In Cameroon, some frogs are nothing like the benign variety we’re used to. If you’re a predator, you sure don’t want to mess with Trichobatrachus robustus — a hairy frog species that, when cornered, will go as far as breaking its own bones to unleash a hidden ace up its sleeve. Puncturing right through its toes are sharp claws which the frogs use as a last line of defense. T. robustus can be quite dangerous, which is why Cameroonian hunters use  long spears and machetes to kill the frogs for food, to avoid being cut.

Credit: Flickr user TNS Sofres // Wikimedia Creative commons.

Credit: Flickr user TNS Sofres // Wikimedia Creative commons.

Males of T. robustus, also known as the horror frog or Wolverine frog, have hair-like structures on the body and thighs which appear in the breeding season. The ‘hairs’ are in fact dermal papillae which contain numerous blood vessels that are thought to function a bit like external gills. These structures help the frogs intake more oxygen through their skin while they take care of their brood.

The claw breaks away from a small piece of bone (see arrow) at the tip of the frog’s toe

The claw breaks away from a small piece of bone (see arrow) at the tip of the frog’s toe. Credit: Harvard University Museum of Comparative Zoology

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The most interesting feature are the claws found in the hind feet only, nestled inside a mass of connective tissue. These claws, which are entirely made of bone and not collagen, are connected at one end to a muscle. When the animal is attacked, it contracts this muscle pulling the claw downward. The sharp end breaks away from the bony tip, cutting right through the toe pad and emerging on the underside. David Wake, at the University of California, Berkeley, says this approach to defense/weaponry appears to be unique in the animal kingdom.

The short, but sharp claws of the frog. Credit: Harvard University Museum of Comparative Zoology

The short, but sharp claws of the frog. Credit: Harvard University Museum of Comparative Zoology

No one has ever seen a horror frog retract its claws, and since there are no muscles that could put them back inside researchers think these are non retractable. Once out, they stay out. But this isn’t a certainty, since amphibians can be quite surprising. Generally, amphibians heal fairly quickly so tissue might be restored.

T. robustus has seen its numbers fall pretty substantially over recent years, owing mostly to deforestation and habitat loss. The species isn’t considered endangered yet, though. These animals are also hunted by the Bakossi people who traditionally believe that the frogs fall from the sky and, when eaten, help childless human couples become fertile.