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What Is That Freaky Trilobite Thing in Oregon Coast / Washington Coast Caves?

Published 07/28/22 at 6:15 PM PST
By Oregon Coast Beach Connection staff

What Is That Freaky Trilobite Thing in Oregon Coast / Washington Coast Caves?

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(Manzanita, Oregon) – You're wandering the beaches on a lovely day, somewhere on the Oregon coast or Washington coastline. There are a handful of caves or crevices in the rocks to explore, at places like, say, Bandon, Ruby Beach in Washington or Hug Point near Cannon Beach. You saunter into that cave and suddenly – boom – there's a giant, primeval-looking bug skittering about. (Photos courtesy Seaside Aquarium unless otherwise noted)

Ewwww! Gross!!! It's disgusting and you can hardly believe it's real. In fact, it looks a lot like a trilobite, an anthropod that's been extinct on Earth for a good 500 million years. You start looking around for some temporal anomaly that brings in dinos, like that old Brit sci-fi show Primeval. Or maybe a sighting of Prof. Nick Cutter.

What you're looking at is a strangely common kind of crustacean (actually an isopod) called a sea slater (Ligia pallasii), or sometimes known as a sea roach or sea louse. Yummy!

You don't often see them on beaches: they primarily hide under things like logs, in rock crevices and so on. But they exist in a lot of places, and locals complain about seeing them a lot in their yards. Yet when you do see them, shrieking is an understandable reaction.

An isopod means they’re a crustacean with seven pairs of legs. There are several species of them that skitter around the Washington coast or Oregon coast, and each is fairly similar to the rest. Some come in different colors and shapes, and others prefer slightly different environments. With the sea roach / louse / slater, they lean towards cliffs and their holes, like big cracks or caves.

According to Seaside Aquarium’s Tiffany Boothe, they’re nocturnal, which means they generally only come out at night.

“They spend most of their day hiding in dark crevices and abandoned caves but at night they emerge in search of dead plants and animals to feast upon,” she said.

Again: yummy!!! Though this could be ripe with prank ideas during your next nighttime beach bonfire.

It's fairly common to see some scurry away after you turn over a rock. If you check big cracks close enough, there's a good chance you'll see one. However, sea slaters don't hang out in the sand, Boothe said. They prefer higher areas above the beach in rocks and cliffs.

You can see them on occasion rushing around in the shade at the bottom of some log you're sitting on. That's a bit disconcerting, but it can be ignored. The creepy thing happens when you're sitting on a log at night and some of them brush past you. Yuck-o-rama.

“Though they may startle you as they scurry across rocks in the high intertidal zone, they are an important food source for birds and small crabs,” Boothe said. “Not all isopods are as ugly as the sea slater. Some, like the Rockweed Isopod (Pentidotea wosnesenkii) are actually quite beautiful and range in color from bright green to modeled pink.”

These crusty little guys are not marine creatures, Boothe said. Considered terrestrial, they breath air only.

The sea slater usually gets about an inch to an inch and a half long.

And yes, they are somewhat related to “sow” bugs you'll see in your yard, the things known as “rolly-pollies” or potato bugs. But that's a different creature, in actuality.

Sure, they're ugly, Boothe admits, and they remind people of cockroaches, albeit with a touch of Jurassic Park. They're an important part of the beach ecosystem. Some of those even nastier dead, decaying and smelly things you encounter on the Oregon coast or Washington coast disappear with the help of these beachside weirdos.

As an aside, there are technically no (or almost no) trilobite fossils in Oregon. There are fossilized chitons found in Bend that look like trilobites, however.

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Hug Point: the contents of this crevice contains skittering surprises (Oregon Coast Beach Connection)

Also distantly related to the rock louse is Gray Whale Lice (Cyamus kessleri), which lives on whales. They're a good thing for the whale, actually. Photo Seaside Aquarium

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