Different strategies towards strength: Unveiling the role of Zn vs Mn/Ca and chitin arrangement in scorpion stingers

Arthropods and especially scorpions often use metal ions to harden their cuticle. In this study we analyse the chitin fibre arrangement, metal content and distribution and mechanical properties of the stingers of two scorpions: the buthid scorpion Centruroides platnicki (PS) and the diplocentrid scorpion Nebo whitei (NS). Results show that both scorpions incorporate the same elements, Zn, Mn and Ca, but in different locations in the stinger cuticle. While NS uses Zn ions as hardening agent in the epicuticle, PS uses Mn/Ca ions. Interestingly, Zn ions were also found in PS but had no impact on the enhancement of the mechanical properties of the stinger. The use of different metal ions in biological materials is likely to enable precise adjustments of material properties to suit not only mechanical but biological functions as well.