Polychaeta is a class of segmented worms covered in tufts of chitinous hair. This giant group of more than 10,000 species of worms are collectively known as the bristle worms. Bristle worms are robust and can tolerate a range of conditions, but are more generally found in saltwater environments. Less than 2% of all polychaetes are found in fresh waters. Bristle worms will typically enter your reef burrowed deep in the live rocks. They’re excellent hiders and will usually only come out at night to feed. Bristle worms can be pretty small, but some of the species that we see in reef keeping can grow up to 12 inches long. If you find a bristle worm has hitched a ride into your tank, there’s no need to panic. You just have to weigh the risks versus the rewards of keeping this new guest. There is debate in the reef keeping community on whether bristle worms are beneficial in a reef tank or if they should be removed immediately. I hope this guide can help you make the best choice for your tank.
The rewards? Bristle worms can make a great addition to your clean up crew. Being mainly detritivores, they will eat most of the stuff in your tank that you want gone like dead/dying livestock, uneaten food, etc. Being nocturnal, bristle worms usually won’t make an appearance during the day unless they are starving. At night, they will come out and go to work sifting through the sand. Being able to squeeze into tight crevices, they can clean the spots that your typical clean up crew can’t reach.
The risks? Some bristle worms are fire worms, but not all fire worms are bristle worms. Confused? Yes. Let me explain. Certain species of bristle worms are considered to be “fire worms.” Fire worms are the less common species of bristle worms that have neurotoxin in the chitinous hairs that cover their bodies. Bristle worms can shed their hairs when they are touched. It’s uncomfortable to have those hairs embedded in your skin, but they can usually be removed easily with tweezers. However, the embedding of the hairs from a fire worm are more painful and burns even after removal. A fire worm brushing up against a sleeping or sick fish could have bad consequences. Also important to note, some species of fire worms are not reef safe at all. The bearded fire worm will eat corals, anemones, and small crustaceans.
If you decide on removing a bristle worm, don’t go in without wearing some gloves. It may be best to remove its home rock and try to pull the bristle worm out with tweezers. Dunking a whole live rock into a bucket of fresh water can sometimes make the bristle worm(s) come out. If removing your rock work isn’t an option, there are a variety of “worm traps” online that you could try. The idea is that the bristle worms will enter the trap at night when they are feeding and they all get stuck inside the trap. There are also creatures that eat bristle worms like some species of wrasses. While a Fairy wrasse won’t, a Melanurus or a Six-line wrasse will. Arrow crabs, coral banded shrimp, and peppermint shrimp will also eat bristle worms.