雅思阅读 085: The Metal Snail — Life on the Edge of Deep-Sea Mining

Adapted from "Meet the endangered scaly-foot snail, the most metal animal in the world" by Adam Kovac, Scientific American, 15 May 2026.

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Reading Passage

Almost three kilometres beneath the Indian Ocean, a hydrothermal vent spews toxic sulfur into inky black water. On its lip, a small snail is not only tolerating the poison but converting it into a shell made partly of iron. The scaly-foot snail (Chrysomallon squamiferum) is perhaps the world's most metal animal.

Despite its toughness, the species has a precarious future. In 2019 it became the first animal that lives on hydrothermal vents to be classified as endangered by the International Union for Conservation of Nature (IUCN). The threat is deep-sea mining companies that want to harvest the minerals at the vents the snails call home.

For decades, scientists assumed that the intense pressure and toxic chemicals at hydrothermal vents could not support life. Then, in 2001, researchers found the snails thriving among a host of other creatures in these extreme environments.

The snail does not eat in the conventional way. Instead, like many vent species, it hosts bacteria in its gut. The bacteria feed on hydrogen sulfide, oxygen and carbon dioxide, converting them into sugar. In return for housing the bacteria, the snail uses that sugar for energy. The bacteria produce toxic sulfur as a waste product. To protect itself, the snail excretes the sulfur, which reacts with iron in the vent water to form a shell that is literally part metal.

"The iron armour is not for defence, as people thought for many years," says Chong Chen of the Japan Agency for Marine-Earth Science and Technology. "It is a by-product of symbiosis."

The snail is less than five centimetres long. It exists on only eight hydrothermal vents worldwide — a total habitat about half the size of Disneyland. It is also the only animal known to incorporate iron sulfide into its shell.

Those same vents are rich in copper, zinc and gold — minerals coveted by mining companies. Demand for copper is soaring because of its use in AI data centres and renewable energy. Although no deep-sea mining is under way in the snail's habitat yet, at least two of the eight vents have been considered for possible operations.

Chen suggests that companies could mine inactive vents instead, which no longer host the snail. But he warns that inactive vents may also support unique species.

Beyond its own intrinsic value, Chen notes that hydrothermal vents play a key role in global ocean chemistry, pumping carbon and nutrients into the water. "The world is one connected planet," he says. "Mining hot spots like these may lead to consequences we did not foresee."

Questions 1–5

Choose the correct letter, A, B, C or D.

1. The scaly-foot snail lives at depths of about

   • A. 300 metres.
   • B. 800 metres.
   • C. 3 kilometres.
   • D. 10 kilometres.

2. The snail's iron-rich shell functions mainly to

   • A. defend against predators.
   • B. remove toxins from its body.
   • C. attract a mate.
   • D. help it swim.

3. How many hydrothermal vents worldwide are home to the snail?

   • A. Two
   • B. Eight
   • C. Thirty
   • D. Eighty

4. Why do mining companies want the minerals at the vents?

   • A. The gold is used in jewellery.
   • B. Copper is needed for AI data centres and green energy.
   • C. The iron is used to build ships.
   • D. The sulfur is used in medicine.

5. Chen's suggestion for mining companies is to

   • A. stop all deep-sea mining permanently.
   • B. mine inactive vents instead of active ones.
   • C. only mine in the Atlantic Ocean.
   • D. wait until the snail is extinct.

Questions 6–10

Do the following statements agree with the information?

Write:

• TRUE
• FALSE
• NOT GIVEN

6. Scientists have always believed hydrothermal vents support life.
7. The snail provides a home for bacteria in its gut.
8. The snail is the only animal known to incorporate iron sulfide into its shell.
9. Deep-sea mining has already destroyed three vent sites.
10. The US Army has studied the snail's scales for armour design.

Questions 11–13

Complete the summary. Choose NO MORE THAN TWO WORDS from the passage.

The snail survives at hydrothermal vents through a 11 with bacteria. The bacteria convert chemicals into sugar, producing 12 as waste. The snail excretes this waste, which mixes with 13 in the water to form a metallic shell.

Answers

1. C — "almost three kilometres beneath the Indian Ocean."
2. B — "it helps remove toxins from the snail's body."
3. B — "only exist on eight sulfur-rich hydrothermal vents."
4. B — "Copper is particularly in demand because of its use in artificial intelligence data centers."
5. B — "mining companies could target inactive vents."
6. FALSE — Scientists long assumed vents were incompatible with life.
7. TRUE — "it is home to bacteria that feast on hydrogen sulfide."
8. TRUE — "the single animal known to incorporate iron sulfide into its shell."
9. NOT GIVEN — Mining has been considered, not yet destroyed.
10. TRUE — "The U.S. Army has studied the snail's scales."
11. symbiosis
12. sulfur
13. iron

Key Vocabulary