For most of human history, shipworms, aka Teredo worms, have been a bane to mariners. Technically a clam rather than a worm, shipworms, which burrow into and destroy wood in seawater, have been known and feared from the time humans began traveling on the seas. Ancient Egyptian and Phoenician seafarers are known to have coated the hulls of their vessels with wax in an attempt to mitigate shipworm damage. In the Classical Period, Greek and Roman sailors used pitch, tar, and lead sheathing to deter the shipworms. Warships, for which those methods were unsuitable, were beached and dragged ashore when not in use.
Shipworms continued to plague sailors in the Age of Exploration. Most famously, on Columbus’s return from his fourth voyage to America two of his ships were destroyed by shipworm damage and the other two had to limp into Jamaica where they were stranded for months. Captain Cook lost a ship to shipworm damage and many historians believe shipworm damage was a contributing factor in the defeat of the Spanish Armada. Shipworms weakened the hull of the Essex, which was rammed and sunk by a whale in 1821, inspiring Melville’s Moby Dick. According to at least one historian, throughout history shipworms have sunk more ships than pirates.
In their never-ending battle against the shipworms, sailors continued to coat the hulls of vessels, trying a wide variety of coatings, including tar and leather. Shipbuilders also began constructing double-hulled ships, with a false outer hull, which the worms/clams could eat harmlessly. In the 18th century, the British navy began sheathing its ships with copper, an important technological innovation that not only protected the ships from shipworms, but also had the unintended benefit of making them faster than their unsheathed opponents, which played a major role in the British navy becoming the world’s most dominant.
The damage caused by Teredo worms was not confined to ships. Piers, docks, buoys, and wooden seawalls have also been their victims. During a shipworm population explosion in the 1730s, shipworm damage to the wooden piles in the Dutch seawalls caused a major crisis there, which was resolved by replacing the wood with stones. (It was during this surge of shipworm damage in Europe that the British navy began using cooper sheathing, changing the course of world history). In 1902, shipworm damage caused the wooden support beams on a dock in Tampico, Mexico to collapse, killing at least 60 people.
With the advent of steel and fiberglass hulls and building material, shipworms are no longer as feared and threatening has they have historically been, although they are still estimated to do about $1 billion in damages each year worldwide. Interestingly, scientists are still trying to determine exactly how the worms/clams digest wood, an answer that has proven surprisingly elusive.
The image is an 1834 illustration of a shipworm (Teredo navalis) and some shipworm-eaten wood.