Lewis Moon Snail and Its Freaky Egg Casings Found on Oregon, Washington Coasts

Published 03/12/25 at 7:25 a.m.
By Oregon Coast Beach Connection Staff

(Tillamook, Oregon) – The things that live just beyond sight out there in the ocean are downright freaky. It really can be an alien world down there. (Photos Alyssa Casteel / Seaside Aquarium)

So it should be no surprise that one of those out-of-this-world creatures from the great depths of the Oregon coast would breed in a similarly oddball fashion. The beastie known as the Lewis moon snail looks like something out of the original Outer Limits series, but its egg casings are comparatively enormous and resemble strange clay pots – like what you might've found the Dead Sea scrolls in.

Seaside Aquarium recently bumped into one of these in one of those marshy spots right near the Oregon coast: the egg casing of a Lewis moon snail. The photos taken by the aquarium's Allysa Casteel are rather closeup so they seem extra large, but they're only about six inches in diameter.

Showing these off on social, the aquarium said it may look like garbage, and no it's not an alien (although they then backtracked a bit and admitted “well, maybe” a little alien). At six inches, these casings are unusually large for snail eggs, really, hosting thousands of the little babies.

How is this is done? It's going to again go back to something out of the Outer Limits.

“Held together by mucus and sand, the developing embryos are laid carefully in what is called a ‘Sand Collar,' “ the aquarium said.

Essentially, the eggs are surrounded by sand and held together by that mucus excretion from the moon snail. The moon snails spend most of their time pretty far out there, then come back slightly inland in summer when they mate.

“These egg collars can reach nearly 6 inches in diameter,” said the aquarium's Tiffany Boothe. “You will not find these collars on open sandy beaches, you'll have to search intertidal mud flats like those found in Tillamook and Netarts Bay.”

The sand dissolves away after several weeks and then the larvae hit the water. Baby Lewis moon snails (Neverita lewisii) head for deeper depths and along the way feed as herbivores, eating more plant-like things such as diatoms. After a time, they become meat eaters.

They become quite the predators.

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“Lewis moon snails are a predatory snail that prowl the intertidal zone down to depths of 600 feet, drilling holes in bivalves and sucking the goodies out,” the aquarium said.

They're found all over shoreline environments of the Oregon and Washington coasts, and when fully relaxed and extended they stretch out around a foot or more.

“The Lewis moon snail is one of the largest snails found intertidally in the Northwest,” Boothe said. “When fully extended it is hard to believe that this large snail is capable of retracting fully into its shell. Much of their body expansion and contraction is due to water. The foot and mantle have hollow sinuses which water can be pumped in to expand their body.”

All that is crammed inside a shell that reaches up to five inches in diameter.

“And the snail itself can live for up to 14 years,” Boothe said.

These aren't a common find on this coastline, however – partially because most don't really wander the tidal mud flats adjacent to the beach. Seaside Aquarium got lucky, and luckily for everyone they have a moon snail on display in their tanks.

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