Slow worms, like many other lizards, have a tail that can be broken as part of their defensive mechanism (an escape strategy). The scientific term for this phenomenon is ‘autotomy’ (auto meaning self, tomos meaning cut) and is the self-induced releasing of a specific body part. One of their tail vertebrae is actually broken in half. Its tail separates at a ‘fracture plane’, one of many fracture planes that are regularly spaced along the length of the tail, either in between vertebrae or in the middle of each vertebrae.
It doesn’t end there – the predator’s attention is directed to the tail ‘twitching’ back and forth, as the lizard remains still or slowly repositions itself so as to launch itself away from the predator. The negative side to this is that tail loss is costly. No slow worm wants to lose its tail unless its life is seriously in danger. Losing a tail represents a loss of fat and protein, both stored in the tail and that which is dedicated towards the regrowth of a new tail. Losing a tail when young actually puts a young slow worm at a higher risk of being preyed upon again shortly afterwards. The tail eventually regrows, but is cartilaginous as opposed to
skeletal. While autotomy is costly in terms of the overall loss to the lizard, it is apparently quite effective as a survival strategy, as this defence strategy is fairly widespread through the lizard families. Incidentally, of course, the ‘fragilis’ in the latin name for the slow worm ‘anguis fragilis’ refers to the fragile nature of its tail.