Glass Frogs of Costa Rica

Costa Rica is among the most biodiverse places on the planet. The country’s animal life is exotic, tropical, brilliant, unique and captivating. This fame covers the local Poison Dart Frogs – but often overlooks the equally captivating Glass Frogs. With their translucent or even transparent skin (hence the name) and striking coloring, these arboreal amphibians have finally made it to the pages of our blog.

SEE-THRU AMPHIBIANS

Most Glass Frog species are lime green in color and wear sections of a translucent or even transparent skin – you can see right inside their bodies. Organs like the beating heart, liver, kidneys, intestines and blood vessels become visible – and we may have a faint idea of WHY nature, evolution and natural selection has decided that transparent skin is an advantage.

WHAT IS THE REASON FOR THE TRANSPARENT SKIN?

Nature does not act without reason. Every trait – whether physical or behavioral – exists to aid the reproduction and survival of the specie. NOTHING in nature is an accident. So as it goes, there must be a very good reason for the Glass Frogs’ partial translucency & transparency, that much we knew. But for the longest time, we couldn’t quite figure it out – the obvious answer was ‘camouflage’ but under differing lighting conditions it seemed that the attributes were not that effective as regular camouflage successfully employed by many other frog and animal species.

We also knew that other than general translucency, the frogs also had more or less opaque backs and usually very translucent legs and fingers – and therein lay the key. The opaque backs, more translucent bodies and nearly transparent legs & fingers create a sort of gradient which makes the edges of the frog blurry & less defined, and therefore masks the frogs’ true shapes. Add to that the lime green coloring, which blends with leaves and plants, and you’ve got a much more effective camouflage system.

This weird camouflage phenomenon, in which the frog’s edges are softened to match the relative brightness of its surroundings, is referred to as edge diffusion. And if that was not enough – when resting or threatened, Glass frogs have a fascinating ability to conceal their red blood cells which enhances their transparency. Their livers are coated with a reflective guanine crystals, which helps scatter light and obscure the red color of their blood cells. By directing most of their red blood cells to the liver, the Glass Frogs reduce the amount of visible pigmentation in their bodies, making them appear even more transparent.

COSTA RICAN GLASS FROG SPECIES

14 species of Glass Frogs call Costa Rica home – and more are being discovered, so the true number is very likely much higher. Here we present a few of the best-researched and known examples:

BARE-HEARTED GLASS FROG or KERMIT FROG – Found in central and south-eastern Costa Rica, these frogs have the most transparent bellies of all Glass Frog species. This specie has only been discovered, in 2015, in the Talamanca Mountains of Costa Rica – and it got world-famous attention due to its resemblance to Kermit the Frog.

STARRETT’S GLASS FROG – Found in humid mountain forests around Costa Rica, especially around the central spine. It is threatened by habitat loss in its range area

YELLOW-FLECKED GLASS FROG – Found in Costa Rica at elevations up to 1,500 meters. This hardy Glass Frog can survive along streams in altered habitats such as pastures, orchards, and even towns and cities.

SAN JOSE COCHRAN FROG – This Glass Frog can handle altitudes up to 2,000 meters. Unfortunately, it has not been seen in Costa Rica since 1986 – an we don’t know why, despite numerous survey efforts to locate the species.

FLEISCHMANN’S GLASS FROG – The most populous and common of Costa Rica’s Glass Frogs, this specie lives in low and mid-altitude wet forests.

EMERALD GLASS FROG – These frogs prefer to live amongst mature old growth forests. While not under threat as a specie, the Costa Rican Monteverde population has recently collapsed – however the frog remains common in other areas of Costa Rica.

SURETKA GLASS FROG / STRIPED BACK GLASS FROG – Preferring lowland forests up to 600 meters in elevation, these frogs are not deterred by degraded habitats. The frog is named after the Suretka locality in Talamanca, Costa Rica, where can be found.

LIMON GIANT GLASS FROG – Named after a part of its range – Limón, Costa Rica – this frog is also known as Holly’s Glass Frog and Ghost Glass Frog.

GRANULAR GLASS FROG – Their grainy skin, which can range through several colors, helps the frogs increase the potency of their camouflage.

POWDERED GLASS FROG – Rather rare in Costa Rica, these frogs prefer low forests, sometimes no higher than 300-900 meters, depending on the population. They can survive in disturbed habitats.

THE LIVES OF GLASS FROGS

Glass Frogs are very small, rarely exceeding 1 inch (2.5cm) in length. So small, in fact, that they are know to have died from raindrop impacts! They are found in Central and South America, preferring to live around streams and rivers of lowland and mountain rainforests – however some species have become comfortable with life in disturbed habitats such as pastures, parks, and even towns and cities – as long as portions of habitat are available. They are active at night and the best way of knowing whether Glass Frogs live in your backyard is to listed for their nightly calls.

Glass Frogs are arboreal, meaning many species spend most of their lives in the trees. They prefer the safety of the jungle canopy as there are many more predators on the surface as opposed to the heights of jungle trees. However they make their way to the ground during mating season – the males venture to the forest floor to find mates, and the females attach eggs to the underside of a leaf that is hanging over the stream. The males of most species guard the eggs until they hatch while the females have been known to brood the eggs shortly after laying them. When the tadpoles hatch, they fall into the waters below – and this is where the parental care ends. The tadpoles are strong, with a powerful tail and low fins – this is an adaptation for fast flowing mountain streams.

Glass Frogs are carnivorous, making a meal of crickets, moths, flies, spiders, and even other smaller frogs. They themselves fall prey to fish, birds, snakes, lizards, bigger frogs, and predatory insects like spiders. Their eggs are vulnerable to many predators including certain species of flies which infest the eggs with predatory maggots. However the eggs are still much safer stuck to the underside of a leaf as opposed to being laid in the water where fish, shrimp, insects, even snakes, birds and various mammals  could have a proper feast.

Glass frogs produce high-pitched calls that are often described as chirping or whistling. These sounds are typically used by males to attract females during mating season, but many species vocalize year-round. Their calls can vary depending on the species but they are generally soft and melodic, blending well with the ambient sounds of their rainforest habitats.

THREATS

Four of the five major threats threats to the little Glass Frogs are caused by humans: deforestation, invasive species, pollution, and illegal pet trade. Because frogs breathe through their skin, they are super sensitive to both air and water pollution. These many threats have led to a decline in the population of this species – but there is another culprit – an illness called Chytridiomycosis, caused by a fungal infection. While a natural pathogen, human activity does contribute to its spread around the world.

CHYTRIDIOMYCOSIS

Chytridiomycosis has been tied to the sharp decline or even extinction of frog species around the world. The fungal pathogen responsible can lead to isolated deaths in certain populations while completely wiping out others. Unfortunately, no effective methods have been developed to manage the disease in the wild.

While some strategies for combating the fungus exist, none have proven viable on a large scale. This disease is considered a major factor in the global amphibian population decline, impacting roughly 30% of species worldwide. Findings highlight international pet frog trade as a pathway for the fungus to invade native ecosystems.

GLASS FROGS ARE AMAZING – AND THE FACT THAT THEY ARE NOT WELL-UNDERSTOOD ADDS TO THE ALLURE

Glass Frogs are very small and can be hard to find and study – because of this, there are many sizeable gaps in our understanding of many species. Many Glass Frog species live in remote, dense rainforests, making them challenging to observe. Their exact population sizes, behaviors in the wild, and even some of their ecological roles remain elusive. Continually, new species of glass frogs continue to be discovered.

So keep a keen eye – if you know that Glass Frogs are around because others have seen them or you have heard them chirping at night, why not set off on a frog-finding expedition? Kids would especially love finding a real-life Glass Frog, best after sunset with a flashlight in hand. But since they are so small and fragile (there are reports of them being killed by raindrops) make sure you do not handle them and enjoy them from a safe distance!

RESOURCES

• Costa Rica Amphibian Research Center – https://cramphibian.com/
• Veragua Rainforest Article – https://truewindhealingtravel.com/costa-ricas-veragua-rainforest-ecotourism-and-frogs/

Do you dream of living in the midst of breathtaking tropical scenery and amongst amazing animals like the cute & captivating Poison Dart Frogs? At RE/MAX WE SELL PARADISE, we list hundreds of tropical properties – homes, land, farms, estates & businesses – all within a stone’s throw of the amazing rainforests, mountains, beaches and resident exotic animals that make Costa Ballena a world-famous destination. Start your journey to paradise by browsing our property listings here.

Cover photo c/o Ivan Rojas, Pexels