The glass frogs are one of the strange but captivating creatures in the world. When you look down at this creature, you might initially notice its soft lime-green color but when you turn it over, your attention would be caught by the appearance of its abdomen. Guess what! The stomach of this creature is transparent, just like the name implies – a glass frog.

If you closely examine Glass frogs, you would visibly notice the visceral organs, including the heart, liver, gut, and lungs. You can easily observe the way its heart pumps blood throughout its body and even the way the food digests. A glass frog is also referred to as a ‘see-through frog’ because of their translucent skin. More than 120 species of glass frogs exist in about 10 genera.

Glass frogs’ habitat

  • Glass frog facts
  • Glass frog stream habitat in Santa Elena Reserve near Monteverde, Costa Rica
  • The heart of the MLC rainforest in the Peruvian Amazon is a home to glass frogs

Glass frogs are usually found in warm climates in Central and South America. They occur from tropical lowland forests to mid-elevation mountain forests. Most species of glass frog are small in size, with the adults ranging from 20 to 30 mm (0.8 to1.2 inches) long. In just a few species, the adults are larger, attaining a maximum length of nearly 3 inches (80 mm). 

Why Glass frogs are endangered

  • Deforestation is forcing the Glass frogs to leave their natural habitat
  • A Glass frog captured in Germany.
  • The three Glass frogs that were found after 18 years now reside at a national park in Bolivia

The Northern glass frog was once the most abundant species found in Central and South America. Glass frogs are endangered sometimes due to their small size. They are an easy target for many predators, including snakes, mammals, and birds. Glass frogs are arboreal animals, as they spend most of their time on trees. They have become endangered due to habitat loss from human activities and deforestation. According to BBC, this rare species of frog was seen in Bolivia for the first time in 18 years.

 Here are a few interesting facts about a glass frog:

1. They spend their lives on the trees

  • A Glass frog captured in Sarapiqui region, Costa Rica.
  • A Glass frog clinging to leaves
  • A granular Glass frog at the Monteverde Frog pond, Costa Rica

Spending their lives on the trees means that they are arboreal animals. They only come to the ground when it is the season for mating. As mentioned earlier, this is why they have become endangered due to habitat loss. 

2. Glass frogs are hard to spot by predators 

  • Glass frogs illustrating a new mechanism of camouflage
  • A Glass frog with round, sticky toe pads blends into a leaf

Glass frogs are usually bright green or olive green in color and are hard to spot. Because of the color – green, it is believed by some scientists that predators would find it more difficult to locate and prey on them. The translucency of the frog is a form of camouflage, which makes the edge of the frog softly blend with its surroundings. The line which separates the color of the frog’s skin from its environment is softened and this is referred to as ‘edge diffusion‘. Be it a light or a dark surface glass frogs are a pro at hiding.

3. Glass frogs are carnivorous 

  • A glass frog swallowing a snake
  • A reticulated Glass frog

Glass frogs eat flesh. They eat lots of different kinds of spiders and other insects. The way glass frogs feed has not been well researched yet. But according to researchers, they appear to consume arthropods and small insects. Glass frogs have been seen hunting insects in the dense vegetation beside tropical rivers. When glass frogs are captured by scientists they are often fed fruit flies.

4. They come in different sizes

  • A tiny glass frogs sits on top of a thumb in Choco, Columbia.
  • tiny glass frogs
  • Some glass frog species are really tiny
  • Spiny glass frog from Limon Province, Costa Rica.

Depending on the species, glass frogs come in different sizes. Smaller species may be less than 1 inch in length, but larger species maybe about 3 inches long.

5. They are nocturnal animals

  • Glass frog at night at the lowlands of Costa Rica
  • Glass frogs photographed at night with a flashlight

Because Glass frogs are active at night and prefer to come out at night, they are referred to as nocturnal animals. 

6. Glass frogs are territorial animals

  • Two male cascade Glass frogs locked in territorial combat
  • A Glass frog standing guard over its eggs.

Whenever their territory tends to be occupied, the male Glass frogs alert others by vocalizing. They together ward off all the uninvited visitors. In a situation whereby this intruder refuses to leave, the males in the territory exhibit aggression and vehemently chase away the unwanted males. 

7. Glass frogs have expanded digit tips that help them in climbing

  • A Glass frog climbing a leaf near central Costa Rica
  • A Glass frogs expanded digits help them climb shrubs easily
  • A glass frog showing off his toe pads

The expanded digits of Glass frogs give them the ability to live in trees or shrubs along forest streams.

8.  They usually mate only after the rainy season 

  • Two Glass frogs mating.
  • The Glass frogs have transparent eggs, where the heads and tails of developing tadpoles can be clearly seen inside
  • Glass frog eggs

After raining season or during the light showers, the male Glass frog hangs on a leaf above water for mating. But before the mating occurs, the male has to first call the females. Furthermore, the males who call, sit either on the streams of the topside or underside of the leaves. When the females arrive, the mating takes place on the leaf, and that is where she lays her egg. Surprising right? Female lays between 20 and 30 eggs on the underside of the leaves. 

9. The male protects laid eggs

  • La Palma Glass frogs - a female, male, and their eggs.
  • A transparent egg mass with developing Glass frog tadpoles
  • A young emerald Glass frog

When the female Glass frog departs after laying eggs, the male has the job of protecting the eggs from predators. Some males even attract more females for mating and hence have different groups of eggs to look after. After two weeks, tadpoles hatch into the water. Pending the period for metamorphosis into froglets, tadpoles feed on leaf-litters and detritus at the streamside. One of the major egg predators is “frog flies” which lay their eggs on the egg masses. Their eggs hatch quickly, and the maggots feed on the frog embryos. Some species of glass frogs do bury themselves in the ground until they develop into adult frogs, whereas other species undergo metamorphosis in the water. 

10. Glass frogs have unique pigment cells in the skin that reflects infrared radiation

  • Glass frogs have unique pigment cells in their skin, helping them to camouflage effectively
  • The Fleishman's Glass frog showing the background through its transparent flesh.

This pigmentation possessed by glass frogs provides them with camouflage property when they sit on leaves, thereby shielding them from predators, including snakes, birds, and pit vipers. 

These small and rare Glass frogs have tons of supercool secrets to reveal. From the trick pattern on their skin to their see-through belly, these small and cute creatures are limited to the rainforests of Panama, Columbia, Ecuador, and Costa Rica. Around 77 species of Glass frogs are threatened with extinction due to a sudden increase in their illegal international trade. The WCS has been working for almost 10 years to conserve the habitat and the ecosystem where these unique amphibians live.

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