Bearded fireworm | What’s that marine bug?!

Wondering what that bug was you came across while snorkeling or diving? In “What’s That Marine Bug?!” we have a look of some of the weird and wacky invertebrates that can be found in oceans and seas. Today: the bearded fireworm (Hermodice carunculata), which falls firmly into the ‘look-but-don’t-touch’ category.

Bearded fireworm appearance

As far as worms go, the bearded fireworm is definitely not one of the ugliest ones. In fact, they’re quite frilly! The species is a member of the bristleworm family (Amphinomidae), which get their common name from their chaeta, or bristles. The bearded fireworm sports a dark, segmented body with white ridges. On the side of each of its segments is a reddish-orange gill structure and a cluster of fuzzy-looking white chaeta.

Do NOT touch these worms, even if they do look fluffy. There is a reason these guys are called fireworms, and it’s not their color. Rather, it’s the neurotoxin contained in the hollow bristles, which won’t kill you but can very intensely irritate the skin and cause severe nausea.

Bearded fireworms can grow to up to 30 centimeters in total length.

Name (common, scientific)Bearded fireworm, Hermodice carunculata
FamilyAmphinomidae
SpreadTropical Atlantic Ocean, Mediterranean sea
HabitatNot fussy; up to 40m deep.

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Bearded fireworm habitat

The bearded fireworm can be found throughout the warmer areas of the Atlantic, including the Caribbean and the Gulf of Mexico. It’s also common in the Mediterranean Sea and the Red Sea. In fact, some studies suggest it’s spreading in the Mediterranean, likely due to the water warming as a result of climate change.

This increasing spread can have some significant downsides, given the fact that the worms like munching on corals. They can also carry certain coral diseases, including dormant coral-bleaching bacteria that can jump from coral to worm to coral. All of this isn’t normally much of a problem, but it can become one when coral colonies are already threatened. The worms are also a potential nuisance to swimmers and fishermen.

This species doesn’t have much of a specific habitat preference, popping up pretty much everywhere up to 40 meters in depth. Not surprising given its omnivorous nature, unfussiness about environmental conditions and bristled defense system: it can thrive wherever as long as the waters aren’t too chilly. You won’t usually see them during the day, though, as they’re nocturnal.

I photographed this bearded fireworm in a tide pool in Gran Canaria, Canary Islands.

Bearded fireworm in the aquarium

If you’re a marine aquarium enthusiast, you may already have heard of the bearded fireworm before you stumbled upon this article. These worms are aquarium “hitchhikers”, a name for bugs that make their way into saltwater tanks by hitching a ride on live rock bought at pet stores or from fellow aquarists. Fireworms can occur on Caribbean live rock. It’s not hugely common – most worms that pop up are harmless bristleworms – but it can happen.

Some hitchhikers are harmless, but it’s not difficult to imagine that a bearded fireworm in your tank can be problematic. If you keep corals, they may be eaten, not to mention the effect if you accidentally touch the fireworm!

To remove a bearded fireworm from your tank, keep some long tongs handy in case it comes out and you can grab it. If you don’t think you’ll get the chance to do that, you can set up a homemade trap. Some aquarists also utilize “biocontrol” in the form of creatures that naturally eat fireworms, but there aren’t that many out there. Cone snails are one of the bearded fireworm’s natural predators, but those are actually way more venomous than the worms themselves. Certain species of wrasses might be interested.

Bearded fireworm facts

  • Diet: Bearded fireworms are omnivores with a preference for scavenging. That being said, they have absolutely no problem switching to predator mode either, happily munching away on all sorts of invertebrates.

    Corals and anemones are a notable food source, but the worms will also eat sea urchins, nudibranchs, molluscs, sponges and much more. If they need a little greenery, they go for macroalgae or sift through detritus.
  • Toxin: A bearded fireworm that’s attacking or under attack will raise its bristles, which are thought to be able to inject or brush a mixture of toxins into the skin. Scientists are still a little unclear on how they produce these toxins. To us snorkel enthusiasts, it’s probably enough to know that they can cause strong inflammation, intense pain and itching, nausea and sometimes even infection.

    If you’ve been stung, try using adhesive tape to remove any bristles stuck in your skin. After that, the application of hot water, vinegar or isopropanol may help.
  • Biofluorescence: Yep, these worms fluoresce. They’re nocturnal, and at night, they produce a green glow! It’s not entirely clear why, but it may have something to do with mating rituals or defense.
  • Life cycle: According to a 2020 study, bearded fireworms mate by releasing eggs and sperm while swaying back and forth. After hatching, the fry go through a larval stage. They float around the water column until they metamorphose into adults.
  • Regenerative abilities: Like many other worm species, bearded fireworms can survive being chopped in half. In fact, both halves will re-grow to produce a complete worm. As if those bristles weren’t enough of a protective measure!

Any more questions about the bearded fireworm or want to share a story of one of your own encounters with these deceptively pretty worms? Feel free to leave a comment below.

Sources/further reading

Ahrens, J. B., Kudenov, J. D., Marshall, C. D., & Schulze, A. (2014). Regeneration of posterior segments and terminal structures in the bearded fireworm, Hermodice carunculata (Annelida: Amphinomidae). Journal of Morphology275(10), 1103-1112.

Righi, S., Prevedelli, D., & Simonini, R. (2020). Ecology, distribution and expansion of a Mediterranean native invader, the fireworm Hermodice carunculata (Annelida). Mediterranean Marine Science21(3), 558-574.

Schulze, A., Grimes, C. J., & Rudek, T. E. (2017). Tough, armed and omnivorous: Hermodice carunculata (Annelida: Amphinomidae) is prepared for ecological challenges. Journal of the Marine Biological Association of the United Kingdom97(5), 1075-1080.

Simonini, R., Maletti, I., Righi, S., Fai, S., & Prevedelli, D. (2018). Laboratory observations on predator–prey interactions between the bearded fireworm (Hermodice carunculata) and Mediterranean benthic invertebrates. Marine and freshwater behaviour and physiology51(3), 145-158.

Toso, A., Boulamail, S., Lago, N., Pierri, C., Piraino, S., & Giangrande, A. (2020). First description of early developmental stages of the native invasive fireworm Hermodice carunculata (Annelida, Amphinomidae): a cue to the warming of the Mediterranean Sea. Mediterranean Marine Science21(2), 442-447.

Verdes, A., Simpson, D., & Holford, M. (2018). Are fireworms venomous? Evidence for the convergent evolution of toxin homologs in three species of fireworms (Annelida, Amphinomidae). Genome biology and evolution10(1), 249-268.

Witman, J. D. (1988). Effects of predation by the fireworm Hermodice carunculata on milleporid hydrocorals. Bulletin of Marine Science42(3), 446-458.

Wolf, A. T., Nugues, M. M., & Wild, C. (2014). Distribution, food preference, and trophic position of the corallivorous fireworm Hermodice carunculata in a Caribbean coral reef. Coral Reefs33(4), 1153-1163.