Back in March I was contacted to say a mass mortality event had been seen, with hundreds of dead toads found at a loch on the Isle of Islay. The toads showed horrific injuries, their back legs turning white and beginning to break down. The symptoms were exactly the same in all the victims, with wasting always starting from the hind leg toes and working up to the midriff (see picture). What was discovered on closer inspection was that these toads were actually often still alive, even when wasting was very far progressed. Both the toads on the picture are still alive. Nothing like this had ever been observed at this loch before.

I had never heard of a disease that caused such symptoms and sent the details to a number of amphibian experts across the UK. Nobody had an idea what could be causing it. I was kindly sent a specimen, which I forwarded to disease experts at the Institute of Zoology for post mortem.

Katie Colville sent this explanation in return:
Both hind limbs had been completely ‘degloved’ – the muscle and bone of each limb had been ‘extracted’ leaving only the skin ‘shell’ of each hind limb in place. There was an associated ‘cut’ across the back of the abdomen at the level of the pelvis. It’s thought that these kind of lesions are the result of otter predation. It’s thought that otters deglove the legs in order to avoid the noxious glands in the skin.

So the mystery is solved, a very clever behavioural adaptation of otters to avoid the toxins in toad skin. Many thanks to Justin Ruthven-Tyers for such an interesting case. It will be very interesting to see how the toads fare next year.

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