Scorpions reinforce their claws and stingers with metals

Scorpions reinforce their claws and stingers with metal, turning these weapons into the equivalent of a steel-capped boot.

The use of metals to strengthen vulnerable parts of the body, such as the teeth of vertebrates like Komodo dragons (Varanus komodoensis) – is already known, and the areas of a scorpion that contain metals are visible as spots to the naked eye.

Sam Campbell of the University of Queensland, Australia, and colleagues examined the claws and stingers of 18 scorpion species from around the world to determine the extent and composition of their metallic reinforcements.

The team used two different X-ray techniques and electron microscopy to examine the scorpions, which allowed them to map the presence of three main metals: iron, zinc and manganese. They also found traces of various other elements, including copper, nickel, silicon, chlorine, titanium and bromine.

The metals are found largely at the tips of the stingers and along the cutting edge of the claws, as well as in their mouths, teeth and tarsal claws, making their weapons “like a steel-toed boot,” Campbell says. The rest of the animal’s exoskeleton is still hard, but much softer in comparison.

Scorpions all fluoresce light green or blue under ultraviolet light. But body parts enriched with metals don’t glow when exposed to UV, the team found.

It is not yet known how scorpions obtain the metals they incorporate into their exoskeletons, although their prey is the most likely source.

The team also found that different species of scorpions contained more metal in different parts of their bodies, which is linked to their behavior. “What we identified was that when zinc was high in the claws, it was low in the stinger, and vice versa,” says Campbell. “Since scorpions use their weapons so differently, it is possible that metal enrichment has adapted to provide beneficial biomechanical properties to weapons where the scorpion needs them most.”

Metal enrichment in animal tissues appears to be more common than previously thought, says Aaron LeBlanc of King’s College London. “A growing number of studies also highlight this phenomenon in the case of vertebrate teeth,” he says. “The next logical step after discovering these traits is to try to understand how they evolved across major lineages, and this study is pioneering for that reason.”