The Question: I was recently vacationing in Victoria and was so enchanted by the incredible creatures on the beach. What incredible life! I was wondering what makes the little swirls of sand that spiral up like little mounds. It looks almost like worm poop.

Submitted by: Audrey, British Columbia, Canada

The Short Answer: Your worm poop instincts are good. The swirls are indeed the “castings” of a worm. Various species of lugworms are found in sandy marine mud all over the world. Based on your location on the northwest coast of North America, the ones who made the swirls you saw were probably Abarenicola pacifica. The worms live in a U-shaped or J-shaped burrow. They ingest the sandy mud at one end, and excrete digested sand at the other. They can process a cubic centimeter or more of sand every hour. The worms digest the bacteria and other microorganism in the sand, in much the same way that earthworms process soil.

Here is a short video of Abarenicola pacifica that shows them casting underwater: http://vimeo.com/40197385

Lugworms are a favorite bait of fisherman all over the world, and in this video, you can see a fisherman collecting lugworms by using a sand pump: https://www.youtube.com/watch?v=dzfCbmLnLKE

For more information about Abarenicola pacifica, go to: http://www.asnailsodyssey.com/LEARNABOUT/LUGWORM/lugwBurr.php

Interesting Escape mechanism:
Fishermen aren’t the only ones who like lugworms. They are eaten by shorebirds and also by fish when the tide covers them. When a bird or fish grabs a lugworm, the lugworm often releases its tail, similar to the way a lizard escapes from predators by releasing its tail. If a lugworm loses its tail, it can regrow it.

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"What made these swirls in the sand?." Ask a Naturalist® - Accessed November 25, 2020. http://askanaturalist.com/what-made-these-swirls-in-the-sand/
"What made these swirls in the sand?." Ask a Naturalist® [Online]. Available: http://askanaturalist.com/what-made-these-swirls-in-the-sand/. [Accessed: November 25, 2020]