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Home › Sea Life › Marine › Invertebrates › Annelids › Bloodworms

Interesting Facts about Bloodworms

[Bloodworm Phylum: Annelida] [Order: Phyllodocida] [Family: Glyceridae (polychaete worms)]

Marine bloodworms, from the genus Glycera, are bright red or pink coloured polychaete annelid worms that thrive in low-oxygen environments.

Unlike earthworms (which live in soil), sea worms are aquatic bristle worms that live in muddy sediment. They are an important source of food for most bottom-feeding fish families and some saltwater crustaceans.

Marine Bloodworm Habitats and Distribution

Glycera annelids (polychaete worms) inhabit almost all of the shallow marine environments worldwide.

But, the global range tends to be concentrated in select temperate and tropical coastal marine environments, such as:

• North Atlantic Ocean (especially Canada, Europe, and eastern U.S.)
• Indian Ocean
• Pacific Ocean (e.g. Asia, the West Coast of North America)
• The Mediterranean Sea

There are about eighty (80) different species of Glycera (family Glyceridae) and most of these segmented worms live in the continental shelf zones.

Despite the preference for living in intertidal zone habitats, it is not uncommon to find some species surviving at depths approaching one hundred (100) metres (330 feet).

Still, almost all marine bloodworms need a sand or mud substrate so they can burrow inside to seek shelter. Thus, you'll most likely find annelida species living at coastal seafloors, estuaries, mudflats, and salt marshes.

Marine Bloodworm Characteristics

The head of a sea worm has four (4) small antennae that contain parapodia (small fleshy projections). Moreover, the teeth and jaws of these unique invertebrate sea animals contain about 10% copper halide mineral (atacamite to be more specific).

Even though the copper content is not actually poisonous to the worm itself, marine bloodworms use their tough copper-infused teeth as a venomous defencive system and a hardened mechanism to bite their preferred prey.

Why are Marine Bloodworms Red Colour?

The bright red pigmentation in bloodworms (Glycera) comes from an adaptation to low-oxygen (hypoxic) environments.

Put another way:

Their body fluids contain a protein called 'haemoglobin', which is why they appear as creamy pinky or red coloured worms.

After reaching full maturity, some of the common bloodworms can grow up to thirty five (35) centimetres long (14 inches).

What Do Marine Bloodworms Eat?

In fact, bloodworms in the sea are predatory carnivorous animals that feed by extending an elongated appendage (e.g. a retractable proboscis) that opens up as four hollow jaws.

Besides scavenging in nutrient-rich mudflats for detritus (dead or decaying organic matter), the typical daily diet for these nocturnal sea worms includes tiny benthic invertebrates, such as:

• Crustaceans (e.g. amphipods, copepods)
• Larvae of mollusks and fish
• Polychaetes (including other smaller segmented worms)

Pro Tip: The jaws connect to internal glands that supply the venom used to kill their prey (e.g. neurotoxins and proteolytic enzymes). However, even though the bite of a bloodworm would be painful for a human, it is unlikely to be fatal.

Glycera Bloodworm Species List

How Do Bloodworms Reproduce?

The Glycera reproductive process usually takes place when the water temperature gets warmer in the midsummer months.

The lunar cycle, and tidal patterns, can also trigger sexually mature male and female worms to transform into the epitoke stage (a non-feeding cycle).

Here's the thing:

This spawning process and external fertilisation begins with enlarged parapodia. Members from both sexes migrate to the surface of the water to release their gametes (eggs and sperm). Following which, the adults will die.

After the fertilized eggs develop into planktonic trochophore larvae, a common larval stage in annelid worms, the larvae drift in the water column with plankton before they eventually settle on the ocean floor and start to grow.

Threats and Predators

The average lifespan for marine bloodworms (Glycera) is around two (2) years - slightly longer in some species.

Despite their burrowing lifestyle and venomous bite, ocean worms face a variety of natural threats and predators, especially demersal marine life during low tides. Typical examples include:

• Bottom-feeders (e.g. Atlantic croaker (Micropogonias undulatus), cod, flounders, wrasses)
• Crustacea (e.g. crabs, shrimp)
• Other larger polychaetes
• Shorebirds (e.g. sandpipers, plovers, and gulls)

Bloodworms are biologically-distinct from sandworms (e.g. lugworms) even though they share similar features and are both used as fishing bait.

For example, Glycera bloodworms are sold commercially in tackle shops. Fisherfolk use them as a luring substance and as bait to catch big fish.

Pro Tip: Another section contains a detailed list of recommended aquarium fish food brands, including bloodworm fish food. Choosing the best food for your fish is key for maintaining a healthy aquarium.

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