Periwinkles (Littorina spp.)

Description: Periwinkles are the group of smaller snails commonly found at Haystack Rock. Most of them are dark blue to black and very small. A few do come in colors of dark green, dark brown, or gray. Some species may have white spots, a checkered pattern, or spiral bands. Baby hermit crabs sometimes live in periwinkle shells when they are too small to use other snail shells. Most species in this group are less than 2 cm long.

Habitat: Different species of periwinkle have different habitat ranges but all are found in intertidal zones. Some ranges are from Alaska to Mexico while others are Alaska to Oregon. At Haystack Rock, periwinkles can be seen across tidal zones, but there are large concentrations in the upper tidal zone on algae covered rocks in the marine garden. 

Diet: These small snails scrape tiny pieces of algae off of rocks using their radula - a ribbon shaped tongue that is lined with teeth. They may also eat tiny zooplankton or larva if given the opportunity.

Tide Pool Tidbits:

• Shore birds, sea stars, crabs, and larger snails are known predators of periwinkles.

• Common species at Haystack Rock include checkered periwinkle (Littorina scutulata), little checkered periwinkle (Littorina plena), Sitka periwinkle (Littorina sitkana), and sometimes the salt marsh periwinkle (Littorina subrotundata).

• Sitka periwinkles don’t travel far, typically moving less than 1 m every month.

• Some people believe that land snails evolved from periwinkles.

Reference: The New Beachcomber’s Guide to the Pacific Northwest by J Duane Sept