truly bottomless black can be found in colorful places. Two such examples have been introduced before, namely, some species of birds of paradise and peacock jumping spiders. The males of these animals rely on bright body colors and very interesting dance movements to attract the attention of females, and right next to those bright colors, there are super-dark areas that are darker than black. They are so dark that they seem to lose details, and their reflectivity to light can be as low as 0% or even 0%, which is about to catch up with the light absorption effect of man-made ultra-black materials.

(an old friend of the animal emoji circle, a gorgeous male bird of paradise that is too dark to see the bottom)

and a similar natural super-black structure also exists in some species of butterflies. For example, in the four species pictured below, the bright spots of the males are also set off by the surrounding ultra-dark areas, where the light reflectivity can be as low as 0.06%.

(several species of butterflies with very dark wings, source: Richard Stickney, Museum of Life and Science)

how to make it too dark to see the bottom? All kinds of natural and artificial ultra-black materials rely on microstructure that "traps" light, in which light is reflected many times and gradually absorbed. Last week, a study analyzed exactly what the ultra-black structure on butterfly wings looks like. Here are the electron microscope images in the study:

(source: Alex Davis, Duke University)

this shows the scale structure of the ultra-black part of Trogonoptera brookiana. Compared with ordinary butterfly scales, these scales have smaller and deeper holes on the surface, which are responsible for "trapping" light. According to the report and the paper, it is necessary to carry out thin gold plating on the surface of the sample when preparing the electron microscope sample, but the ultra-black part still looks very black even after this treatment, which shows that the light absorption effect of these microstructure is really good.

researchers will use the super-black structure of nature as a source of inspiration for the design of artificial materials. Butterflies' ultra-black scales are no better than artificial carbon nanotube materials, but they are more durable and thinner.

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as for the effect of ultra-black scales on butterflies, it should be similar to that of birds of paradise and jumping spiders, and is related to sexual selection. The deep black can make the colorful parts of the male more conspicuous, so that it is easy to get a partner.

Source: https://www.nature.com/articles/s41467-020-15033-1

https://www.eurekalert.org/pub_releases/2020-03/du-tmu031020.php