Mysteries of invisible animals unraveled

The mysteries of invisible animals unveiled by science: the transparent shrimp and the "glass butterfly" share some fundamental structures.

The power of invisibility has always been in the most recondite desires of human beings: from Tarnhelm, the magic helmet of Wagner's Ring of the Nibelung, to Harry Potter's invisibility cloak, many are the fantasies of objects that allow one to become "invisible".

Some animals, probably unaware of the great human desires, manage to achieve invisibility. This is a particularly fascinating concealment strategy, the subject of two very recent parallel studies.

Butterflies with Glass Wings

The first study is one that appeared in the Journal of Experimental Biology, authored by biologist Aaron Pomerantz of the University of California, Berkeley. The research seeks to determine how the incredible transparent wings of a particular species of tropical butterfly, the Greta Oto, which lives in the forests of Central and South America, develop.

The first encounter with a "glass-winged butterfly," as the Greta Oto is called, Pomerantz says, occurred during a long boat trip in the Peruvian equatorial forest. "I was trying to catch things with a net," recalls the biologist, "and these butterflies simply changed direction and disappeared."

Pomerantz explains the origin of the research, which stemmed from wanting to investigate the particular characteristics of the "invisibility power" of certain terrestrial species. It is in fact quite usual for creatures from the deep ocean to display characters of invisibility and camouflage of the kind, but the phenomenon "is far less common on land."

So the question from which Pomerantz and colleagues' research begins is "What does it take to be able to be transparent on land?"

The particular wings of the invisible butterfly were then analyzed, and they showed peculiar changes "in the shape and density of the microscopic scales that typically make up the colorful patterns of butterfly wings."

The mutation that enables invisibility would seem to be more widespread than one might expect: in addition to lepidopterans, there are also examples of transparency in some particular "glass" frogs, and of course at the bottom of the Ocean.

The Invisibles of the Ocean

Along with the study on butterfly wings, other important data came from the rare sighting, recorded by the Schmidt Ocean Research Institute in the summer of 2021, of transparent octopuses off the Pacific Ocean.

Not only jellyfish, sponges and crustaceans, then, have the gift of invisibility: cephalopods and fish can also display the special feature.

The latest study on the issue is the one published by marine biologist Laura Bagge, of Torch Technologies in Florida, an investigation into the invisibility of the crustacean Cystisoma, a kind of completely transparent shrimp.

The mysterious crustacean, which can reach more or less the size of a human hand, is a particularly fascinating case: "they have a hard shell and are packed with muscle. How is it possible for all this to be transparent?" says the biologist.

Well, it turns out that the Cystistoma's shell has "microscopic irregular structures similar to those found on the wings of invisible butterflies." Such structures, already known in themselves, "have inspired several applications for anti-reflective covers on solar panels and glass."

The muscles of Cystistoma, however, will be the subject of future research by Bagge, as they exhibit entirely different invisibility characteristics. In some cases, however, recalls the biologist, it is particularly useful to have an opaque appearance in the depths of the Oceans: transparency very often, in front of the strange creatures of the deep, can reveal too much about their presence. The crustaceans studied therefore have the power of invisibility but also the eventual antidote: "if a predator emits a blue light at them," explains Bagge, "they immediately expose a pigmented shell that can absorb the light."