The Dark Side

What could possibly be more alien than a creature with big, bulging black eyes and green transparent skin...skin through which you could see it's bones and internal organs?

The amazing glass frogs are true gems, some of the most beautiful  and delicate creatures you will encounter in a Tropical Rainforest. They are so fragile, in fact, that the direct hit of a large raindrop may be enough to kill one!

 Because Glass Frogs tend to inhabit streams, it is uncommon for us to encounter them on The Night Tour. About 140 species of glass frog have been identified, 65 of which were just discovered between 1989 and 1998. All glass frogs make their homes in Central and South America. Costa Rica has a total of thirteen species. Throughout the streams and rivers of the Osa Peninsula, scientists have identified six glass frog species. Each Glass Frog species found in Drake Bay has its own page on this website.   

Glass Frogs are typically tree dwellers and it is rare to see one on the ground. Their green, translucent skin makes the frogs virtually undetectable when resting quietly on a leaf. This superb camouflage also gives the frogs an edge when hunting the small insects and flies they prey on. Forward facing eyes, which distinguish glass frogs from other tree frogs, give them binocular vision. Good vision, coupled with incredible camouflage and feline agility, make this unassuming little frog a formidable predator.

Glass Frogs are mostly nocturnal and are most active in rainy or very humid conditions. At this time, males call from their perches, hoping to lure in a female. If a female approaches a calling male, the two will join in amplexus and will lay their egg clutch  on the tip of a leaf overhanging a stream. After about two weeks, the little tadpoles will squirm from the eggs. This is often triggered by a heavy rain. They fall into the stream and feed on organic matter they scavenge from the bottom. This stage of their metamorphosis may last several months and virtually nothing is known about it. In fact, the tadpoles are still unknown in 6 out of 13 Costa Rican glass frog species.

When the young frogs leave the water, they are minute. In some species as small as 16 millimeters. We found the frog pictured above after a Night Tour in the vegetation near a stream by our home. You can see how tiny it is compared to Tracie's fingers in the photo. It still had it's tadpole tail and had probably emerged from the stream that night. Click on the picture for a close up shot.

Finding glass frogs, even in the best of conditions, is always challenging. One thing is for sure, you are going to get wet. These frogs often occupy the vegetation overhanging streams and are most active on rainy nights.

Many sit on top of leaves while calling, making them difficult to see from below. Their small size and perfect camouflage make it even more difficult.

It's easy to understand why much of their lives remains a mystery to science.

For us, every time we encounter a glass frog it is a special occasion and we consider ourselves very fortunate. All of the glass frogs featured here were encountered and photographed in the wild on the Osa Peninsula.

Precious little information is available on the natural history of glass frogs. This site is indebted to Brian Kubicki's wonderful publication Costa Rica Glass Frogs, the first detailed book ever written about these amazing amphibians.  It will undoubtedly prove invaluable to anyone interested in learning about glass frogs.

References:

Kubicki, B.  2007  Costa Rica Glass Frogs  Editorial INBio

Leenders, T.  2001  A Guide to Amphibians and Reptiles of Costa Rica  Zona Tropical

Savage, J.  2002  The Amphibians and Reptiles of Costa Rica   University of Chicago Press