Native oysters are gregarious animals, and start their lives as males. They mature sexually as males between eight and ten months old. From then on, oysters will change sex regularly, depending on the water temperature. If the temperature reaches 16°C, they become females every three or four years. If the temperature reaches 20°C, they will change to females each year. They only revert to being males during the cooler intervening periods. Oysters may live for as long as 15 years but the usual lifespan is thought to be around six years.
Eggs are stored and fertilised in the gill cavity of the female and remain there for a week before becoming free-swimming larvae and being released. The sperm is passed through the gills as part of the normal feeding process. The oyster larvae join the plankton in the open sea until, after 10 or 20 days, they find a surface to attach themselves. Adult oysters feed by filtration, sieving out the plankton using their gills.
The towns of Colchester in Essex and Whitstable in Kent have become famous for their Oyster Festivals. Oysters have been an important food source since prehistory, and during the Roman occupation, British oysters were exported in large quantities back to Italy. One claim for eating them is that they act as an aphrodisiac, although there is no scientific proof for this argument.