Humans are confusing. Animals, in comparison, seem easy to understand. Some are even perfectly clear.

Weird Animal Question of the Week wondered: “What are some of the coolest transparent animals?”

Glass Eels

Kids and teens like to look different from their parents, but young eel are winners when it comes to having a distinctive style.

Eels hatch in the open ocean as clear larvae, then go through several stages, including a “glass eel” stage, during which they're the size of a darning needle and “virtually invisible," John Casselman, a professor at Queen’s University in Ontario, Canada, says by email.

In this period, glass eels lack color-producing cells such as chromatophores and melanophores, says George Burgess, an ichthyologist at the Florida Museum of Natural History.

Because glass eels travel long distances in the open water, invisibility helps them survive amid a sea of predators. (See pictures of see-through marine animals.)

For centuries, scientists were mystified by these small, transparent eels, not realizing they were juveniles, Burgess adds.

Green moray eels, like the one in the above video, spawn over huge "and often undiscovered areas," Burgess says, before migrating back to the Western Atlantic coasts of the United States and South America.

Glasswing Butterfly

Butterfly wings are actually made up of scales, or modified hairs, says Katy Prudic, an entomologist at the University of Arizona.

The glasswing butterfly of Central and South America has some brown and white scales, but the clear center of the wing contains hairs that are not scales, covered by a membrane.

That membrane contains tiny structures called “nanopillars” that are randomly arranged, with varying heights. These irregularities prevent light from bouncing off the membrane, according to a 2015 study.

And with see-through wings, the insects are less likely to become tasty treats for predators.

Barreleye Fish

This deep-sea fish also combines camo techniques, with a clear head and a dark body, helping them blend into their lightless environment, Burgess says.

“There’s no need to put evolutionary [effort into] coloration if nobody’s going to see you,” he says.

The fish need to be able to find food, however. Researchers at the Monterey Bay Aquarium Research Institute found that the large, tubular eyes of the Pacific barreleye fish look straight up through its clear head to see potential prey, but are unusual in that they can also look forward.

Glass Squid

Just because you’re clear doesn’t mean you can’t change color.

Most of the 60 species of glass squid are clear, but deep-sea cockatoo squid also have color-creating chromatophores.

Cockatoo squid use these to turn all or part of their body red, a color that “doesn’t show up in the dim blue light of their environment,” squid expert Michael Vecchione of the National Museum of Natural History, says via email. (Related: “This Squid Has Glowing Eyeshadow that Acts Like an Invisibility Cloak.”)

Glass Frog

Central and South America boast 150 species of glass frogs, unique for their front-facing eyes and transluscent undersides.

In 2015, Brian Kubicki of the Costa Rican Amphibian Research Center named a new species of Kermit-like glass frog after his mom.

Its bright green skin blends well into its treetop home, but why glass frogs have a window into their tummies still a mystery.

Still, now Miss Piggy isn’t the only one who can see right through Kermit.

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