An evening stroll in Esquimalt乌鸦传媒檚 Macaulay Point Park took a horrifying turn for one man and his dog when they found themselves surrounded by 乌鸦传媒渆vil-looking worms.乌鸦传媒�

More used to spotting harbour seals, river otters and herons on his daily walk with his French bulldog Wednesday, Greg Gilks says he was not prepared for what he saw in the waters at the park乌鸦传媒檚 wharf.

乌鸦传媒淚n every direction there were just hundreds of them,乌鸦传媒� he said. 乌鸦传媒淚t was crazy 乌鸦传媒� they looked like some sort of giant sea centipede.乌鸦传媒�

Alone, under the cover of darkness and with a chill wind blowing, Gilks says it felt like he had stepped into the scene of a horror movie.

乌鸦传媒淚t had a 乌鸦传媒楾he Thing乌鸦传媒� vibe to it,乌鸦传媒� he said, referencing the science-fiction horror film where a group of researchers in Antarctica are hunted by a parasitic alien creature.

Was life imitating art? Were Gilks and his dog in danger of assimilation by shape-shifting extraterrestrial sea creatures?

No, of course not. But while their encounter was not paranormal in nature, it was a phenomenon, says Benjamin Neal, assistant teaching professor in biology at the University of Victoria.

The mysterious creatures are polychaetes, most commonly known as giant pile worms, or giant clam worms, says Neal, who thinks the species Gilks saw could be either Nereis brandti or Nereis vexillosa.

乌鸦传媒淭hey are common around here, especially west of town, around Sooke and farther up the west side,乌鸦传媒� he says. 

Brandti is the bigger of the two, growing to around 20 centimetres in length 乌鸦传媒� vexillosa, while still big in size, are slightly smaller, he explains.

Buried in the sand at the bottom of the sea, the giant pile worm leads a life out of sight from humans. 

But once a year, triggered by the tides, lunar cycle and pheromones in the water, the worms swarm en masse, rising to the surface to reproduce.

It was this phenomenon Gilks 乌鸦传媒渕ost likely乌鸦传媒� witnessed in the waters of Macaulay Point on Feb. 1.

乌鸦传媒淵ou're lucky to witness this interesting, beautiful thing for sure,乌鸦传媒� Neal said.

Once at the surface, the worms release eggs and sperm openly into the ocean, where fertilization takes place. Little larvae quickly develop and start feeding on phytoplankton before dropping to the bottom of the sea to continue their development.

The exact cause for the synchronized natural event is not confirmed, says Neal.

乌鸦传媒淚t is mysterious, beautiful stuff,乌鸦传媒� says Neal. 乌鸦传媒淗ow do they know that's the particular time they rise up? It could be a chemical cue, it could be a light cue.

乌鸦传媒淚t is a very coordinated event 乌鸦传媒� there's a lot going on.乌鸦传媒�

And the timing is critical for the phenomenon to be successful, as the giant pile worms are semelparous: they reproduce once before dying.

乌鸦传媒淪uccess depends on them coming up in a swarm, because if one individual goes up and releases their gametes, it's not going to work,乌鸦传媒� says Neal. 乌鸦传媒淪o you want to make it count.乌鸦传媒�

The reproductive strategy explains what Gilks found when he returned to the scene at Macaulay Point Park the next day.

Washed up on the shore were hundreds of worms, some showing signs of life, others lifeless.

乌鸦传媒淚t was really gross looking,乌鸦传媒� he said.

In the Pacific northwest, mating swarms for Nereis vexillosa usually occur in late winter or spring.

乌鸦传媒淚t strikes me as odd that they would be spawning on a very cold day with a half a moon in February, that乌鸦传媒檚 slightly unusual,乌鸦传媒� says Neal. 乌鸦传媒淏ut the lights on the docks may have been a factor.乌鸦传媒�

While not overly concerned about the "odd" timing of the mass spawning event on Feb. 1, Neal notes the timing of natural phenomenological events in other parts of the world is showing changes because of climate change and development.

乌鸦传媒淏ird migrations can be impacted by lights,乌鸦传媒� he said. 乌鸦传媒淭urtle egg laying behaviour is highly affected by lights in Florida and Central America. So it's not a huge stretch to say lights could be affecting the pile worms.乌鸦传媒� 

乌鸦传媒淓verything we do could have an impact on these tightly choreographed kinds of natural phenomenon,乌鸦传媒� he adds.