do list.

    We know very little about transparency beyond some recent fascinating studies in Greta oto. In this case, omnidirectional anti-reflection is caused by small nanopillars covering the transparent regions of its wings – the pillars are irregularly arranged and feature a random height and width distribution (http://www.nature.com/ncomms/2015/150422/ncomms7909/abs/ncomms7909.html)

    @Saad you bring up a very good point with UV reflectance. Even more incredible, transparent members of the family Nymphalidae exhibit polarized wing reflectance. Thus, transparency could serve as an anti-predatory strategy while also having adaptive communicative value (http://jeb.biologists.org/content/210/5/788).

    However, in this post I have shown members belonging to several different genera, and transparency is found across a wide-range of butterfly families, as well as moth families. The function, physical properties, and genetic development of transparent microstructures across these members are largely unknown!

  4. laksiyer says:

    @Aaron I am blown away as usual. 1) Could you make your pictures clickable so that we could inspect them individually (I think you could do this while editing the picture and click link to media. Once you choose to link a picture to media it does so every time). Do you think transparency in butterfly wings evolved many times independently? Further, do these scales drop off or are they rigid? Do you know the most common predators of these? Are these active only during the day? I wonder how these would deal with sound waves? Love reading about your adventures.

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