by Andre on 30 July 2006
It is well known, and well documented, that butterflies and moths have beautifully microstructured wings that give rise to their iridescent colours. It’s easy to find pictures of these structures and studies of their colour production and other optical properties. What I’ve been having a harder time learning about though is the nanostructures found on some other insect wings.
This story starts, as others have before it, with a walk around campus during an otherwise regular work day. The ground treasure that caught my eye this time was a dead, but externally undamaged, insect with widely separated eyes, a green and brown body, and clear colourless wings supported by small black fibers running through them. I’m totally ill equipped to identify this specimen so I will pass that responsibility on to you. What species is this? It’s pretty big and I’ve seen a couple on the ground in Philadelphia in the last couple of weeks so it can’t be too obscure. The Academy of Natural Sciences in Philadelphia has an entomology department so I’ll ask someone there and keep you updated on the response. In the mean time, if you recognize this insect, let me know in the comments.
What I’m even more interested in is what I found when I put the wing under an AFM. The surface is densely covered with nanoscale bumps about 150 nm in diameter!
The pattern is regular, in some regions approximating a hexagonal lattice. Are these common features of insect wings? What purpose do they serve? Do the bumps reduce the contact area available for the binding of particles making them easier to dislodge? Does the topography control wettability making a surface that is more hydrophobic than would be possible using smooth waxy excretions alone? Hydrophobicity could be a big advantage for insects that want to fly in the rain or that live around water. A film of water could significantly increase the mass of a very thin wing afterall. Does anyone know, or have other ideas?
The varied morphology of insects is fascinating, but most people, myself included, aren’t aware of the finer structure that can’t be seen by eye or even with an optical microscope. I wonder what else are these incredible material scientists hiding…