Eyes Under Puget Sound: Critter of the Month—Bloodworms

Left: Dany identifies marine critters at the South Sound BioBlitz on August 11, 2018.

Center: Glycera americana, a species found on both the east and west coasts, has finger-like gills that shoot out from behind its feet.

Right: Our 2016–2017 WCC intern, Nicole Marks, holds a Glycera robusta specimen freshly collected from a benthic grab sample.

It’s a Bioblitz!

Recently I had the pleasure of volunteering at the South Sound BioBlitz, a community outreach event hosted by the Pacific Shellfish Institute. Participants spent a rainy Saturday morning working with local scientists conducting beach surveys to find intertidal invertebrates. Most species were catalogued in the field, but some specimens were brought back to the WET Science Center for closer examination. It was a great way for folks of all ages to get up close and personal with Puget Sound’s benthic (sediment-dwelling) invertebrates!

One of the most common finds at our survey location was a small, pink, wiggly worm with a pointy head. I immediately recognized it as a bloodworm because of its paper thin skin that reveals its red body fluid inside.

Bloodworms are a type of polychaete, or marine segmented worm, in the family Glyceridae. The intertidal species are only a couple of centimeters long, but we get a much larger version in our Puget Sound subtidal benthic grabs that can be over a foot long (see video below for one of these big beauties)!

In cold blood

I often get the question, “Do bloodworms bite?” Well, yes and no. The bloodworm is a voracious predator and has a long proboscis, or mouthpart, that can shoot out of its body like something in a horror movie. At the end are four black jaws that are connected to venom glands. Despite their sinister name, bloodworms typically save their venom for the tiny crustaceans they like to eat. They don’t usually harm humans intentionally, but if you did happen to put your finger near the worm’s mouth, you could end up with a minor bee-sting-like bite.

The bloodworm’s black jaws are especially strong because they contain a copper-based mineral that makes them almost as hard as human tooth enamel—an important quality when you are munching on sand grains with your food!

Blood in the water…and in the mud

When you take a bloodworm out of its habitat, it will thrash around like a fish out of water (see video below—watch for the proboscis shooting out). This makes them great for attracting actual fish, which is why fisherman commonly use them as bait. Don’t confuse them with the popular aquarium fish food; those small red freshwater bloodworms are actually midge fly larvae.

In addition to their usefulness to humans, bloodworms provide an important ecological service. They are highly mobile, burrowing into the sand or mud with their pointed snouts. This activity is called bioturbation, or mixing of the sediments, and it allows much needed oxygen and nutrients to penetrate into the deeper layers of sediment. The burrows made by the worms can also provide habitat for smaller critters, helping drive biodiversity. Bloodworms may not be beautiful, but Puget Sound sediments would certainly be a less productive and interesting place without them!  

By: Dany Burgess, Environmental Assessment Program

Our benthic taxonomists, Dany and Angela, are scientists who identify and count the benthic (sediment-dwelling) organisms in our samples as part of our Marine Sediment Monitoring Program. We are tracking the numbers and types of species we see in order to understand the health of Puget Sound and to detect any changes over time.

Dany and Angela share their discoveries by bringing us a Benthic Critter of the Month. These posts will give you a peek into the life of Puget Sound’s least-known inhabitants. We’ll share details on identification, habitat, life history, and the role each critter plays in the sediment community. Can't get enough benthos? See photos from our Eyes Under Puget Sound collection on Flickr.