Crepidula fornicata

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Crepidula fornicata, also known as the common slipper shell or common slipper limpet, is a medium-sized sea snail. The shell is about 2–5 cm long, sometimes up to 5.6 cm. The outside is arched and rounded, and the inside has a white “deck” that makes the shell look like a boat or slipper.

These snails often stack on top of each other, with larger, older females at the bottom and smaller, younger males on top. They are sequential hermaphrodites, meaning individuals can change from male to female as the colony grows.

Native to the western Atlantic coast of North America, Crepidula fornicata ranges from Nova Scotia to the Gulf of Mexico. It has been introduced to many other places, including the Pacific Northwest and Japan, usually via shipping and oyster transfers.

In Europe, this species is invasive in many countries, including Denmark, France, Italy, the Netherlands, Spain, the United Kingdom, Norway, and Sweden. It can damage oyster beds and other shellfish, and there are few natural predators in these new areas. Its northward spread is limited by cold winter temperatures.

The slipper limpet lives in bays, estuaries, and sheltered coastal areas. It can be found from the surface down to about 70 meters, often on rocks, shells, other shells, or dock pilings. It feeds by taking in tiny particles from the water or from detritus.

Breeding happens from February to October, with a peak in May and June. Most females spawn in May or June, and many females will spawn twice a year, especially after neap tides. In a stack, if the bottom females die, the largest male at the bottom can become female.

In the United Kingdom, the common slipper limpet is an invasive non-native species. It is illegal to release them into the sea in England. They arrived in the UK in the late 19th century, carried with oysters from America. Their presence affects native mollusks such as the queen scallop, the edible oyster, and the blue mussel.

Some people see slipper limpets as a potential food source to help reduce their spread. They are eaten in various places around the world and can be cooked in many ways. The liquid produced during cooking can also be used to make broth.