Scorpions go terminator mode and reinforce their weapons with metal - Ars Technica

Scorpions are armed with dual front pincers (technically known as chelae or pedipalp appendages) and a venom-injecting telson, or stinger, on the posterior of their tail. These things look dangerous enough on their own, but a chemical examination showed they contain metals like zinc, manganese, and iron.

“That the metals are there has been known since the 1990s,” said Sam Campbell, a biologist at the University of Queensland, Australia. “What we didn’t know was whether scorpions evolved to be like that or if it was accidental and they were just picking the metals up from the environment.”

To answer this question, Campbell and his colleagues examined how metals are distributed across the stingers and pincers of different scorpion species. Based on their data, detailed in a recent study published in the Journal of The Royal Society Interface, there was nothing accidental about it.

Campbell’s team focused on 18 scorpion taxa selected from a large collection at the Smithsonian National Museum of Natural History. To map the molecular structure of the scorpions’ weaponry, the researchers used high-resolution scanning electron microscopy coupled with micro-X-ray fluorescence imaging. These methods allowed them to build color-coded maps of all the stingers and pincers, with individual metals localized in extremely high detail. Based on these maps, the team could reconstruct metal enrichment patterns within the weapons.

In most of the studied specimens, zinc was highly concentrated at the extreme tip of the aculeus, the needle-like envenoming structure. “Zinc has all to do with hardness and ensuring that we retain the strength of the tip of the stinger,” Campbell explained. Just below this zinc-fortified tip, manganese often became the dominant metal in a distinct region lower in the aculeus.

The purpose of manganese in the region below the aculeus, the team speculates, is probably to improve the flexibility and absorption of vibrations. Having both metals arranged in this way turns the stinger into a biological spear capable of punching through tough hides or exoskeletons of prey. “It makes sense because a scorpion’s sting is quite aggressive and produces quite a lot of force, so the stinger has to take it without snapping,” Campbell said.

The team noticed a similarly clever metal arrangement in the pincers. Zinc and iron enrichment was present only in the granular rows of the chela, specifically in the jagged, tooth-like bumps called denticles on the movable outer segment. The layout resembled a samurai sword, where the hardest material is concentrated mainly along the cutting edge. “When these denticles, these teeth pop up, we see the enrichment and then, in the entire area around them, all the rest of the claw, there is no metal whatsoever,” Campbell said.

But when Campbell and his colleagues took a deeper dive into species-to-species variations in the scorpions’ weaponry design, they encountered yet another layer of complexity. “One of the things that made me want to do this investigation is that scorpions are all very different,” Campbell said. “They have different sizes and shapes of their pincers and their stingers, and there are significant differences in their behavior.”

The team wanted to learn whether these differences are reflected in scorpions’ patterns of metal enrichment in their weaponry. It turned out they are.

Scorpion species use their pincers and stingers in different ways. Species in the Buthidae family use their stingers for hunting prey and usually have long and slender pincers with relatively weak crushing power. On the other hand, adults of the Pandinus imperator species, known as the Emperor Scorpion, use the stingers only for self-defense and rely on their robust, massive claws to subdue and crush insects, young mice, and small lizards they feed on.

Going into the study, the team hypothesized that pincers built for generating high crushing force would contain the highest levels of metal to provide maximum hardness, while enrichment in the weaker, slender pincers would be lower. While this held true for zinc, the correlation was the exact opposite for iron.