October 1, 2026, 12:05 pm | Read time: 4 minutes
Some animals hide from predators by simply becoming invisible. From frogs to fish to jellyfish: PETBOOK presents eight animals whose bodies are completely or partially transparent–and explains why transparency is much rarer on land than in water.
Why Are Some Animals Transparent at All?
For a body to appear transparent, it must barely refract or reflect the light that hits it. In water, many animals achieve this surprisingly well because the transition between water and animal tissue makes only a small optical difference. Light is hardly scattered there.
At the boundary between air and tissue, however, this effect is much stronger, which is why there are very few transparent animals on land, such as the delicate wings of some dragonflies or butterflies. Additionally, red blood with a lot of hemoglobin is hardly transparent. This is one reason why transparent vertebrates on land are a real rarity.1,2
1. Glass Frog
The glass frog (Centrolenidae) lives in the rainforests of Central and South America and is inconspicuously green on its upper side. Turn it over, and it becomes spectacular. Through the transparent belly skin, you can observe the heart, liver, and intestines at work. Researchers at Duke University discovered in 2022 that glass frogs become even more transparent while sleeping by temporarily “hiding” up to 89 percent of their red blood cells in the liver.
This allows their tissue to let significantly more light through. It’s a clever trick to be as inconspicuous as possible on a leaf during the day while they sleep and are particularly vulnerable.3,4
Also interesting: Glass Frog: Researchers Solve the Mystery of the Transparent Animal
2. Glasswing Butterfly
The South American glasswing butterfly (Greta oto) is one of the few butterflies with transparent wings. While the outer edges are orange-brown to black, the inner surfaces completely lack light-reflecting scales–they appear glass-like. This feature helps the diurnal butterfly hide from sharp-eyed birds even in flight.5
3. Barreleye Fish
The barreleye fish (Macropinna microstoma), also known as the spookfish, lives in the dark depths of the Pacific. Its head is surrounded by a transparent, fluid-filled shield through which you can see the animal’s tubular, upward-facing eyes.
When the fish is brought out of the water, this often destroys the delicate shield. Marine biologists suspect it protects the eyes from the toxic stingers of jellyfish, which the barreleye fish feeds on.6
4. Crocodile Icefish
A true exception among vertebrates is the Antarctic crocodile icefish (Channichthyidae). Its blood is not red but almost transparent because these animals are the only known vertebrates completely lacking the red blood pigment hemoglobin. This is made possible by the extremely cold, oxygen-rich environment of Antarctica. There, the fish can absorb enough oxygen from the water even without hemoglobin.
Also interesting: From the Chocolate Dwarf to Beyoncé–These Animal Species Really Exist
5. Glass Squid
Around 60 species of glass squid live up to their name: Many of them appear almost completely transparent. This keeps them hidden from predators when they inhabit partially sunlit, shallow waters. To make their digestive gland as inconspicuous as possible, the animals usually hold their bodies vertically in the water. Even the colossal squid, the largest invertebrate on Earth, is still mostly transparent and only a few centimeters long in its juvenile stage (PETBOOK reports).7
Also interesting: Which Jellyfish Are Dangerous in the Mediterranean?
6. Box Jellyfish
The box jellyfish (Chironex fleckeri) is considered the most venomous animal in the world and is also nearly invisible. Its bluish bell can grow up to 30 centimeters, and its tentacles can individually reach up to three meters long. Because the box jellyfish is hardly visible in the water, it is often noticed too late. This is also one of the main causes of dangerous encounters with swimmers in the Indo-Pacific region (PETBOOK reported).
Also interesting: This Almost Invisible Animal Is Considered the Most Venomous in the World
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7. Sea Angel
Sea angels, also known as sea butterflies, are transparent sea snails that have two wing-like swimming organs instead of a foot, allowing them to gracefully “fly” through the water. Their transparency makes them much harder for predators to spot in the open sea, where there are few places to hide.
8. Tardigrades
Tardigrades are among the most resilient creatures ever: They survive without a heart, lungs, or circulatory system and instead breathe through their skin. Fittingly, their blood is also transparent (PETBOOK reported). These microscopic creatures withstand extreme cold, heat, and even space, making them one of the most remarkable examples of how transparency is utilized in the animal kingdom.