Episode 479: Metal Animals

Further reading: Beavers Have Metal Teeth Show transcript: Welcome to Strange Animals Podcast. I’m your host, Kate Shaw. Let’s find out about some animals that incorporate metal into their bodies in more than just trace amounts. We’ll start with the scaly-foot gastropod, a deep-sea snail. It lives around hydrothermal vents in the Indian Ocean, about 1 and ¾ miles below the surface, or about 2800 meters. The water around these vents, referred to as black smokers, can be more than 350 degrees Celsius. That’s 660 degrees F, if you even need to know that that’s too hot to live. The scaly-foot gastropod was discovered in 2001 but not formally described until 2015. The color of its shell varies from almost black to golden, depending on which population it’s from, and it grows to almost 2 inches long, or nearly 5 cm. It doesn’t have eyes, and while it does have a small mouth, it doesn’t use it for eating. Instead, the snail contains symbiotic bacteria in a gland in its esophagus. The bacteria convert toxic hydrogen sulfide from the water around the hydrothermal vents into energy the snail uses to live. It’s a process called chemosynthesis. In return, the bacteria get a safe place to live. The snail’s shell contains an outer layer made of iron sulfides. Not only that, the bottom of the snail’s foot is covered with sclerites, or spiky scales, that are also mineralized with iron sulfides. While the snail can’t pull itself entirely into its shell, if something attacks it, the bottom of its foot is heavily armored and its shell is similarly tough. Researchers are studying the scaly-foot gastropod’s shell to possibly make a similar composite material for protective gear and other items. The inner layer of the shell is made of a type of calcium carbonate, common in mollusk shells and some corals. The middle layer of the shell is regular snail shell material, organic periostracum, which helps dissipate heat as well as pressure from squeezing attacks, like from crab claws. And the outer layer, of course, is iron sulfides like pyrite and greigite. Oh, and since greigite is magnetic, the snails stick to magnets. The scaly-foot gastropod is the only animal known that incorporates iron sulfide into its skeleton, but other animals use metals in their teeth. Some spiders have tiny amounts of zinc in the tips of their fangs. Some mollusks have small amounts of iron in the teeth of their radulas—you know, the tongue-like structure used to scrape food off rocks. The teeth of the limpet, a type of mollusk, may be one of the strongest structures in the world. It contains goethite nanofibers, and goethite is a type of iron. The teeth of beavers and some other rodents contain iron in the enamel coating. This makes the teeth much harder, although the amount of iron is quite small and unstructured. Most other mammals, including humans, have magnesium in tooth enamel instead of iron. The iron content makes the teeth look orange because of rust. Bloodworms are disgusting horrible worms that my uncle used to fish with when we visited the beach when I was a kid. I was scared of the bloodworms, which irritated my uncle, because I was very vocal about hating the worms and he wasn’t catching any fish with them. Bloodworms live in the sand or silt of shallow water, usually in the ocean but since they can tolerate low salt levels, they may also live farther inland in canals and inlets. Some species can grow nearly 15 inches long, or 37 cm. They’re usually pink or reddish in color with bristles along the body and four little antennae on the head. But the reason I’m talking about them here is that their teeth are reinforced with copper that makes them nearly as hard as teeth coated with enamel. Its jaw also contains copper ions. Copper is toxic to most animals, which may be the source of the bloodworm’s venom. That’s right: horrible worms are also venomous. Another invertebrate that incorporates metal in its body is the parasitic fig wasp. Fig wasps are interesting and there are a lot of them. Figs are pollinated by fig wasps that are not parasitic. T