Scorpions Really Are Metal. Their Stingers and Claws Are Reinforced With Actual Metal

Zinc, iron, and manganese help scorpions sharpen different tools for different lives.

by · ZME Science

A scorpion does not look like an animal in need of more firepower. It arrives already armed, with claws at one end and a hypodermic tail at the other. But under a microscope, its weapons turn out to be even stranger than they look. They are not just chitin and venom. They are laced with metal.

In a new study, researchers examined the claws and stingers of 18 scorpion species and found that the animals enrich their weapons with zinc, iron, and manganese in strikingly different ways. These metals do not simply make every sharp part harder. Instead, scorpions appear to place different metals in different weaponized body parts depending on how they hunt, grip, sting, and survive.

Scorpions, it seems, have spent hundreds of millions of years solving a problem engineers know well: how to reinforce the parts most likely to fail.

A hidden scorpion metallurgy

To see what scorpions were hiding in their claws and stingers, Sam Campbell of the University of Queensland and his colleagues went to the Smithsonian National Museum of Natural History. There, in the museum’s collections, they found preserved scorpions representing a broad sweep of the scorpion family tree.

The researchers removed the animals’ stingers and claws, then studied them with scanning electron microscopes and X-ray techniques. The result was a set of chemical maps in which the weapons lit up in different colors: zinc at the tips of many stingers, manganese farther down, and zinc or zinc-and-iron along the biting edges of claws.

“The microscopic-scale methods we used allowed us to identify individual transition metals in extremely high detail, showing us how nature skillfully engineered these metals in the scorpion’s weapons,” said Edward Vicenzi, a research scientist at the Smithsonian Museum Conservation Institute.

SE micrograph of the entire telson (stinger) of the Tanzanian red bark scorpion (Babycurus Jacksoni). Image includes the telson vesicle, in which the two venom producing glands can be found. Muscles surrounding the glands will contract internally, pushing venom up through conduits to the tip of the telson (termed the aculeus). This species also features a subaculear tubercle (small protrusion above the stinger) with an unknown function. Credit: Sam Campbell/University of Queensland.

The metals were not spread evenly. In the stinger, known as the telson, the enrichment clustered in the aculeus, the curved needle that pierces prey. In many species, zinc sat at the extreme tip. Manganese often took over farther down. A sharp boundary separated the metal-rich part from the rest of the tail, including the venom bulb.

In the claws, the pattern changed. The metals concentrated in the denticles, the tooth-like structures along the cutting edge. In some species, the claw teeth carried zinc alone. In others, zinc and iron reinforced the same edge.

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The metal distribution makes sense because these are the places that take punishment. A scorpion can replace its exoskeleton when it molts, but only up to a point. Once it reaches adulthood, a broken stinger or cracked claw may become a lifelong injury and disability.

Choose your weapon

Micro X-ray fluorescence microscopy of the metals present the stinger of an emporer scorpion (Pandinus imperator). Zinc (red) is concentrated towards the tip, and manganese (green) is concentrated farther down, with a clear line in between. Credit: E.P. Vicenzi/Smithsonian Museum Conservation Institute and NIST.

Scorpions share a body plan, but they do not all live by the same strategy. Some are crushers. Others are stabbers.

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Large-clawed species often seize prey and overpower it with their pincers, saving their sting for defense or for especially difficult prey. Species with slender claws and more prominent tails often use the pincers as restraints while the stinger delivers venom.

The study found a clear trade-off. Species with more zinc in their claws tended to have less zinc in their stingers, and species with zinc-rich stingers tended to have less in the claws. The researchers tested this pattern while taking shared ancestry into account, so they were not just comparing unrelated animals as if evolution had started from scratch each time.

The pattern suggests that scorpions do not reinforce everything equally. They invest in the weapon that matters most, and what matters most can be different across scorpion species.

The surprise was in the weak claws

Rough thicktail scorpion (Parabuthus raudus). Paratuthus scorpions’ venom is quick-acting, so they do not need to rely as much on their pincers to capture prey. Credit: Peter Webb.

At first, the researchers expected the biggest, strongest claws to carry the most metal. That would seem obvious. If a claw works like a crusher, surely it needs reinforcement.

But the data ran the other way. The highest zinc enrichment appeared in more slender claws, which produce weaker crushing forces.

“This points to a role for zinc beyond hardness, perhaps playing a bigger role in durability,” Campbell said.

Secondary electron micrograph showing the claw (top down) of an Australian scorpion.  Credit: Sam Campbell / University of Queensland

That makes sense when the claw’s job changes. A slender claw may not crush prey outright. Instead, it must hold a struggling insect long enough for the stinger to strike. That kind of work demands grip, wear resistance, and endurance under repeated stress.

Yael Politi, a biomaterials scientist at the Dresden University of Technology who was not involved in the study, told Science that the incorporation of metal ions likely compensates for structural fragility. Rather than acting only like armor, zinc may help a delicate weapon endure.

Spider fangs, ant mandibles, bee stingers, wasp stingers, and centipede forcipules can all contain metals. In these animals, evolution has repeatedly found ways to make lightweight biological materials sharper, tougher, or more resistant to wear.

“Taking this metal distribution and placing it in an evolutionary context [is] superexciting,” Politi told Science.

A clue from ancient predators

Peninsular Burrowing Scorpion (Opistophthalmus latro). The burrowing scorpions use their large and durable pedipalps (pincers) to dig burrows. They are less venemous than fattail scorpions and rely more on their large pinchers to crush prey. Credit: Paul Bester.

Scorpions are among the great survivors of animal evolution. Their lineage stretches back more than 400 million years, and their basic form has remained recognizable for an astonishing span of time. That does not mean they stopped evolving. Instead, much of their innovation may have taken place at smaller scales, in things such as venom chemistry, behavior, and the microscopic structure of their claws and stingers.

The study also raises new questions. Do scorpions get these metals from their prey? Do soil chemistry and habitat affect how much metal they can build into their exoskeletons? Do females and males differ? Do young scorpions enrich their weapons in the same way adults do?

Campbell told Gizmodo that the study tested 18 species, but “There are close to 3,000 species of scorpion, and they all likely feature metal enrichment!”

For now, the work offers a new way to look at an old predator.

The findings appeared in the Journal of the Royal Society Interface.