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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.

Blood Worm 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 blood worms 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 Red Aquatic Worms 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. Hence the common name of beak-thrower worms.

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

Glycera alba

Glycera alba is one of the marine polychaete worms that belong in the family Glyceridae, commonly called bloodworms. They typically grow to seven (7) centimetres in total body length - made up with about 150 ringed body segments.

The body colour is milky white (paler than most bloodworm species with hemoglobin-rich body fluids) and the general shape is elongated and cylindrical, with distinct narrowing at both ends.

There are small antennae and palps arranged in a cross-like pattern located at the tip of the conical shaped head (called the prostomium).

They also have pairs of parapodia (fleshy paddle-like appendages) on each segment bearing bristles (called setae), that become biramous appendages from the mid-body section (dividing to form two branches).

Diet and Feeding Habits

Like most types of blood worms, Glycera alba also has a reversible proboscis that is equipped with four (4) chitinous jaws. They connect to the venom glands and the worm uses them to capture their favourite prey - tiny marine invertebrates (especially crustaceans and other polychaetes).

The venomous proteinaceous toxins, secreted by the jaws and associated glands, enable the immobilisation and pre-digestion of prey. Scientists believe that these bioactive compounds (including glycerotoxins) have a significant impact on neuromuscular systems.

Habitat and Distribution

Glycera alba are known to inhabit marine benthic environments, especially the ones with muddy and sandy substrates, and most often at depths ranging between ten (10) and three hundred (300) metres (984 feet).

These burrowing predators are most common in the Northern Atlantic, parts of the Mediterranean Sea, and other marine regions with temperate water.

Glycera americana

Glycera branchiopoda

Glycera capitata

Glycera convoluta

Glycera dibranchiata

Glycera gigantea

Glycera juliae

Glycera longipinnis

Glycera nana

Glycera nicobarica

Glycera oxycephala

Glycera papillosa

Glycera robusta

Glycera rouxi

Glycera sheikhmujibi

Glycera tasselata

Glycera tridactyla

Glycera unicornis

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 blood worms (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.