Should You Keep a Bristle Worm in Your Aquarium?

The bristle worm, also known as the Polychaeta, is one of the most controversial critters in the saltwater aquaria hobby.

Some reef keepers are adamant that they should be avoided at all costs, while others suggest that they can be beneficial to the health of a saltwater setup.

So, should they stay or should they go? In this guide, we look at the pros and cons of leaving bristle worms in your aquarium.

Common NameBristle Worm
Scientific NamePolychaete
SizeUsually 1″ – 6″, but can grow up to two feet
DietMostly algae, uneaten fish food, and waste
ColorPink or gray in color

What is a Bristle Worm?

The term “bristle worm” refers to several thousand different worms, each with separate behaviors and anatomy. They are a type of segmented worm and generally present with bristles along their sides, many of which are toxic and poisonous.

This presents a major problem for both you and some of your inhabitants, because if you happen to brush against a rock hiding a bristle worm, you will end up with these bristles in your hand or arm.

As you may imagine, this is an issue for both you and other inhabitants of your tank.

However, most bristle worms are peaceful and generally non-harmful, unless a fish runs into them or is overly curious.

Even then, fish normally survive a few bristles.

In addition, bristle worms are not capable of shooting thier bristles at fish or using them aggressively; they only come off once something touches them.

Most of them are either detritivores or omnivorous, eating the stuff that nothing else in the tank will eat.

They will take care of food other fish and invertebrates missed, carcasses, and reprocess the waste of other creatures. In this manner, they can be helpful in the tank, similar to detritus worms in freshwater tanks.

Unlike detritus worms, there are some unpleasant species you may encounter.

While the vast majority of bristle worms are harmless, there are some that can be dangerous, both to your fish and to you.

The fireworm is the most commonly encountered one; its bristles are much more potent than other bristle worms, and it frequently snacks on invertebrates, coral, and small fish.

The bobbit worm is likely the worst one you can encounter.

It hides beneath the sand and strikes upwards when fish or other creatures are above, and its jaws are capable of slicing a fish in two.

If you’re not careful, it can cause some serious damage to your arm or hand.


Benefits of Keeping a Bristle Worm in Your Aquarium

As previously mentioned, these worms will eat various types of decaying matter, which can be incredibly helpful.

Most of the time you won’t realize that you have bristle worms, as they often come out at night to clean up the tank of anything the other inhabitants missed.

If you suddenly remove one, you’ll start seeing more decaying matter than you previously did, which can, in some cases, cause an ammonia and nitrite spike, which is awfully harmful.

While it will likely just result in some extra daily or weekly maintenance for you, plus a feeding adjustment, it may be worthwhile to simply leave the worm where it is.

There is a low chance of a harmless bristle worm reproducing by feeding on just leftover matter, so it is unlikely that they will overrun your tank.

In addition, as previously mentioned, they will feed on dead fish carcasses. As you know, a decaying fish will quickly raise your ammonia to unsafe levels, and if you can’t find the body fast enough, it can crash your tank.

Even just one bristle worm will be able to help you cut down on the amount of ammonia, or even find the body.

If you don’t have a dedicated CUC (clean-up crew) a bristle worm can be your entire crew if you leave it in the tank.


Negatives of Keeping Bristle Worms in Your Aquarium

While they can be beneficial by ridding your tank of decaying matter, they do pose some danger.

As previously mentioned, even the peaceful ones can have toxic bristles. Luckily, they only cause mild irritation, but it is up to you whether or not keeping that risk around is worth it.

Simply moving some rocks can result in painful bristles ending up in your skin.

While this is not a common occurrence, as most peaceful bristle worms are well hidden in rocks, it is a possibility to be aware of.

Aside from possible mild irritation of the epidermis, normal bristle worms will leave your flora, fauna, coral, and fish alone and will not cause harm to the tank.

On the other hand, fireworms and bobbit worms are harmful to your fauna, and will be discussed in more detail below.

Grubs and Worms

One of the primary reasons that bristle worms have such a bad connotation is not due to their toxic bristles, but rather to a common misunderstanding.

Back when people were first keeping marine fish, there were bristle worms carried along with the live rock.

Most of the time, people weren’t aware that they had bristle worms and would only see them after a fish died, with a worm feasting on the body.

This led many to conclude that the worms killed the fish, when poor husbandry was a more likely culprit.

Think of these worms like maggots and grubs (but better, and less gross looking).

If you happen upon a dead deer carcass and see maggots feeding on the body, you’re not going to assume that the maggots killed the deer.

Likewise, a worm feeding on a dead fish doesn’t mean it killed the fish; it’s likely just cleaning up the tank.


Bristle Worm Lookalikes to Look Out For

Part of the reason why the bristle worm has such a bad reputation is because they’re often confused for other (more dangerous) types of marine worms.

Here are a few that you should look out for:

Fireworms­

Unlike most other bristle worms, these worms are carnivorous.

They will still feed on decaying matter left in the tank, but they will also feed on living invertebrates, including coral, and vertebrates, such as your fish.

In addition, their bristles are much more dangerous and painful, and can even result in an emergency room visit.

While most bristle worms only cause mild irritation with their bristles, fireworm bristles are very toxic.

If you brush up against one, you will be in a lot of pain. Do not remove the bristles and refer to the below section on how to treat the stings.

As you may imagine, if they can cause severe pain to a large human, they can easily take down fish with the same amount of toxins.

In addition to this, fireworms are capable of rapid reproduction, unlike other bristle worms, and run the risk of taking over your tank.

Their food source is not limited to decaying matter left behind by other tank inhabitants, meaning they have a much larger variety and amount of food. This leads to rapid reproduction, and the rapid demise of other tank inhabitants.

It is easy to identify a fireworm if you have seen a normal bristle worm, as you have to compare the two to identity the fireworm.

If you have only pictures, it can still be done, but is a bit trickier.

Fireworms normally have bristles with a red base, red, green, yellow or brown external gills, and white tipped bristles. These can of course range a good bit, as there are several species of fireworms.

In addition, if you happen to see some type of bristle worm wandering around in the middle of the day, it’s likely a fireworm.

Other bristle worms are very timid and prefer to come out to scavenge at night, but fireworms will come out during normal feeding times to look for any possible food.

It is best to remove these as soon as you see them, as they are a threat to nearly everything in your tank and present very few, if any, benefits.

Bobbit Worms

Bobbit worms, while rare, are some of the worst possible things you can discover in your tank. They are highly aggressive and dangerous, and do not act like any other bristle worms.

While most other bristle worms spend most of their time hiding in rocks, only coming out at night to scavenge, bobbit worms are aggressive ambush predators.

They bury themselves in the sand, with only their large jaws and mouths sticking out.

When a fish passes above them, they rapidly shoot out of the sand, grab the fish with their jaws, and pull them under the sand. They strike fast and hard, capable of moving at 20 feet per second and slicing fish in half.

If you see any sort of worm sticking out of your substrate, you need to move it immediately.

However, you must be extremely careful. Remember that they can slice a fish in half, so they can also do some serious damage to your hand and arm.

This is the only bristle worm where the actual bristles are not the issue.

They are powerful and can grow well over ten feet in length in proper conditions. If they are left in the tank, your fish and invertebrates will be killed and consumed by this creature.


Bristle Worm Sting Treatment

When you get stung by a bristle worm or fireworm, you will not have trouble finding the affected area; it will hurt, and you will know exactly where you were stung.

The bristles will remain in the skin, so be careful not to touch other flesh or drive them in deeper.

Start by applying vinegar to the affected area.

Carefully remove the bristles with either tweezers or tape. There will be somewhere between several dozen to several hundred bristles, and you must remove them all to alleviate the pain.

After you have removed all the bristles, apply hydrocortisone ointment to the affected area, and take over the counter pain killers, especially if you were stung by a fireworm.

Do not be afraid to go to your doctor to treat this wound if need be.

The bristles of a bristle worm are hollow, which means there is a good possibility that bacteria from your tank are in them.

While most of these bacteria cannot survive out of the aquarium, it is possible that some of them will cause the wound to become infected.

If the redness or swelling persists for more than a few days, or pus appears, you should schedule a visit with your doctor immediately.


How to Remove Bristle Worms from Your Aquarium

If you find a bristle worm don’t need it, or you find a fireworm and need to get it out as soon as possible, there are several methods you can use.

Manual Removal

The first, and one of the easiest methods, is to manually remove any of the worms you see. While you can do this with tweezers, it is often easier to target the rock that the worm is hiding in.

Once you know which rock the worm is in, lift the rock out of the water and dip it into a bucket of dechlorinated tap water.

This will shock the worms and cause them to fall to the bottom of the bucket, though a few tricky ones may still need to be removed with long tweezers.

However, only experienced aquarists should attempt a freshwater dip.

If you are not experienced in this area, there is a good chance that you will do much more harm than good. In this case, it is best to wait until you see the worm, then grab it with tweezers.

When it comes to disposing of the worm, surprisingly, a good number of people are actually in search of some bristle worms.

You may be able to ship it to someone searching for one, and even make a small profit off of the worm.

The same can be done for bobbit worms, as a few wish to have tanks dedicated to this predator, but almost no one is searching for fireworms.

Traps

While there are many types of worm traps available on the market, even specialized ones for Bobbit worms, you can easily make your own worm trap.

You will need empty soda bottles and straws.

You can make a trap with just a soda bottle, or one with a soda bottle and straws. Both seem to work, so there doesn’t seem to be much difference between them. You need to place some kind of food into the bottles to draw the worms in.

For the soda bottle one, simply cut off the top of the soda bottle and invert it, so that the part you drink from is now inside the bottle.

The worms will crawl up the sloped side and drop into the bottle, but because the entrance is above them, they will no longer be able to get out.

For the trap with straws, you can set the bottle either upright or lengthwise.

If you place it upright, drill holes along the bottom, but at least ¾-1” above the bottom of the bottle. If you place it lengthwise, make sure the holes are ¾-1” higher than the ground will be when you place it down.

Drill several holes, two or more, into the sides of the bottle. The straws will go into these holes, so it is best to make the holes slightly smaller than the straws to ensure a secure fit.

Similar to the previous trap, the worms will crawl into the straws and land in the bottle but will be unable to get out.

Predator Introduction

This method should be regarded as a last resort. If you have either a fireworm or bristle worm infestation, and the other methods failed or are making no impact, this may be your solution.

There are many types of fish that find these worms tasty, but there is a good chance that they will find other invertebrates in your tank tasty as well.

If you happen to have a tank without other invertebrates or small fish, you may be able to find a predator that will fit your tank.

Understand that once you add a new fish, you may have to tear down your tank in order to get it out. Be sure that the fish you pick can be a permanent member of your aquarium.

Some of the more popular choices of predators for these worms are arrow crabs, triggerfish, the sunset wrasse, and the dottyback.

While these fish can fit in many aquariums, you must ensure that they will work with every single member of your aquarium, or you will have a disaster.


How to Prevent Bristle Worms from Getting in Your Aquarium

The easiest method of “removal” is to prevent them from ever getting into your aquarium in the first place. All these worms, the normal bristle, fireworms, and even bobbit worms, will hitchhike in on live rock.

Live rock is essential for all saltwater aquariums, but not all of these rocks are entirely safe for your aquarium, purely due to the hitchhikers.

The best way to prevent anything unwanted from getting into your aquarium is to quarantine everything you bring in.

Most of the time, this refers to quarantining fish and invertebrates to prevent the possible spread of diseases, but for saltwater aquariums, this should also apply to the live rock, and live sand if you are so inclined.

There have been a few reports of people getting Bobbit worms in their sand, but the sand was also added at the same time as live rock.

It is much more likely that these worms are hitchhiking in on the rocks, and not inside of the sand. It is unlikely that you will need to quarantine live sand.

To quarantine the live rock, simply set up a separate, cycled, quarantine tank, and add normal fish food.

Check on the tank periodically; if you see that the food looks like something has been snacking on it, something probably has. It is then up to you to determine whether it is a fireworm, bristle worm, or something else entirely.

This will also help you keep better track of the smaller invertebrates in your tank. Hermit crabs and other such creatures also hitchhike in, and while most are harmless, there are a few other invertebrates that can cause issues later on.

Quarantining everything that comes into the tank is the only way to ensure that you are only adding what you want to add.

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