In my free moments at the California Academy of Sciences, looking through drawers of natural history specimens and ogling all the amazing insects, there is one drawer….ONE DRAWER…that always makes my eyes shine like Indiana Jones in a secret treasure chamber…Behold the mighty, tiny, Pachyrhynchus weevils:
With rainbow-hued swirls, metallic stripes, and turquoise polkadots, it’s easy to imagine someone painting these intricate and colorful weevils with a very small paintbrush. That’s why here at the Academy we affectionately refer to the dozens of weevils in the Pachyrhynchus genus as “Easter egg weevils”.
Each species of Easter egg weevil has their own unique pattern and color. Take a look – chances are you will get the urge to fill up a tiny basket with them!
Unlike easter eggs, Pachyrhynchus weevils are mobile, but they don’t move around very fast! In Taiwan and the Philippines, they can be found bumbling around their rainforest habitat, munching on leaves, and generally looking fabulous.
But behind those shining colors are some truly amazing optical tricks. Look closely at the colored patches, can you see the sequin-like scales?
Much like the scales on a butterfly’s wings, the colorful bands and patches of iridescence on Pachyrhynchus and some other genera of weevils come from scales that are layered on the outside of their exoskeleton, like shingles on a house.
Within each scale there are very small (nanometer-sized) structures that refract light of different wavelengths. Some colors, like red, have long wavelengths, while others, like blue, have short ones. The way the different wavelengths of light in the visible spectrum interact with the nano-sized structures inside the weevils scales determines which wavelengths are absorbed and which are reflected, and therefore determines which colors we see glittering off of them.
These are what scientists refer to as structural colors, and these Pachyrhynchus weevils have got em’ for dayz!
But scientists have discovered that some weevil scales not only look like gems, they act like them too.
Photonic crystals are an ordered arranegement of nanostructures that have the ability to direct photons of light in a selective and predictable pattern. Diamonds are a great example, opals come pretty close, BUT some living organisms possess nanostructures that are arranged like a photonic crystal as well.
When photonic crystals are organized in one dimension they create the metallic and polarized reflections of, for example, the skin of cephalopods and fishes, the elytra of jewel beetles, scarabs, and the breast feathers of birds of paradise. Two-dimensional photonic crystals create the coloration of peacock feathers (along with pigmentary colors).
THREE-dimensional photonic crystals are rare in nature. But the scales found on some insects have them, including…you guessed it…Pachyrhynchus weevils!
Pachyrhynchus argus looks like it is covered in bejewelled cheerios, but it is on the microscopic level that this species really shines. It turns out that their scales contain structures that resemble the structure of opals. Synthetic opal is currently very hard to manufacture, but these guys make it to perfection.
In the IN-famous words of El Guapo, “That’s a good trick!”
But the most coveted type of photonic crystal is one structured like a diamond. Because this type of crystal can reflect a wide band of colors, has high reflectivity, and is better able to control the flow of light through it, scientists hope to use it to develop more-efficient solar cells, telecommunications, optical computer chips, and basically all manner of tiny electronics.
Synthesizing a 3-D photonic crystal with this shape is currently extremely difficult.
Entimus imperialis, otherwise known as the Brazilian Diamond Weevil, is covered in rows of brilliant spots on black elytra. They certainly look like diamond-encrusted jewelry pins, and as it turns out, the scales inside each of the concave pits contain large areas of three-dimensional photonic crystals, shaped just like a diamond!
Real diamond is formed when carbon is subjected to extremely high heat and pressure miles below the earth’s surface, so it’s not exactly the same, of course. But the scales of Entimus imperials – an ordered, three-dimensional lattice of chitin in a diamond shape – could be the key to learning how to manufacture structures like this.
These amazing weevils are just a franction of the over one million species of insects and roughly 60,000 species of weevils described to science. With the estimated millions more insects to be discovered – shiny ones, cryptic ones, big ones, small ones – who knows what we have left to learn from their fascinating biology.