Overview
The Bare-hearted Glassfrog (Hyalinobatrachium colymbiphyllum), also known as the cricket glassfrog, is an astonishing jewel of the Mesoamerican rainforest. Perched on the underside of smooth leaves overhanging bubbling mountain torrents, this translucent emerald anuran is world-famous for its crystal-clear ventral window. Unlike other glassfrogs whose internal organs are partially obscured by opaque white peritonea, the bare-hearted glassfrog has completely transparent pericardium and belly skin, allowing observers to see its red heart beating vigorously in real time.
Biology and Physical Characteristics
Hyalinobatrachium colymbiphyllum is a small, delicate treefrog sporting an apple-green to pale lime dorsal surface sprinkled with minute yellow flecks that perfectly mimic mossy liverworts or drops of morning dew. Its bones are pale green due to biliverdin deposits. The ventral surface is an anatomical marvel: completely devoid of guanine pigments, the skin is crystal clear, offering an unobstructed window into its internal anatomy. The red beating heart, aortic arch, digestive tract, liver, and golden gallbladder are fully visible in living, breathing individuals. Its irises are golden-yellow, housing horizontally elliptical pupils.
Behavior and Ecology
Nocturnal and strictly riparian, males establish territories on the undersides of leaves suspended 1 to 5 meters above cascading rocky streams. At night, they emit high-pitched, insect-like trills that sound remarkably like crickets. Females lay a jelly-encapsulated clutch of 50 to 75 bright green eggs on the leaf underside. After fertilization, the dedicated father demonstrates extraordinary paternal devotion: he perches directly over the egg clutch every night, protecting the embryos from predatory wasps and hydrating the clutch with his bladder water until the tadpoles hatch and drop straight into the rushing stream below.
Conservation and Human Impact
While evaluated as Least Concern by the IUCN due to healthy populations across protected areas in Costa Rica and Panama (such as Corcovado and Soberanía National Parks), the bare-hearted glassfrog is highly vulnerable to habitat alterations. Because its tadpoles require clean, well-oxygenated, unpolluted stream water, agricultural siltation, pesticide runoff, and riparian deforestation quickly wipe out local breeding colonies. Protecting clean river corridors and maintaining intact primary forest buffers are vital to securing this living anatomical wonder.
Interesting Factoid
The skin on the underside of the bare-hearted glassfrog is so completely transparent that you can watch its bright red heart pumping blood and its digestive system working without touching or harming the frog in any way.
Last updated: October 2026