The fringe-limbed treefrog we are talking about here is definitely an oddball. It lives high up in the trees of the cloud forests of a mountain range in south-eastern Mexico. These are two factors that make it seem rather unusual. First of all, when we think of creatures living high up in trees, we tend to think of birds rather than frogs. And not without reason, because frogs are amphibians and, as such, are by definition bound to water – ‘Amphibian’ comes from the Greek “amphibios”, which means ‘double life’ and alludes to the fact that amphibians commute between the worlds of water and land habitats, with their larvae initially breathing through gills and later metamorphosing into air-breathing adults, as well as their lifelong close connection to the wet element. However, as we know, bodies of water tend to be found on the ground. So if you live as a frog at lofty heights, you have to come up with some evolutionary solutions to overcome this distance or develop alternatives to the classic frog pond. If you also live in the cloud forests of a mountain range, you are practically on an island, because the price of specialisation is that you are increasingly tied to your very specific niche. It is cool in the cloud forest, while down in the tropical lowlands it is notoriously hot and humid, so you stay among your own kind and lose contact with others, which in turn reinforces the development of peculiarities: speciation.

The Lichenose Fringe-limbed Treefrog seems to live exclusively on the mountain slopes around the San Martín volcano, presumably only at altitudes above 1,000 metres. ‘Presumably’ indicates that we don’t know for sure, because, as already mentioned, hardly anyone has ever seen these frogs in the wild. In fact, scientists are only aware of a handful of specimens from their habitat. This is not only due to their very limited occurrence in a very small area, but also to the fact that the frogs probably spend most of their time high up in the trees, where humans cannot reach them. Other tree-dwelling frogs at least come within sight for spawning, but the fringe-limbed treefrogs save themselves the hassle of climbing down to the forest floor and have discovered a very special nursery for themselves: tree hollows, which are often filled with water in the humid cloud forest climate. A one-room attic flat with its own bathroom, so to speak. This is where the frogs raise their offspring. Very convenient.

And that’s not all that’s unusual about them: because good tree hollows are rare, male frogs defend theirs fiercely against rivals and have even developed a kind of stabbing weapon for this purpose, a thorn-like structure on the ‘thumb’ of their front feet, which they use to engage in bitter gladiatorial combat. The frogs’ rather scrawny and fringed appearance, which gives them their name, serves as camouflage on trees because it blends in so well with the bark. And the large webbing between their toes can be used to steer or slow down their gliding flight through the air when jumping from branch to branch or even from tree to tree, like a kite.

Quite a lot of peculiarities for a single frog. It is perfectly adapted to life in the cloud forests on the slopes of its volcano. But only there. There, it finds itself at a disadvantage, webbed feet or not, as its already tiny habitat is being increasingly deforested. In addition, there is the threat of a fungal disease that has been introduced. As a result, the Lichenose Fringe-limbed Treefrog seems virtually extinct, even though it has hardly ever been seen. Almost everything we know about it comes from observations in terrariums, because some of the frogs have come into human care. Fortunately, they have produced offspring and demonstrated their unusual reproductive strategy. Today, these offspring may be the last chance to preserve this extraordinary species for the future – even if the tree frogs in their native habitat are struggling to survive.