How the Lowly Shipworm Changed History

When the Spanish Armada attacked England in 1588, Queen Elizabeth I’s forces received help from an unassuming ally. Unbeknownst to the Spanish, shipworms had been eating away at their formidable 130-ship fleet. With weakened hulls, their vessels proved more vulnerable to both English cannonballs and storms that tore them to bits off the Irish and Scottish coasts.

Shipworms don’t tend to get much credit for the Armada’s defeat, which shifted the balance of power in Europe. Yet England might not have won without them. “[A professor of mine] used to be fond of saying, ‘If it wasn’t for shipworms, we’d all be speaking Spanish,’” says Dan Distel, director of Northeastern University’s Ocean Genome Legacy Center.

Shipworms bedeviled not just the Spanish Armada, but also some of the world’s most famous mariners. Since at least as far back as ancient Greece, humans have been devising methods of keeping infestations at bay. Even so, they continue to cause significant economic damage each year, annihilating docks, dikes, wharves and piers throughout the world. “Shipworms are the main reason we don’t use wooden structures in the water anymore,” Distel says.

Though they resemble worms, shipworms are actually bivalve mollusks, like clams and mussels. Unlike other bivalves, however, their two shells surround only their mouths and have ridges used to excavate wood—their main source of food. “You can think of it as sort of a helmet,” says Barry Goodell, a retired microbiologist and biochemist at the University of Massachusetts Amherst and co-author of a 2024 study on how shipworms digest wood. Goodell adds that most shipworm shells are no bigger than a human fingernail, even as the bodies of the largest species grow up to six feet long.

As larvae, shipworms are free-swimming. But once they burrow mouth-first into a log, hull or pier, they can’t get out. “They are locked into that piece of wood for their lifetimes,” Goodell says. Eventually, they can devour their own home, leaving themselves for dead.

Shipworms are among the planet’s premier recyclers of wood that reaches the ocean. “If we didn’t have organisms like shipworms, all that wood would eventually pile up,” Goodell says. Fish and other marine animals also eat their larvae, millions of which can be produced by a single female. Yet despite their ecosystem services, shipworms have likely been terrorizing humans since the invention of the first oceangoing boats.

Sometimes known as the “termites of the sea," shipworms create pinhole-size entrance punctures that are hard to notice from the outside. They then essentially rot wood from the inside out, capable of ravaging the bottom planks of boats so thoroughly that they “could easily crumble even due to a mild impact," write researchers in the 2014 publication, Shipwrecks and Global "Worming."

On his fourth and final voyage to the New World, Christopher Columbus got a firsthand taste of the chaos shipworms could wreak. After reaching present-day Panama in 1503, he tried to sail back to Spain, only to find that his vessels had been honeycombed by shipworms. “With three pumps, pots and cauldrons and all hands at work,” Columbus wrote, “I still could not keep down the water that entered the ship, and there was nothing we could do to meet the damage done by the shipworm.” He barely made it to Jamaica, where he and his crew were then marooned for a year before getting rescued.

Though the English benefited from shipworms when fighting the Spanish Armada, at other times they found themselves at the mollusk’s mercy. Historical writings suggest that the boats of King Richard I were attacked by shipworms during the Third Crusade, and that prominent English captains Sir Francis Drake and James Cook also survived shipworm infestations.

In 1678, French naval commander Jean d’Estrées wrecked several vessels in the Caribbean during the Franco-Dutch War, with shipworms suspected as the primary culprit. Overall, shipworms likely contributed to the sinking of thousands of ships before steel and fiberglass hulls largely replaced wood in the 19th and 20th centuries. “They say sailors were more afraid of shipworms than pirates,” Distel says.

Besides vessels, shipworms like to gorge on wooden docks, seawalls, wharves, piers, pilings, buoys, floats, railroad trestles, lobster pots and other fishing gear. In the 1730s, they destroyed the dikes protecting the Netherlands from floods, forcing the Dutch to install expensive stone replacements and fueling political upheaval.

Shortly after World War I, the San Francisco Bay Area suffered a massive shipworm infestation. One source estimates that, at its peak, a major wharf, pier or ferry slip collapsed every two weeks. A 1,000-foot section of wharf fell in a single day in 1920. The shipworms even purportedly caused loaded freight cars, grain warehouses, railroad bridges and a highway to crash into the water.

Other U.S. port cities that have experienced shipworm outbreaks include Los Angeles, Boston and New York. Distel recalls being contacted by a harbormaster in Maine about some pier structures that had caved in. “They thought a boat had come in and hit them overnight.” But the culprit turned out to be shipworms.

In the 4th century B.C., the Greek naturalist and philosopher Theophrastus made one of the first known references to shipworms, warning of their permanent harm. Alexander the Great’s followers supposedly found a tree resistant to them in present-day Bahrain. Centuries later, the Roman naturalist and military commander Pliny the Elder, and the Roman poet Ovid, both wrote about shipworms. Pliny expounded on the sound of their shells drilling and described protecting ships with beeswax and resin. The Greeks and Romans also tried sheathing their ships with lead and coating them with tar or pitch, whereas the Chinese combined lime, chopped hemp and wood oil into a glue-like protectant, according to Marco Polo.

Other strategies employed by civilizations ranging from the Egyptians to the Phoenicians included metallic paints, animal hair or copper sheathing and double-bottomed hulls. Whale oil and other animal fats were purportedly used in various mixtures, and fires were lit to steam shipworms out. Sometimes ships were simply hauled ashore or moved into shipworm-free freshwater. (In fact, the English Navy is believed to have suffered far less shipworm damage than the Spanish Armada in 1588 because its fleet overwintered on a river.)

Various chemicals, heavy metal salts and plastic coverings have also been used to stave off shipworms. In the 1800s, hundreds of anti-shipworm patent applications were submitted in the United States alone. Canadian logging companies reportedly exploded dynamite to generate shock waves that killed the voracious wood borers. Yet no shipworm deterrent was 100 percent effective at protecting wood, and some came with major drawbacks, such as dangerous toxicity.

In one of the earliest examples of aquaculture, Aboriginal Australians began cultivating shipworms for food roughly 8,000 years ago. To this day, they remain popular in parts of Southeast Asia and Brazil. In the Philippines, for example, they’re called “tamilok” and eaten raw like sushi, whereas in Thailand they’re called “priyang talay” and are typically prepared in curries or stews.

Research shows that they grow faster than other bivalves and that they’re rich in nutrients. They also have a lower environmental cost than meat and fish and could conceivably be farmed commercially. The bacteria found in shipworms are even a potential source of new antibiotics.

“In essence, we can take a completely sustainable resource, wood, and convert it into high quality protein at industry-leading rates,” Reuben Shipway, a shipworm biologist and start-up founder states. “They once ate our ships, now we can eat them."