Let’s imagine a walk through the tropical jungle of Central America, the warm breeze blowing across your face and your anticipation for the creatures that might cross your path. Suddenly, a shiny object hangs from the leaves of the bushes, but it is not a hidden treasure, although it appears to be made of silver; It is the silver beetle, an insect that has caught the attention of more than one for its metallic appearance.
We often believe that most of life is divided between mammals and reptiles, however, insects are actually the most abundant group of beings that inhabit the Earth. It is to be expected that among their ranks you can find a variety of surprises of different appearances. For example, we have the popcorn insect that seems to have sprouted from a corn seed or the Picasso insect that lives up to its name and is a true work of art.
silver beetle
But among its more than 900 thousand species, there is an insect that has earned the admiration of those who have had the fortune of crossing paths with it. This is the silver beetle that stands out for its reflective ability, which gives it a metallic appearance and appears to be made of silver.
Credit: David Pascual.
The species was first described in 1894 by zoologists Walter Rothschild and Karl Jordan. Although it was initially named Plusiotis limbata, its scientific name later changed to Chrysina limbata. Today very little is known about the metallic insect, but its home has been identified in the rainforests of Central America, from Costa Rica and to southeastern Mexico.
The extraordinary beetle is of average size, measuring between 2.5 and 3.5 centimeters and like all its beetle congeners, it reproduces by means of eggs that the female places in the roots of the plants. They then go through the process of metamorphosis, that is, they first become larvae and later transform into pupae and finally obtain their final form of reflective beetle.
Dielectric mirrors
Not much is known about the mechanism that gives the silver beetle its metallic appearance, but entomologists believe that the reflectance is achieved through the interference of a thin film within the layers of a compound called chitin, a long-chain polymer derived from of glucose.
These layers of chitin coating are in turn squeaked, meaning that they act as a dielectric mirror with gaps of variable depth, which are capable of reflecting different wavelengths depending on the depth of the film.
The result is a beautiful mirror capable of almost entirely reflecting the light that comes from the sun and that is why it acquires its characteristic metallic color. It is so surprising and literally works like a mirror, that in the photographs of silver beetles that have been taken, you can see the photographer reflected in the insect’s shell.