Bristle Worms – A Complete Guide (Care, Diet, Facts)

Aquariums are a good way to keep pets in a confined space. With enough care, you can keep a variety of different fish and marine life in your home.

It’s difficult to imagine anything getting into your tank that you did not add to it. However, creatures like bristle worms make their way into fish tanks all the time. Bristle worms can keep your tank clean, but some varieties can harm you and your fish.

Bristle worms and whether you should keep them in your tank are controversial topics. Here is what you need to know about them so you can decide whether they should stay in your tank.


What Are Bristle Worms?

Bristle worms are part of the Polychaete class. All of the families and species in this class are segmented worms that live underwater. There are over 8,000 different bristle worm species.

These creatures are cylindrical and made up of different body segments. Every segment has parapodia, which is a pair of limbs that act like legs. The parapodia help active bristle worm species move around.

Bristle worms come in all sizes. They can be microscopic, and some species grow to be larger than 50 feet long. Bristle worms can also fluctuate in size and are difficult to measure.

Different bristle worm species can also have other identifying characteristics. For example, some varieties that live deep in the ocean can glow in the dark.

Bristle worms can also have different activity levels. There are two orders of species, sedentary and errant, that classify how bristle worms move and behave.

Sedentary bristle worms burrow into the ground or your tank’s substrate. They have a difficult time moving around their environment.

Errant bristle worms use their parapodia to move. They can swim and crawl around in your tank, and they get around easier than sedentary varieties.

Bristle worms are almost all detritivores that eat waste and anything else that reaches the bottom of your tank. Some of the more dangerous bristle worms are carnivores.

Most bristle worm varieties are from marine or brackish water. Only 2% of bristle fish varieties live in fresh water.

Bristle worms live in a wide range of different conditions. They can survive in very hot or very cold regions and at all ocean depths.

How Do Bristle Worms Get into Your Tank?

Fish keepers do not usually seek out bristle worms to add to a tank. Instead, bristle worms “hitch hike” their way into aquariums.

You may not even know if your tank has bristle worms inside. They are nocturnal and prefer to stay in the dark, so you would have to look for them at night using a flashlight.

The main way bristle worms get into aquariums is through live rock. Other natural decorations can bring bristle worms into your tank, but live rock is the main culprit.

Live rock is not actually alive. It is made of calcified skeletons from corals and other reef organisms that lived thousands of years ago.

Instead, live rock is named for the life that it often houses. Microorganisms and macroscopic marine organisms can live inside or outside live rock.

Aquariums use live rock to introduce healthy bacteria to act as a biological filter for the tank’s water. The life that these decorations hold can keep your water’s ammonia levels down because they turn ammonia into nitrates through the nitrogen cycle.

Bristle worms are one of the creatures that can inhabit live rock. You may think that only sedentary bristle worms live there because they are burrowers, but errant bristle worms also live in live rock.

When you add live rock to your tank, you risk bringing in all kinds of marine life without knowing it. Most of these organisms will benefit your tank, but some can harm it.

Using other natural decorations like driftwood can also introduce bristle worms to your tank. This is less common, but it’s certainly a regular occurrence.

You can prevent bristle worms from entering your tank’s ecosystem. The most common way to do this is to only use thermal-treated natural decorations.

Some natural decorations on the market have already been thermal treated. However, you can treat the decorations and live rock you buy at home.

Boiling the natural decorations you plan on using in your aquarium will get rid of any bristle worms living inside. This will also get rid of any healthy bacteria you may want to introduce to your tank.

Reasons to Keep Bristle Worms in Your Tank

Bristle worms can be good additions to your tank if you understand how to handle them. If you do your research and decide that the benefits are bigger than the risks, consider keeping the bristle worms that end up in your tank.

Bristle worms are detritivores, which means that they eat waste and other dead or rotting things in your tank. They will eat most things, which means that you rarely have to feed them yourself.

These detritivores are also creatures that can clean your tank. When they eat rotten food or dead animals, you do not have to go in and take them out.

Because bristle worms eat rotten food, they solve some of your tank’s problems. Rotten and dead things can create more algae in your tank. Bristle worms prevent algae from forming by getting rid of the things that encourage it.

The detritus and carrion that’s common in saltwater tanks can also cause an increase of ammonia, leading to higher nitrite and nitrate levels. By eating these, bristle worms also help to keep ammonia levels down.

One misconception about bristle worms is that they killed the fish you may find them eating. The truth is that they are almost always unable to harm the fish in your tank. They probably started eating the animal after it had already passed.

Harmful bristle worms are the exception rather than the rule. Some errant varieties are poisonous, carnivorous, or aggressive, but most bristle worms will not harm the other inhabitants of your tank. Be sure to identify what kind of bristle worm is in your tank.

Reasons to Remove Bristle Worms from Your Tank

Bristle worms can be helpful to keep in your tank, but they can also be annoying or even dangerous. They are difficult to handle, and some species are toxic.

A small reason fish keepers do not like bristle worms is simply because they aren’t pretty to look at. Some aquarists do not like the “ugly” or “creepy” appearance of bristle worms.

They also appear in tanks unexpectedly, which can startle or frustrate some fish keepers. A lot of planning goes into maintaining and balancing an aquarium, and a new arrival can throw off your tank’s ecosystem.

All bristle worms, no matter which species, can harm you if you aren’t careful. Their bristles are tiny spikes that look like hair, and bristle worms use them as a defense mechanism.

If you aren’t careful, these worms can get dozens of bristles stuck in your skin. Never touch or move a bristle worm without wearing gloves.

This risk is one reason some fish keepers decide to get rid of the bristle worms that appear in their tanks. However, this problem is less dangerous than some of the bristle worm varieties you might encounter.

Fire Worms vs. Other Bristle Worms

The main reason you would absolutely need to remove a bristle worm from your tank is if you had a fire worm on your hands. While most bristle worms cause no problems, fire worms can be harmful.

All bristle worms have bristles that can be annoying to remove, but fire worms have hollow bristles filled with toxins. They can cause you dizziness and nausea if they sting you, and they can kill your fish.

Some fire worms are also carnivorous in addition to being venomous. This means that they cause an even bigger threat to your fish.

Carnivorous fire worms will attack your fish. They will usually do this at night when most of the other fish in your tank are asleep.

Fire worms are less common than most other species of bristle worm. Of the 8,000 bristle worm species that exist, only about 120 of them are fire worms.

Just because fire worms are uncommon does not mean that you should assume the bristle worm you find isn’t a danger to your tank. Immediately identify any bristle worm you find in your aquarium to make sure it isn’t a fire worm.

Fortunately, fire worms are easy to recognize. They are larger than other bristle worms, and their bases are a brighter color than other bristle worm species.

Fire worms also have well-defined bristles. Their chaetae also have a reddish color at the base where the toxins are stored.

How to Remove Bristle Worms from Your Tank

If you decide to remove the bristle worms living in your tank, you have a few options. You can add natural predators to your tank to eat them, or you can set bristle worm traps.

Keeping natural predators is a good idea for any tank. These creatures will control population levels for a variety of organisms, not just brine worms.

Arrow crabs, coral banded shrimp, and a few different wrasse species are common predator choices. They will not attack your tank’s fish, and they are creatures besides fish that will add some variety to your tank.

Some fish are also bristle worm predators. Pufferfish and butterflyfish will also eat bristle worms, but not all types will.

When researching natural predators to add to your tank, make sure they are compatible with your tank’s habitat. All of the predators listed are reef safe, but not all natural predators are.

You can also set traps to catch and remove bristle worms. This method is a good option if you do not already have natural predators in your tank or if you need to remove the bristle worms quickly.

There are commercially available bristle worm traps. They are inexpensive, but they may not be readily available.

You can also make your own bristle worm trap by using a plastic bottle. Cut it in half horizontally and flip the top half upside down and glue it to the top of the base.

When you bury this trap in your substrate with the hole facing up, bristle worms will fall into the bottle and be unable to climb out.

If you only have a small number of bristle worms to remove, you can also remove them individually with tweezers. You will need to be careful not to let the bristles sting you if you use this method.

Fire worms are the most important bristle worm to remove quickly, but they are also difficult to catch. Consider placing several traps in your tank to capture them faster.

How to Safely Handle Bristle Worms

As mentioned earlier, all bristle worms have bristles that will sting you if you aren’t careful. Once you’ve trapped your bristle worms, you need to handle them without hurting yourself.

The most important rule when handling bristle worms is to wear gloves. This will protect your hands from the bristles and prevent any stings, poisonous or not.

Gloves are especially important if you are removing bristle worms by hand. Tweezers help with this process, but you must wear gloves if you use this method.

You can do several things with bristle worms once you’ve caught them. If you only needed to remove them from your tank, you can keep them in a separate tank. They will need to be kept in similar conditions as the tank they were found in.

Keeping the bristle worms you remove from your tank may not be the best idea. Maintaining a second tank is a lot of work, and they would need to be fed regularly.

Consider taking the bristle worms you trap to a pet store. They will be able to relocate them or dispose of them if you’re unable to.

If you have no other options, putting the bristle worms down yourself is a possibility. This should only be done as a last resort.


Bristle worms are a controversial subject in the fish keeping community. Good bristle worms can clean your tank by eating algae and dead or rotten food. On the other hand, fire worms and other harmful varieties can harm you and the fish in your tank.

You do not need to take bristle worms out of your aquarium unless they are fire worms. When you handle the bristle worms, be sure to wear gloves and be careful to avoid hurting yourself.

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