Horror Frog (Hairy Frog + Otton Frog) — Breaks Its Own Bones To Create Claws

February 8, 2015 in Animals & Insects

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The Horror Frog — a frog that breaks its own bones to make claws — perhaps you’ve heard of such an animal and questioned whether it’s actually real? After all what kind of animal would intentionally break its own bones?

Well, I’m here to tell you that it is real — and there are actually at least two species of frog that do, in fact, break their own bones intentionally to make claws that they then use in fighting. Making both species — the Hairy Frog of Central Africa, and the Otton Frog of southern Japan (Ryukyu Islands) — clearly deserving of the (somewhat humorous) moniker “the Horror Frog”.

Horror frog claw Otton

This article will provide information on (and of course pictures of) both species — the hairy frog (Trichobatrachus robustus); and the Otton frog (Babina subaspera). Enjoy.

The Otton Frog — Also Known As The Horror Frog

Otton frog

The Otton frog (Babina subaspera) is a type of frog classified as being in the family Ranidae — that breaks its own bones in order to make claws… The species is often referred to as the horror frog, and is native to the islands of Amami Ōshima + Kakeromajima in the Ryukyu Islands, Japan.

While the species was once common enough to be considered a source of food, population numbers have fallen in recent years — mostly as a result of deforestation, and habitat loss. The introduction of the mongoose to the islands has also played a part though.

The species is found mostly in subtropical + tropical moist lowland forests, freshwater marshes, and intermittent freshwater marshes.

Research has shown that while both males and females possess the false spike thumbs, only the males appear to use them — mostly for fighting, but also mating (holding onto the females).

“Why these ‘fifth fingers’ exist in some species remains an evolutionary mystery, but the extra digit of the Otton (horror frog) is in fact a pseudo-thumb,” explained Dr Noriko Iwai, of the University of Tokyo, while commenting on earlier research. “The digit encases a sharp spine which can project out of the skin, which fieldwork demonstrates is used for combat and mating.”

Horror Otton frog claws bones

“While the pseudo-thumb may have evolved for mating, it is clear that they’re now used for combat,” she continued. “The males demonstrated a jabbing response with the thumb when they were picked up, and the many scars on the male spines provided evidence of fighting.”

Which isn’t surprising as the environment of the Amami Islands is a very competitive one for frogs — one where the male Otton frogs regularly fight over the “best” places to construct nests, sometimes to the death.

“More research is needed to look at how the pseudo-thumb evolved and how it came to be used for fighting,” Dr Iwai noted. “The thumbs use as a weapon, and the danger of the frogs harming themselves with it, makes the Otton pseudo-thumb an intriguing contribution to the study of hand morphology.”

As stated before, there are growing threats to the continued survival of the horror frog though — in particular, the aforementioned high rates of deforestation and habitat loss seen in the region in recent years. It would be unfortunate to see such a strange animal as “the horror frog” go extinct simply so people can continue buying cheap mass produced furniture at IKEA (or somewhere else) wouldn’t it?

The Hairy Frog — Alternately Known As The Horror Frog, The Spiked Frog, or The Wolverine Frog

Hairy frog

The hairy frog (Trichobatrachus robustus), is a species of frog that’s classified as being in the Arthroleptidae family of frogs that’s native to the forests and jungles of Central Africa. The species is occasionally referred to as the horror frog, the spiked frog, or the wolverine frog. It’s monotypic within the genus Trichobatrachus.

The common name (hairy frog) refers to the rather hair-like structures that cover the bodies and thighs of adult males.

Adult hair frogs typically measure a bit under a half-foot in length once fully grown. The skull of the species is fairly broad, and features a short rounded-snout. Males are a good deal bigger than females — and possess a large vocal sac for vocalizations, and black spines lining its first manual “fingers”, as well.

With regard to the “hair” running down the legs of the breeding age males, these are actually “dermal papillae” — and contain numerous blood vessels that are thought to function a bit like external gills. It’s presumed that the reason for this is to aid the males when they are guarding their eggs after the female lays them and leaves. Like with many species of frog, it’s the male hairy frogs that “guard/raise” the young/eggs.

So, in other words, the horror frog is apparently more a protective father, rather than a creature out of a horror movie. Lmao.

Hairy frogs are largely terrestrial, but the breeding process occurs in water — where eggs are generally laid onto rocks in streams.

The tadpoles of the species are actually fairly aggressive, and are carnivorous — with multiple rows of “horned” teeth.

The adults feed mostly on insects, spiders, slugs, and other small animals

With regard to the qualities that earned the hairy frog the title of “horror frog” — the species actually possesses retractable “claws” which are projected through the skin when he frog is threatened. The catch though, is that these claws are actually the frog’s bones… That it breaks and forces through its skin… Intentionally…

Not quite like anything you’ve heard of before huh? Except maybe in popular entertainment I suppose.

The researchers found a small bony nodule nestled in the tissue just beyond the frog’s fingertip. When sheathed, each claw is anchored to the nodule with tough strands of collagen, but, as discovered firsthand, when the frog is grabbed or attacked, the frog breaks the nodule connection and forces its sharpened bones through the skin.

It’s not currently known how exactly the claws are retracted, but it seems to happen fairly rapidly — over just a couple of days (or less). The process seems to be passive, and occurs perhaps as a part of the healing process of the damaged soft-tissue.

As noted by the leading amphibian researcher and biologist, David Wake, at the University of California – Berkeley, this approach to defense/weaponry appears to be unique in the animal kingdom. (Though the Otton frog possesses something that is in many ways very similar.)

While T. robustus has seen its numbers fall pretty substantially over recent years, owing mostly to deforestation and habitat loss, the species isn’t currently considered to be endangered, or anywhere near extinct.

References: University

Image Credits: N. Iwai; Public Domain

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