Teredos are a genus of highly specialized wormlike molluscs that are extremely destructive to wooden vessels and waterfront installations.
Before the advent of man, teredos lived in fallen trees in the sea. When man began building wooden ships and wharves, teredos became pests. Archimedes of Syracuse protected his ships by a sheathing of lead. Copper sheathing was first used by the British in 1758 to protect their ships (from teredos, borers and fouling organisms). In the days of the clipper ships, nearly all vessels sailing in tropical seas were sheathed with copper, a very expensive practice, but with the advent of metal ships the problem of teredos ended. Teredos are still a problem for wooden ships, small fishing and pleasure boats, and specialized ships such as minesweepers. For waterfront installations, teredos are a significant though decreasing problem as more and more wharves and piers are constructed of steel and concrete. The Dutch were the first to be greatly concerned at such destruction. In the 18th century, severe infestations of teredos, attacking the wooden parts of locks and dykes, threatened the existence of much of their countryside. Of the most recent attacks by teredos, the most famous was that in San Francisco bay during 1917-21, when $25 million worth of destruction was caused to wharves and jetties.
Teredos are worldwide in distribution, generally living in marine or brackish water, though occasionally in fresh water. Since earliest times they have been of concern to maritime people. The damage that teredos do is not readily seen; the outer surface of the wood may look undamaged and yet the interior may be completely riddled; hence the description 'termites of the sea'. Teredos are able to survive within wood for long periods of time during adverse conditions, including reduced salinity, pollution and silting. Furthermore, despite many advances made during this century in teredo control, there is still no permanent protection against them.