wide range of temperatures. Individuals have survived temperatures as high as and as low as , though growth and reproduction are restricted to the range from . It can also live without air for about six weeks, using up its stored glycogen reserves. Dispersal to new habitats occurs both during the free-living larval stage, by floating timbers carried along by currents, and, historically, from the hulls of wooden vessels. In the Baltic Sea, there were several mass occurrences in the 1930s and 1950s. Biology Food particles, mostly timber raspings but also some microalgae, are extracted from the water passing through the gills where gas exchange also takes place. The gills also contain symbiotic nitrogen-fixing bacteria, which produce enzymes that help to digest the cellulose in the wood. Waste, reproductive gametes, and larvae are discharged through the back of the burrow, which is open to the sea through a narrow aperture. Teredo navalis is a protandrous hermaphrodite. All individuals start their adult life as males, becoming mature when they are a few centimetres long, releasing sperm into the sea. In warmer areas they change into females about eight to ten weeks after settling, but this change may take six months before it occurs in colder climates. The eggs are fertilised when sperm gets sucked into the burrow of a female through the inhalant siphon. More than a million larvae at a time are brooded in the gill chamber, after which they are released into the sea as veliger larvae. By this time they have developed a velum, a ciliated locomotory and feeding organ, and the rudiments of a straight-hinged shell. They eat phytoplankton and disperse with the current for two to three weeks. During further larval stages they develop siphons and gills. When they are ready to undergo metamorphosis, they search for suitable timber on which to settle. They seem to be able to detect rotting wood and are able to swim towards it when they are close enough. Each one then crawls around until it finds a suitable location, where it attaches itself with a byssus thread. It may secrete an enzyme to soften the wood before starting to dig with its foot. When it has formed a hollow, it undergoes a rapid metamorphosis, shedding and consuming the velum and becoming a juvenile shipworm with small horny valves at the anterior end. It can then begin to dig more efficiently.