Oyster beds or reefs are very productive marine habitats providing shelter and subsistence to a wide variety of organisms. Many species of marine worms can often be found living on the outer surfaces of oyster shells. Worms are often found inside small calcareous tubes they form on the shell surfaces as well inside the natural crevices of the shells.
These worms can vary greatly in size, but typically do not exceed two inches in length. (The first photograph shows a mud worm often found on unwashed oyster shells while the second photo represents a variety of worms that may be found on the outer surface of oyster shells).
When oysters are shipped with no or minimal washing worms will routinely remain associated with the outside of oyster shells. Occasionally cleaned oysters will also retain some live worms that are enclosed in tubes or inside crevices.
When live oysters are roughly handled, as in cleaning and preparing at food service establishments, any associated worms will often make an appearance. To consumers not accustomed to seeing these organisms this can often cause considerable concern.
Such worms are generally not parasitic to oysters or any other organisms and are merely associated with oyster shells for protection. They do not affect the health, quality or taste of oysters, and they do not pose a known health risk to consumers, especially if they are discarded when found.
To help avoid concerns with such worms, oysters should be obtained from suppliers that thoroughly clean the oysters prior to shipment. Oysters should also be washed in cold, clean, running water prior to serving as an added step, and any worms that are found should be removed and discarded.