It bores deeper into the wood and spends the rest of its life as a tunneller. Economic effects Teredo navalis is a very destructive pest of submerged timber. In the Baltic Sea, pine trees can become riddled with tunnels within 16 weeks of being in the water and oaks within 32 weeks, with whole trees in diameter being completely destroyed within a year. Ships' timbers are attacked, wrecks destroyed and sea defences damaged. Around 1730 in the Netherlands, shipworms were found to be seriously weakening the wooden dike revetments, and to prevent erosion of the dikes and subsequent flooding disasters the revetments had to be replaced with heavy stones, at great expense. The shipworm's arrival in San Francisco Bay around 1920 heralded great destruction to the piers and wharves of harbours. It has spread in the Pacific Ocean where its greater tolerance of low salinity levels has caused damage in areas previously unaffected by native shipworms. In the eighteenth century the Royal Navy resorted to coppering the bottoms of its ships in an attempt to prevent the damage caused by shipworm. No treatment of timber to prevent attack by Teredo navalis has been completely successful. Experiments by the Dutch in the 19th century proved the inefficacy of linseed oil, metallic paint, powdered glass, carbonization (burning the outer layers of the wood), and any of the usual biocides such as chromated copper arsenate. They also attempted covering wooden pylons with precisely arranged iron nails, but this too had no lasting effect. In 1878 it was discovered that creosote was an effective deterrent, though to work best it had to be applied to soft, resinous woods like pine; in order to work on harder woods such as oak, special care had to be taken to ensure the wood was completely permeated by the creosote. Submerged wrecks have been protected by wrapping them in geotextiles to provide a physical barrier to the larvae or by reburying them in the sediment. No permanent solution has been found. References navalis Molluscs described in 1758 Taxa named by Carl Linnaeus Molluscs of the Atlantic Ocean Edible molluscs Brazilian cuisine Thai cuisine