Should You Keep Bristle Worms In Your Aquarium?

These little worms have found their way into most, if not every saltwater aquarium. It is likely that you already have or will run into these creatures during your time as an aquarist.

But what exactly are bristle worms, how did they get here and should they be in your fish tank?

The answers to these questions are more complicated than people may think.

In this article we will talk you through everything you need to know about these worms, so you can decide for yourself if they should be in your aquarium.

Bristle Worm Overview

Bristle Worm
The Bearded Fireworm

Bristleworms, Bristle worms, or Polychaeta’s are a class of annelid worm (segmented worm) which are usually marine species. For any gardeners out there, think earthworms, but in the sea.

All worms in the class Polychaeta are known commonly as bristle worms.

They are made up of segments; each body segment has a pair of fleshy leg-like parts called parapodia.

Each segment also has a bunch of hair-like bristles called chaetae which are made of chitin.

They have been found all over the world, from some of the coldest regions to the hottest thermal vents. Some live planktonic lifestyles (meaning they’re unable to swim against the current), while others live in the deepest depths in the ocean.

One of these worms was found in The Challenger Deep; the deepest known part of the world’s oceans. This is just another example of how widespread these organisms are.

What Is A Bristle Worm?

There are over 8,000 species of bristle worms across the world. Only around 168, less than 2%, are freshwater, the rest are marine or brackish species.

These worms can be range in size, from tiny microscopic species, to others that exceed 50ft. However, most aquarium varieties are around 3-8 inches. The colors can also vary depending on the specific species. Some are even iridescent and luminescent.

They are cylindrical in shape, and their characteristics vary from family to family.

Bristle worms can be sectioned into two orders: sedentary and errant. Errant worms use their parapodia to move around, you’ll see them swimming and crawling around in the tank.

Sedentary species are either burrowers or live in tubes and don’t move around as easily.

One of the errant worms that is the notorious and not welcomed in most aquariums is the fireworm. The reason for this is because their bristles can break off in the skin of anyone passing by and cause intense pain.

It’s important to understand that there are thousands of species – some good and some not so good!

Should You Keep Bristle Worms In Your Aquarium?

Bristle Worm on Coral

In the wild, as well as your tank, these worms are incredible cleaners. They are scavengers and will eat any dead or rotting thing in your tank. This includes leftover food and dead animals.

They are also able to move through rocks and crevices and get into places other organisms cannot. They make great additions to your tanks cleaning crew.

Any organism that helps you clean the tank without causing your tank problems is a bonus.

Because these organisms enter the tank typically in live rock, it’s likely you will not have to pay for these little cleaners.

The good species can be just as effective at cleaning as snails or even some starfish.

Reasons Not To Keep Bristle Worms In Your Aquarium

The Bearded Fireworm
The Bearded Fireworm

Some bristle worms from the family Amphinomidae have hollow bristles which contain toxins than cause a burning sensation. As a result, these worms are known as fireworms.

Fireworms are most aquarist’s worst nightmare. They are the worst type of bristle worm to have in your tank. Fortunately, they aren’t as common as other species, but they can still hitch hike their way into your tank.

While most worms in your tank are detritivores (feeding on mostly detritus), some are carnivores. This means they will attack fish, usually as they sleep. Recently they were found to actually contain a venomous cocktail which explains the burning and pain that comes with contact.

These species pose a clear threat to your tank and should be removed immediately.

They are easily identified as they tend to grow much larger and have more defined color. If you see one that is very colorful with well-defined chaetae, then you might have a fireworm in your tank.

How To Tell The Difference Between Good And Bad Bristle Worms

There are around 120 confirmed species of fireworms, so it’s impossible to list them all. They have much more pronounced bristles, which often have a reddish color to their base. The main fireworm which gives bristle worms such a bad reputation is the bearded fireworm. This worm is a carnivore and will attack your fish and corals.

Here are a couple of pictures and videos to help you distinguish between the good and the bad. Keep in mind though, that with over 8,000 species, it’s very likely that yours will look slightly different.

The Common Bristle Worm (Polychaete)

Good Bristle Worm
A Common Bristle Worm

These are the good guys!

They normally hitchhike their way into your tank. They’re a detritivore and don’t pose a risk to your fish – they are great at keeping your tank clean. These worms tend to be thinner than fireworms, their bristles aren’t as pronounced and they are usually a pinkish color.

The Bearded Fireworm (Hermodice carunculata)

This species is from the Amphinomidae family and typically grows up to 6 inches but can reach lengths of 12 inches. They have short tufts of white and red bristles and various colored bodies including green, yellow, red or grey.

How To Remove Bristle Worms From Aquariums

Natural Predators

The good thing about these worms is there are plenty of natural predators that will eat them for you. Consider including some of the following creatures in your tank:

  • Arrow Crab
  • Sunset Wrasse
  • Dottyback
  • Maori Wrasse
  • Wrasse
  • Coral Banded Shrimp
  • Bird Wrasse

Some puffer fish and butterflyfish will also eat them. A lot of these species are also reef safe and are beautiful additions to your tank.

Many people do forget how important it is to add natural predators. They are one of the safest ways to control populations of other organisms.

Studies have been done on shrimp to show how much of an impact they really have in keeping certain unwanted populations down.

Bristle Worm Traps

If you are looking for a way to get rid of them without adding other fish, then traps are the next best thing. Some of the most effective traps are ones that use the one way in and no way-out approach.

You can go out and buy one or you can also easily make one yourself.

To make one, take a plastic bottle and cut it horizontally at the neck. Then flip the part you’ve just cut off (where you drink from) and glue it to the top of the bottle. This will create a funnel like shape at the top of your bottle.

Place bate in the bottom and bury the bottle upright in sand.

This will entice the worms into the trap, and when they fall into it, they will not be able to climb the sides of the bottle.

Other Methods

Some other ways of getting rid of these critters include removing them by hand. If you see them in your tank you can easily grab them with a pair of tweezers one by one. This is a good way to get rid of small quantities of them.

You can also take out sections of rock or sediment and put them in fresh, de-chlorinated water. This will make the worms come out of the rocks. Doing this can also harm other things living on your rock so use this as a last-ditch effort.

In general, the best way is prevention. Keep an eye on the rocks that you are putting into your tank every time. Make sure that nothing foreign is entering your tank.

You can easily achieve this by having a control tank that is just for new rock. This keeps the rock alive but lets you monitor what might be living on or in the rock.

Of course, this takes extra time and is a fairly slow process.

FAQs About Bristle Worms

Bristle Worm Close Up

Can You Touch A Bristle Worm?

Some are dangerous to touch, and others aren’t. To stay on the safe side, if you’re going to handle them use gloves. The bristles on the side of these worms can break off and cause skin irritation.

In severe cases it can cause nausea and dizziness.

Touching these worms usually happens by accident as you move rocks or sand around in your tank. Other than irritation you don’t have to worry too much about encountering these worms.

Bristle Worms vs Fireworms: What’s The Difference?

All fireworms are bristle worms but not all bristle worms are fireworms.

Their size is a good way to tell the difference as bristle worms are normally smaller.

The other difference is their defense mechanisms.

Should You Remove Bristle Worms From Your Aquarium?

Most of the time these worms will do your tank no harm, the most important thing is making sure you can identify which species you have.

This is often the hard part as seeing them is a challenge. They are mostly nocturnal and sleep for most of the day. Unless you have a large fireworm that is attacking your fish you really shouldn’t have a problem with a few of these in your tank.

Bristle Worm

What Do Bristle Worms Eat?

There are plenty of ways to feed your worms, but overfeeding is always something to avoid.

As said above, these worms are mostly scavengers. They will seek out anything that hits the bottom of your tanks.

This does lead a lot of people to see these worms on dead fish, thinking they have killed the fish. Whereas it is more likely that the fish died or was almost dead when the worms found their way to them.

In addition to dead fish they will eat algae and leaves.

Some species of bristle worms are sedentary, such as the Christmas tree worm, and have special appendages that they use to catch food as it floats by.

Summary

At first bristle worms can sound like a pretty serious threat to your tank.

But really these worms are just doing what they have to in order to survive. For the most part they are amazing at keeping your tank clean.

This means that keeping them in your tank is totally fine, unless they are fireworms.

Have you ever found these in your aquarium? We would love to hear about it in the comments section below!

Robert Woods Portrait
Robert Woods is the creator of FishKeeping World, a third generation fish keeper and a graduate in animal welfare and behavior. He is also a proud member of the Association of Zoos and Aquariums, the Marine Aquarium Societies of North America and the Nature Conservancy.

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