Members of the Centrolenidae family are known as "glass frogs" because their abdominal skin is often translucent, allowing a close observer to see their internal organs at work. Cochranella granulosa, or the grainy Cochran frog—also known as the crystal frog—gets its name from the fine, particulate quality of its skin, which is tinted dark bluish-green with black spots.
Cochranella granulosa is arboreal, living in trees in the sticky, humid forests of South America. It keeps a decidedly low profile, and even when it’s out, it’s sooner heard than seen: males are known to emit a harsh and persistent creaking call to advertise themselves to potential mates, often calling as loudly as they can to drown out rival suitors. They can be belligerent as well, especially when it comes to defending an ideal streamside mating spot: territorial disputes—in which two males hang upside down from neighboring leaves and grapple chest to chest—can last up to two hours (and have been likened to sumo wrestling matches).
Like all glass frogs, the grainy Cochran frog is most active at night, which—along with their bodily transparency—makes it hard to spot for predators and sightseers alike. During daylight, it blends in easily with the flora of the rainforest, especially when flattened against leaves. Consequently, much of what we know about its behavior is based on times when it comes out to mate and breed.
Range and Conservation
The grainy Cochran frog dwells in the humid and sticky lowlands of Panama, Nicaragua, Costa Rica, and Honduras. Its population is threatened by habitat loss, deforestation, and pollution, but it's hardy enough to remain in high numbers throughout South America, earning the “least concern” classification from the IUCN for now.
Distinguishing Glass Frogs
The transparent skin of glass frogs does more than just offer a real-time internal diagnostic for a close enough viewer. It also helps distinguish some of the dozen or so species in the Centrolenidae family based on an unlikely factor: bone color. The grainy Cochran frog has dark green bones, as do cousins like the Pichincha glass frog and the Pacific giant glass frog, whereas species such as the Atrato and La Palma glass frogs have white bones.
Eggs on Leaves
Males are so fussy about defending their mating spots because glass frogs lay their eggs in a very particular way: in a gelatinous clutch on leaves overlooking a stream. The leaf tip provides a constant flow of water over the eggs while shielding them from sight. About two weeks later, larvae hatch into tadpoles and at the next rainfall drop into the stream below, where they will spend several months growing into frogs.