Coming in 2 different types, ‘spearers’ and ‘smashers’, Mantis Shrimps use their highly specialised raptorial appendages to either eviscerate or bludgeon their unfortunate prey.
But up until now, just how ‘smasher’ Mantids manage to maintain the condition of their clubs has been a mystery. The fact that they manage this at all is even more amazing when you consider that the force exerted by each blow can exceed 700 Newtons, with the club accelerating at over 10,000 gs up to 23 metres per second before impact (actually it moves so fast that imploding cavitation bubbles are also produced).
Researching the mechanism, David Kisailus at the University of California, Riverside, and his colleagues found that the head of the club is divided into three main layers. The outer layer is mostly made of a tough mineral called Hydroxyapatite (also found in teeth and bone) which is arranged in neat crystals, making for a strong coating. Beneath a less ‘organised’ second layer of Hydroxyapatite there is a layer of Chitin composite (a polymer that crustaceans use to make their shells, mixed with Calcium carbonate).
The secret of the structures resilience lies in the difference in the flexibility of each layer. This layering makes it hard for fractures to propagate from one layer to the next. Furthermore, the Chitin layer is arranged in spirals which means that any cracks in that layer tend to follow spiral patterns, which don’t weaken the overall structure.