A Dusky Toadlet displaying patches normally concealed

The underside of a Yellow-bellied toad

The unkenreflex is a passive defense posture adopted by toads, frogs and salamanders. When threatened by predators, they twist their bodies, or arch their backs and limbs to expose brightly-colored aposematic skin. The normally-concealed red, yellow, white and black patterns on the underbelly, inner surfaces of the limbs or underside of the tail serve as a visual warning to predators. To reinforce the warning, unkenreflex is sometimes accompanied by toxic and malodorous secretions from glands in the skin. This is the case with the Rough-skinned Newt, who releases the toxin tetrodotoxin while engaging in the unkenreflex.¹

This behaviour is named after the Fire-bellied toad (German: Unke, plural: Unken) which exhibits this reflex. The same behaviour may be observed in other amphibians that do not have any warning colours.²

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