Bristle Worms: Do They Eat Hermit Crabs? Are They Harmful or Beneficial?

Have you ever wondered what bristle worms do and whether they are a cause for concern? As a saltwater tank owner, you might sooner or later see one of these segmented worms come out from underneath a rock, and then it is normal to have questions.

Perhaps you are wondering if your new hermit crabs will be eaten by the bristle worms, or if they will harm your Duncan coral

The good news is that bristle worms tend to be harmless, and in fact, beneficial for a reef tank, as they take on a cleaner role and feed off dead tissue, animals, and organisms.

Recognizing Bristle Worms

Bristle worms are large and sometimes easy to spot, and they can grow to become as big as 24 inches long, even though most are only about 1-6 inches long. They are segmented and have long extended tufts sticking out of the segments.

While the bigger ones aren’t too hard to see, you can have bristle worms in your tank without realizing, as they can also be great at hiding in live rock and hollow spaces.

You want to avoid ever touching a bristle worm with your bare hands, as they have bristles that can be compared to a cactus! What do cactus bristles do? They stick to your skin and can cause irritation and itching, just like bristle worm bristles.

How Bristle Worms Benefit the Tank?

When hearing the name “bristle worm,” our instincts tell us that we don’t want them in our tanks and that they need to be removed. However, bristle worms can actually be beneficial!

These worms are scavengers that search the tank for food, and they tend to eat carrion or food left behind by other tank organisms, and they also eat detritus.

In many ways, you could say that these worms have the jobs of tank cleaners, and their “work” helps remove dead tissue and animals that would have otherwise caused the release of ammonia when decomposing – putting unnecessary stress on biological tank filters.

Bristle worms are excellent helpers when it comes to keeping a saltwater tank clean. It is important to note that not all types of bristle worms are beneficial for the tank, and it is crucial to determine what type you are dealing with before proceeding.

How About Downsides, Do They eat hermit crabs?

Do bristle worms eat hermit crabs? How about other animals? Can it hurt your corals? These are some of the questions many tank owners have when first discovering that there are bristle worms in the tank. 

Some argue to have seen these worms eat other living things in the aquarium tank, but it is not a species that is known for being aggressive, and they are therefore unlikely to be the culprit when you find a dead fish or crab at the tank bottom. 

Instead, the most likely explanation is that the bristle worm was scavenging as bristle worms do and that if found a dead or dying meal ready to be eaten. They will, indeed, eat both hermit crabs, shrimp, and fish, but are not likely to kill living and healthy animals, which would mean that they don’t present a risk to them unless they are already dead.

How to Get Rid of Them?

If you opt for getting rid of the bristle worms in your reef tank, it is safe to say that you are not up for an easy task. It can be both challenging and surprisingly time-consuming to get rid of bristle worms, and many opt for using predators to eliminate them in a more natural way.

Be aware that predators can be unpredictable though, and while they will eat and remove the bristle worm problem from your tank, they may also go after crustaceans and some other inverts, which could cause havoc in your idyllic saltwater tank. 

The best way to avoid problems is to allow the predators to successfully consume the bristle worms and to proceed to remove them from the tank once they are done.

Be Aware of Hidden Bristle Worms

There is only so much a natural predator can do, and they can’t hunt and eat bristle worms they can’t see. Some worms may be hiding in cracks and openings of the rocks in your tank, and there you have to step in and be a little more hands-on. 

Lift out rocks with big cracks where you think bristle worms could be hiding, and gently dip them into dechlorinated freshwater to encourage the worms to come out of their hiding place. You might have to use tongs or a pair of tweezers to remove some manually as well.

Examples of Predators to Eliminate Bristle Worms

Choose your predators wisely and read up on each species so that you know what to expect, and be aware of the fact that you are likely going to have to consider removing them again later, or make sure there is no other organism that could be harmed or eaten (unless, of course, that is your intention).

  • Maori Wrasse (Cheilinus oxycephalus)
  • Arrow Crab (Stenorhynchus setrcornis) 
  • Bird Wrasse (Gomphosus varius)
  • Coral Banded Shrimp (Stenopus hispidus)
  • Sunset Wrasse (Thalassoma lutescens)

Depending on how sensitive your tank organisms are, you might need to quarantine your predators before letting them into your main tank. Consider the benefits of having bristle worms in the tank before you decide to eliminate them.


Bristle worms can appear in your saltwater tank and are not considered to be a cause of concern, as they are not dangerous and don’t tend to disturb the tank life. These worms should not be confused with the much more aggressive fireworm.

While you may catch a bristle worm eating a hermit crab, fish, or other animals, it is highly unlikely that the bristle worm killed it, and the most likely explanation is that the worm found an organism that was already dead and decided to eat it.

Having bristle worms in the tank can sound unpleasant, but they are small scavengers that aid in keeping the tank clean and free from, for example, ammonia.


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