Thousands of 10-inch worms known as 'penis fish' inundated a California beach. A biologist says they feel like 'slimy water balloons.'

David Ford

Thousands of innkeeper worms on Drake's beach in Point Reyes, California, December 6, 2019.

• A beach in Point Reyes, California was inundated with thousands of marine worms known as "penis fish" on December 6.
• The pink creatures, sometimes also called fat innkeeper worms, usually live under the sand, but they were stranded on the beach after a storm.
• According to one biologist, the worm feels like a "slimy water balloon."
• Otters, rays, and even some people like to eat these marine worms.
• Visit Business Insider's homepage for more stories.

Thousands of 10-inch worms washed ashore on Drakes beach in California's Point Reyes National Seashore last weekend.

Thick and bulbous on one end, with a nipple-like protrusion on the other, the scientific name for these marine spoonworms is Urechis caupo, but they're more commonly known as "penis fish" or "fat innkeeper worms."

Photographer David Ford, who lives in nearby Lagunitas, California, came across the horde of wriggling worms on December 6.

"I had no idea what they might be ... it went on for 2 miles," Ford told Vice. "I walked for another half hour and they were scattered everywhere. There were seagulls lined up the beach the whole way having eaten so much they could barely stand. A quarter of them looked like they were still alive. The rest were dead, they had a dead sea-creature smell."

He snapped a picture and sent it to local biologist Ivan Parr, asking: "What happened?"

Parr published an article in Bay Nature explaining that the curved creatures Ford had seen were, in fact, penis fish.

Castaways after a storm

This particular species of worm - which resembles bulging bratwursts or, yes, male genitalia - is found up and down the US Pacific coast, from Baja California to Oregon. They can grow up to 19 inches long.

According to Parr, the worms probably got stranded above ground after a strong storm forced them out of their sandy underground homes. They usually reside in what's known as the inter-tidal zone: the area of the shore that's exposed at low tide but submerged when sea waters are high.

Steve Lonhart /NOAA/SIMoN Photo Library

A marine spoonworm nicknamed the "penis fish" outside its burrow underwater near Point Lobos, California, 2005.

"Strong storms, especially those tied to El Niño, can wreak havoc on the inter-tidal zones where these worms rest their butts, breaking sand sediments apart, smashing thousands of cozy burrows and leaving their residents strewn across the beach," Parr wrote in Bay Nature.

He told Business Insider that this type of stranding has happened before, in 2010 and 2016, "which were El Niño years with big storms."

The worms have previously washed ashore in Pajaro Dunes, Moss Landing, Bodega Bay, and Princeton Harbor on the California coast.

Parr added that "if there are more frequent, high-energy storms" in the future, more events like the one Ford witnessed are likely.

Burrowing worms

There's a reason for these marine worms' unfortunate resemblance to overcooked hot dogs: They like to burrow up to 2 feet deep into the sand, in U-shaped subterranean tunnels.

One end of this home - the front end - is covered in a net of mucus that helps the worm snag plankton and bacteria to eat. Once those morsels are digested, the animal then discards the leftovers out the back of its burrow by spraying them from its anus.

When it's time to reproduce, the creatures eject eggs or sperm out of their burrows in a similar fashion, Parr said. Then they mix in the water.

Kate Montana, iNaturalist Creative Commons

A beachgoer holds a fat innkeeper worm in Bodega Bay, California, June 2019.

The creatures' innkeeper nickname is a nod to the fact that, like any good innkeeper, these worms provide food and shelter for other underwater denizens. Their tunnels often provide safe harbors for fish and crabs, while the leftovers they toss out the back get eaten by passing shrimp and clams.

The worms are, according to Parr, the consummate host.

A delectable delicacy

Despite their best efforts to hide under the sand, penis fish often get eaten by sting rays, sea gulls, otters, and sharks, Parr said.

"Rays and sharks have this cool way of leaning over and literally sucking them out of their burrows," he said. "Otters, who are very nimble, can easily dig them up."

Humans, too, dine on relatives of the penis fish. Another type of marine worm, called Urechis unicinctus - or "gaebul" as it's known to diners - is found in Pacific waters off the coast of China and South Korea. It's nearly identical in appearance to the fat innkeeper worm and is a sought-after item in some South Korean fish markets.

Wikimedia Commons

Marine spoonworms are sold at a fish market in Busan, South Korea.

Gaebul is typically consumed raw and has a chewy, salty, and surprisingly sweet taste, according to Atlas Obscura. It is often served with a savory sauce made from sesame oil and salt.

Parr said he has never tasted gaebul or its California relative.

"I've held a fat innkeeper worm, but I haven't eaten one yet," he said, adding, "they feel slippery, sort of like a slimy water balloon."

NOW WATCH: There's a place off California's coast called the 'Red Triangle' where over 1/3 of great white shark attacks happen