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"It's about fifty or sixty feet high, and it only eats metal."
Hogarth Hughes, The Iron Giant
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One of the easiest ways to portray an organism as different from humans is to give it radically different dietary needs. And one of the easiest ways to do that is to have the organism consume metal. Now, while in real life humans and other carbon-based organisms need to consume trace amounts of metals to stay healthy (for example, the iron found in green vegetables is necessary for the production of metalloproteins like hemoglobin), this trope is about creatures that consume pure, refined metal for food. So a person eating the aforementioned green vegetables would not be an example, but a monster eating a steel sword would be.

Such metal-eating creatures often present a unique threat to many of the constituent parts of human civilization compared to other entities with strange diets. After all, automobiles, I-beams, electrical wires, and computers all need metal to manufacture, so a monster that devours such objects can throw people's lives into disarray even if the people themselves are unharmed. Heroes can also find it difficult to fight monsters that are able to eat their weapons and armor. At other times, however, metal-eating organisms can be beneficial to humans, such as by recycling/refining the metals through digesting and expelling them. There's also an occasional overlap with Nuclear Nasty; radioactive elements such as uranium and plutonium are metals, and irradiated monsters are likely to seek out such substances for a meal.

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It is common for the metal eaters to be creatures predominantly made of metal themselves, usually with some kind of Sculpted Physique. It is also a common trait among robots, in lieu of them needing just electricity and factory-made replacement parts like in real life. A meal for these characters may consist of Palette-Swapped Alien Food with a metallic color and texture, oftentimes with visible seams and rivets to emphasize that it is made from metal. And sometimes, the eater is actually a human or humanlike character who chows down on metal in order to be more "macho".

Subtrope to Bizarre Taste in Food. Sometimes an example of Extreme Omnivore, unless the character only eats metal. Extreme Omni Goats are very frequently shown eating metal; tin cans, in particular, are a staple item in their diets. Metal is also a common food for Grey Goo. Compare with Eat Dirt, Cheap, which also deals with characters eating a substance that comes from the ground. Not to be confused with Tasty Gold, unless the characters really do eat the gold outright.

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Examples:

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    Anime & Manga 
  • In Dragon Ball GT, Pan's Robot Buddy, Giru, eats metal and anything made of metal, including the Dragon Radar.
  • Eat-Man: the protagonist Bolt Crank has the ability to eat anything and then manifest the consumed objects from his body at will. He especially likes metal, and is often shown snacking on bolts and screws.
  • In Fairy Tail: Dragon Slayers can, in addition to normal food, consume the element that makes up their magic to quickly restore their magical power and sometimes as a substitute for normal meals. This trope thus comes into play for Gajeel, the Iron Dragon Slayer, who is often seen eating from a bowl of nuts and bolts during his downtime.
  • In the Pokémon Sun and Moon anime, Ash's Meltan eats metal.
  • In One Piece Wapol is capable of eating metal (among other things..) and even merging with it courtesy of the Baku-Baku no Mi/Munch-Munch Fruit.
  • Casshern Sins features numerous examples of what would best be described as Robo-cannibalism. The only people still alive are all robots in various forms who all fear the inevitability of death as their metal bodies eventually break down and rust away. Casshern himself is seemingly immortal, and is subject to numerous people who desperately want to eat him in hopes of gaining that immortality. Throughout the series are are many rumors of similar robots who claim to be immortal, and at some point or another meet their end and are ravenously devoured by the hopeless masses.

    Comic Books 

    Comic Strip 
  • Redeye: There's a goat that feeds exclusively on metal, preferably tin cans.

    Fanfiction 

    Film — Animated 
  • In Despicable Me 2, El Macho demonstrates the barbarian power of his new genetically-modified Minions by feeding one an assortment of dangerous metal items, from a chainsaw to a police car to a nuclear bomb.
  • The eponymous character of The Iron Giant is an extraterrestrial robot who starts off eating metal objects like TV antennas and the support structures of a power plant. When he starts hiding out at Dean's scrapyard, he eats the old cars and other junk there — though he also eats some of Dean's abstract art pieces that he wasn't supposed to eat.
  • In Shark Tale, the Great White Sharks are all shown to be Extreme Omnivores with part of their diet being metallic items, and since Lenny is a 'vegetarian shark' that's pretty much all he eats. There is some Truth in Television to this as while sharks don't actually need to consume them, such objects do have a tendency of ending up in their stomach.

    Film — Live-Action 
  • The eponymous character of Pulgasari is a metal-eating monster brought to life from an old blacksmith's clay figurine. As he eats more and more, he grows into a giant Kaiju who helps the peasants revolt against the evil king who had been confiscating their farming and cooking tools to reforge them into weapons. But even after the king is vanquished, Pulgasari is still hungry, forcing the peasants to feed their tools to him instead.

    Franchise 

    Literature 
  • Age of Fire: The dragons' metal diet is what makes their scales so strong, and failure to include a steady amount of metal in one's diet is equivalent to vitamin deficiencies. In fact, AuRon is special for averting this, as he is a rare scaleless dragon and so doesn't need to eat any, allowing him to live far from the hominids who mine the stuff.
  • Book of Imaginary Beings: One variant of the Alicanto bird feeds on gold, while the other feeds on silver. This heavy diet has the side-effect of making it incapable of flight, and it cannot even run with a full belly.
  • In Evgeny Filenko's Galactic Consul series, the title character once gets stranded on an alien planet after an indigenous creature (that appears like thick fog) consumes every metal component of his gear, including his communication device.
  • The Heroes of Olympus: Arion is an immortal horse that only eats gold.

    Live-Action TV 
  • In the Farscape episode "Liars, Guns And Money Part 2," the Living Ship Moya ends up suffering an infestation of metal-eating parasites; from what little we see of their feeding habits, they project digestive enzymes onto metal walls and floors, then drink the results. Worse still, these "metalites" arrived on board via the bank container the crew stole in the previous episode and are perfectly disguised as valuable ingots, so nobody recognizes the source of the problem until it's almost too late to save Moya. In the end, the crew are forced to burn the afflicted areas, saving Moya from the parasites but leaving her badly wounded.
  • Monster Warriors: In "Attack of the Junk Monster", the Monster of the Week is a giant metal-eating radioactive junk monster: one of Klaus' seemingly failed experiments, but when he threw it out it started absorbing all the metal in the junkyard, becoming a radioactive menace so deadly even Klaus wanted to destroy it.
  • Star Trek: The Next Generation episode "Cost of Living". Nitrium is a metal alloy commonly used in Federation starship technology, including the computers, warp drive and life support. The Enterprise is invaded by a parasite that eats nitrium, causing ship systems to fail and endangering the crew.
  • Ultra Series:
    • In the original Ultraman, a Monster of the Week named Goldon eats pretty much what the name suggests it does. In fact, Goldon's body is partially made of gold!
    • Pagos from Ultra Q feeds on uranium, giving it atomic abilities. This is also the case with a similar monster named Gabora that appears in Ultraman and Kingsaurus III from Return of Ultraman.
    • The Arindo Ants of Ultraman Taro eat steel and concrete like termites eat through wood, causing structures to collapse.

    Tabletop Games 
  • Dungeons & Dragons:
    • The aurumvorax is an eight-legged wolverine-like animal that eats metals and ores, but has a special affinity for gold.
    • Rust monsters subsist on rust, which they can create by touching any kind of metal. Their cousins, the folugubs, can liquefy crystals at a touch and feed on the result. They corrode metal extremely quickly, enough so that corroding and consuming enemy weapons mid-combat is a very viable combat tactic for them. Planescape reveals via retcon that rust monsters are larval forms of a much more dangerous creature called a rust dragon, which is encountered on Acheron. Their breath weapon can rust and corrode an arsenal's worth of armor in one blast. Fortunately, Acheron is full of scrap metal, but rust dragons crave metal from outside sources the way humans enjoy candy. (A rust dragon who finds itself in Mechanus, a plane made entirely out of gigantic metal gears, is a planar bull in a china shop, and is quickly hunted down by the inhabitants.)
    • AD&D 1st Edition Fiend Folio: The khargra is a monster from the Elemental Plane of Earth. It normally "swims" through solid rock looking for metal ores to consume. If it encounters creatures with metal items (e.g. armor and weapons), it will leap out of the surrounding rock and bite the items in an attempt to eat them.
    • AD&D 2nd Edition Monstrous Manual: Xarens are stony Elemental Embodiments whose primary diet is metals, unlike their close relatives the Xorn, who prefer unrefined minerals and gems. They're not hostile, but, unfortunately for adventurers, enchanted metals like magical weapons and armour are especially delicious to them.
    • 1st Edition AD&D Monster Manual. The Xorn is a creature from the Elemental Plane of Earth that can smell metals up to 20 feet away. If it encounters Player Characters who are carrying metal (copper, silver, gold and so on), it will demand that they hand over the metal(s) so it can eat them. It will try to take the metals by force if the characters refuse.
    • Dragon magazine #53 "Dragon's Bestiary". The creature known as the argas can improve its armor class by eating certain metals. Iron, mithril and adamantite improve armor class to AC 2, -1 and -3, respectively. Eating silver or gold improves armor class by one or two points, respectively. An argas can receive the benefit from each metal only once, so the best armor class one can have is -6 (after eating adamantite, silver and gold).
  • Exalted: Furnace rhinos were created by the Primordial Autochthon to be living refineries for useful metals, and fulfill their purpose by consuming ores and scrap metal, purifying them internally and depositing the resulting materials in their bodies — regular metals make up their hide, while the magical materials form their horns.
  • Traveller, Journal Of The Travellers Aid Society #15, article "The Bestiary". Doyle's Eel is a Silicon-Based Life form that eats metal. If it infiltrates a starship it will try to eat metals, silicon and some plastics, which can cause serious damage. It will also try to lay eggs and hatch out more of them, which will cause even more damage.

    Toys 
  • Flick-to-Stick Bungees: The second series, Bionic Bungees, has a character named Kitor who is stated in his bio to gluttonously consume metal without considering if other Bungees will need it.

    Video Games 
  • Deep Rock Galactic: The reason why loot bugs erupt into showers of Gold and Nitra upon dying is that they eat them. If you leave your resources unguarded near a lootbug, it will waddle over and eventually eat the raw ore on the floor. Unfortunately for you, you don't get the ore they eat back if you kill them.
  • Kantai Collection: By the nature of things, characters are usually depicted as straight-out eating bauxite, which is one of the resources in the game. Especially Akagi, who is depicted as usually devouring your bauxite supplies.
  • Nethack has several metallivorous monsters; with the help of controlled polymorphing, the player character can try out this diet as well.
  • Pokémon:
    • Aron and its relatives eat iron, which makes them a nuisance to railroads.
    • Nosepass apparently uses its magnetism to attract its prey to it, which suggests that it eats mineral-based creatures.
    • As mentioned above in the Anime section, Meltan dissolves and consumes metal for energy.

    Webcomics 
  • Goblins: Klik comes from a race where every member has a "positive" that heals them and a "negative" that hurts them. Klik's positive is metal, meaning it can consume any metal item to heal itself of almost any injury.
  • Monsters Can Be Heroes Too: Coal eats minerals. Lime is also able to eat metal. When the party gets their first quest reward, they have already started eating the coins before Shelly can say they should save some to buy armor and weapons.
  • Rusty and Co.: Rusty the Monster Adventurer is a Dungeons & Dragons rust monster — a large insect who eats by dissolving metal with his antennae. He's singleminded to the point of having "Eat [item]?" as a Catchphrase, but can put the ability to good use, like eating an attacker's blade mid-swing.

    Web Original 
  • On Neopets, some food you can give the pets contains metal, such as nuts and bolts. These are said to be palatable but unpopular for most of the pets, except the robots.

    Western Animation 
  • In Ben 10: Alien Force, Big Chill is shown to have a preference for eating metal and anything made of metal, which means almost all of Bellwood city is a giant buffet for him. It's later revealed he has been using said metal he consumes to construct a nest for his babies (he's a Truly Single Parent) and when they hatch the metal serves as an adequate food source for them.
  • In Dexter's Laboratory, the titular character is shown in the episode "A Boy and His Bug" to own a genetically-enhanced termite that eats metal instead of wood, especially the metal scraps left over from when Dee Dee destroys his lab.
  • DuckTales (1987): "Attack of the Metal Mites" has Flintheart Glomgold unleash a swarm of bugs called Metal Mites in hopes they can literally consume all the gold in Scrooge's money bin. At one point Gizmoduck attempts to stop them, but the bugs manage to eat the Gizmosuit. The bugs are finally stopped when it turns out they can be restrained by magnets due to all the metal the bugs ate. In the end, Scrooge manages to use the bugs as a way clear out the metal from demolished buildings, and Glomgold ends up having to trying to stop the a few of the bugs from eating his fortune.
  • DuckTales (2017): In "What Ever Happened to Della Duck?", Della's spaceship is repeatedly damaged by an arachnid-like Moon Mite. When she confronts the creature, she discovers that it needs the metal from the ship to feed its young.
  • The Garfield Show: Subverted in an episode where Garfield gives a goat a tin can so it could lick the glue off it, only for the goat to think he's trying to feed it the can and attack him.
  • In Lilo & Stitch: The Series, Experiment 586 (aka. Tank) is designed to eat metal...and grow larger in size each time he feeds. When first introduced, he grows just slightly larger than he was after activating when he eats a small portion of metal, then grows to about the size of a rhino or elephant after eating an entire factory, and then later grows even bigger after eating an immensely large amount of metal afterwards.
  • Looney Tunes: In "Drip-Along Daffy", Daffy Duck aims his gun at Nasty Canasta, who responds by biting it in half and chewing it.
    Daffy: Probably didn't get his iron today.
  • Darkwing Duck features a race of hat-like alien Puppeteer Parasites that love to eat metal whenever they possess a host.
  • Muzzy in Gondoland: Muzzy is a green, furry alien who eats metal objects, especially clocks and similar machines. He has a massive appetite for them.
  • The New Adventures of Superman: In "The Iron Eater", Superman battles a shape-shifting alien creature that emerged from a fallen meteorite and devours iron structures.
  • Popeye: In The Hungry Goat (1943), the eponymous goat seems to actually prefer metal, cans or otherwise, for its food. Of course, this causes no end of trouble for our hero, whose Navy ship the goat decides to eat. The single, rather small goat simply boards the ship and rapidly consumes anything it can get its teeth on, including an enormous length of chain that just vanishes into negative space.
  • Rocky and Bullwinkle: In one story arc of , our heroes are menaced by Metal Munching Moon Mice, large robotic rodents sent by Boris to eat the nation's TV antennas.
  • Samurai Jack: In the second segment of the episode "Jack Tales", Jack meets a family who expresses desire to eat his sword. Upon fighting them, he slices the face of one of them revealing them to be robots. Once their own metal is exposed, they start eating each other.
  • She-Ra and the Princesses of Power: Played With in "Princess Scorpia", when Scorpia sets out a dog bowl of nuts and bolts for Entrapta's robot, Emily. She's "still not sure" if it actually eats.
  • The Simpsons:
    • Averted when the family goes to a petting zoo. Homer tries to get a goat to eat a tin can and it won't do it.
    • Then there's the two-headed crime-solving goat. One head eats tin cans and the other eats health food.
  • Superman: The Animated Series: During Superman's first fight with Lobo in "The Main Man — Part 1", Lois Lane tries to help the downed hero by striking Lobo with a lead pipe. Lobo is unfazed by the attack, then grabs the pipe and eats the whole thing with comical speed.
  • In Teenage Mutant Ninja Turtles (1987), a dinosaur-like creature from Dimension X called a Zipp has an endless appetite for metal. Even worse, eating copper makes it multiply. Eating chocolate re-merges them into one, but into a giant Zipp. The only way to make a Zipp vanish and/or shrink is for it to eat an extremely rare metal called Regidium.
  • Transformers:
    • The scraplets are mechanical parasites that transform between a humanoid form and nuts and bolts. They appear in Genaration 1 comics published by Marvel Comics and the Transformers: Prime cartoon.
    • Unicron, from various continuities and media of the franchise, is a mechanical planet able to transform into a humanoid robot. He is a Planet Eater who devours other mechanical planets and its robotic humanoid inhabitants.
    • The Dinobots fed on the robotic aquatic wildlife of Cybertron in "Grimlock's New Brain", with Slag stating it was a regular thing they did. Grimlock's bio stated that he would eat hapless Decepticons he defeated and in the 1986 movie famously declared "Me, Grimlock, want to munch metal!" when confronting the Sharkticon horde. Several Decepticons also devoured metal and unfortunate Autobots, including the Terrorcons Hun-Gurrr and Sinnertwin.

    Real Life 
  • There are certain extremophile single-cell organisms that feed directly on metal. Among them are:
    • Halomonas titanicae is a deep sea bacteria that feeds on iron. It was so named because it was found to be the source of the "rusticles" forming on the wreck of the RMS Titanic.
    • The Cupriavidus metallidurans is able to eat toxic forms of gold and turn them into inert nuggets.
  • Because gold is usually a non-reactive element, it is safe for humans to consume and has occasionally been incorporated into food and drink for millennia. But the non-reactivity also means that it has no nutritional value or flavor either, so any chefs who put gold into/onto their dishes do so only for the visual aesthetics and/or Conspicuous Consumption.

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