Biologists Unlock the Secrets of ‘Invisible’ Animals

This story was originally published on Atlas Obscura. It is part of the Climate Desk collaboration.
Aaron Pomerantz, a biologist, saw tiny invisible jets zipping along the trail while trekking through Peruvian rain forests. It was an eight-hour boat trip from the nearest jungle settlement. He said that he was out there trying to catch the insects with a net. But they just changed directions and disappeared.

Clear-winged butterflies were his first encounter. These insects are native to Central and South American forests. They have remarkable camouflage methods: they can be seen through or even glass their wings, making them difficult to spot in dense understory.

It's almost like invisibility. This is Pomerantz's lead author of a study published in the Journal of Experimental Biology. The study examines the development of clear wings. It's much harder for predators not to find you if you have an invisibility costume. There are many transparent species in ocean environments, but it is much more common to find them on land. This really brings up the question: What is it like to be transparent on land, and what does it mean?

Pomerantz, his colleagues from Caltech, the Marine Biological Laboratory (Woods Hole) and the University of California Berkeley studied the wings of Greta oto (also known as the glasswing butterflies). They discovered a few key factors. The microscopic scales can be modified in order to create butterfly patterns. An extra antiglare layer can be added by tiny waxy pillars.

It is not a singular adaptation. Pomerantz says that this adaptation has been adapted many times. He notes that there are hundreds of species of glass-winged butterflies and moths. They make up the majority of rare cases of transparency on land, even though they are only a small part of the Lepidoptera order. Another example is the glass frog, which has varying degrees skin transparency.

On the other hand, the ocean is full of see-through species. These include jellyfish, sponges, crustaceans and cephalopods as well as fish. Two rare sightings were made earlier in summer 2021 of a glass Octopus during an expedition aboard the Schmidt Ocean Institutes research vessel Falkor to the waters off the remote Phoenix Islands in Pacific Ocean. It turns out that being invisible is easier in the ocean than it is on land due to the physical and visual properties of water.

It can be compared to a piece glass floating in water, according to Laura Bagge, a marine biologist. This environment is far less feature-rich than on land and doesn't have to contend with gravity. These animals are mostly watery and buoyant creatures, with no backbones or dense structures necessary to survive on the ground.

Imagine the classic Jaws scene, where a swimmer stands in front of the sun streaming down from above. Transparency helps you get by underwater predators who can see opaque shapes easily when the sun shines. Bagge says that even deep in the ocean, it is still useful as a lot of bioluminescent animal emit light.

Bagge, now a senior biologist at Torch Technologies Florida, became interested in animal transparency while on a research cruise to complete her Duke University dissertation. Bagge had reached for a bucket of sea animals and found a strange specimen. She said that it was hard like a lobster but was actually a clear animal. It was Cystisoma, a shrimp-like crustacean that can grow to as big as a person's hand. Because they are so cool, they have a hard outer shell that is packed with muscle. How can you make this clear?