They’re creepy, they’re crawly, and they kind of look like an underwater centipede. They’re Bristle Worms!

These weird little critters are segmented worms (similar in one sense, to earthworms) that are a part of the Polychaete family.

They love the dark. They’re nocturnal. And they love hitchhiking into aquariums on live rocks and other decorations that come from pet stores and retailers.

The name of these guys literally means “hairy worm” in Latin, or at least “many hairs” and, well, they look like the name fits them really well.

Let’s ask a few questions like, “Are bristle worms bad?” and “What’s the difference bristle worm vs fireworms?”

Let’s take a look at these critters and learn as much as we can so we know what to do – or not – with them when we find them in our aquariums.

bristle worms

What Is a Bristle Worm?

First off, it’s important to know what these critters are and where they come from to better understand what needs to be done with them when you find them in your aquariums.

There are about 8,000 species of bristle worms all over the world. About 168 of them are freshwater critters, while the rest prefer brackish or marine water.

They come in a ton of different sizes, too, from itsy bitsy, microscopic things up to 8-inch long guys that you just can’t miss.

The colors for them varies as well, from iridescent and even luminescent to very bland in coloring and everything in between.

The worms are like little cylinders in shape, and though they vary in looks from species to species and family to family, they are all covered in those weird little spines or “hairs” that earn them their name.

There are two basic types, too: Errant and sedentary.

Sedentary Bristle Worms

These guys are more burrowers and don’t really move around much. They like living in the substrate or in tubes and holes wherever they can find them.

Errant Bristle Worms

Errant worms use their parapodia to move around, so you’ll see them swimming and crawling around your fish tank with some fervor at night. Fireworms are an errant species.

What’s the Difference Between a Bristle Worm and a Fireworm?

And speaking of fireworms, you should understand the difference between them and bristle worms – or at least what different there is.

Fireworms are, simply put, a type of bristle worm. Bristle worms is the overarching species of animal, and fireworms are one of the subspecies or “breeds” of bristle worms.

Fireworms are usually viewed as pests in your saltwater reef tank. They are painful (thus the name) and usually unappreciated as residents.

Some other subspecies of bristle worms, however, are actually viewed as beneficial in many marine aquariums. This is a large part of why you do want to know the differences and values. We’ll go into more detail on identification below.

A Brief Overview of Bristle Worms

Common NameBristle Worms, Polychaete Worm, Polychaeta worm

What Do Bristle Worms Eat?

Alright. Now that you have a basic idea of what these critters are, lets take a look at their diet.

Bristle worms in general are scavengers and eat almost anything that they can get their little mouths on. They eat dead fish (a particular favorite dinner treat), but they are not fish killers in general.

They’re just scavenging, since this is, after all, what they do.

They also eat leaves and algae. In fact, they are particularly appreciate for their eating of algae. And sometimes people will intentionally invite them into their aquariums to help keep down the algae in the reef aquariums.

What Should You Feed Your Bristle Worms?

Since bristle worms are scavengers, you don’t need to feed them. They have plenty of algae, dead animal cells, feces, leaves, or anything else they feel like munching already at their disposal.

They will eat fish food, as well, that falls to the bottom of the tank, which is also helpful to avoid overfeeding of your fish.

Basically, these guys are a maintenance crew for your aquarium – if you have the right species.

Are Bristle Worms Good or Bad?

As mentioned above, there are both beneficial bristle worms and not so beneficial bristle worms. There are some that will help you clean up messes, prevent overfeeding, and devour your algae. Others, however, cause more issues than they solve.

Some species of bristle worms in reef tank situations are good. Especially if you have a problem with algae. These salt water bristle worms love to snack on algae, dead plants, fish waste, etc., which makes it a little easier for some beginners to care for a marine tank.

Bad bristle worms are those referred to as Fireworms, though not all of them are bad. Some are just harmless. The bad ones, however, are those who attack the plants and creatures you keep in your aquarium, such as corals.

The bearded fireworm loves to snack on corals, for example, so they’re definitely not your friend.

How Do You Tell the Difference Between Good and Bad Bristle Worms?

When you find a bristle worm aquarium situation, you need to learn quickly whether or not the worms are good or bad. There are more than 120 confirmed species of fireworms, though, so it might be a bit difficult. There are some common characteristics, however, that may help.

These guys tend to have more pronounced bristles with bright red and orange shades on their bodies. They’re also larger around than most other species of bristle worms.

They’re also more aggressive and generally more active than other species of bristle worms, so you’re actually more likely to see them than others. If one emerges during feeding times with lights on, that’s almost a dead giveaway that it’s a fireworm popping out to steal a snack.

Several Types of Most Common Bristle Worms

There are literally thousands of these worms around, so providing bristle worm pictures of them all would be impossible in a short online article. But there are a few distinct saltwater bristle worm types and freshwater bristle worm types that might appear most commonly in your home tank.

The Common Bristle Worms (Polychaete Linopherus)

This saltwater bristle worm is one of the good guys when it comes to your marine tank. They’re generally hitchhikers that come into your marine tank via live rock.

They’re a detritivore (meaning they eat detritus as their main diet) and aren’t a threat to your fish, they help clean your saltwater aquarium, and they do not go after your corals and fish.

They tend to be on the thinner side and a bit pinkish in color.

The Bearded Fireworms (Hermodice carunculata)

Hermodice carunculata (Bearded_Fireworm)
By Nhobgood (talk) Nick Hobgood – Own work, CC BY-SA 3.0

All right. These are the bad guys. They typically grow up to 6-inches long, though they can get up to 12-inches long. They have short tufts of white and red bristles on their colorful bodies, which could be gray, red, yellow, or green.

Red-Tipped Fireworms (Chloeia viridis)

This Fire bristle worm is another nasty guy with two stripes down the center of their backs. There’s a series of white spots creating the stripes over a light red to brown body with heavy white and red bristles covering them over. They’re less common than bearded fireworms, but just as nasty.

Bobbit Worms (Eunice aphroditois)

Eunice aphroditois
By Jenny – Flickr: “Aliens” movie star!, CC BY 2.0

This bristle worm typically gets up to nearly nine feet in length. Yes, these guys are huge. They do not live on ARC Live Rock, thankfully, so they won’t hitchhike their way in like that.

They have a large, retractable jaw with two pairs of scissor-like serrated plates over each other. They also have prominent beaded and banded antennae-like extensions on their heads.

These guys are also nasty and harmful to your wanted aquarium pets. So, if you spot them, remove them quickly to save your stock.

Should You Keep Bristle Worms In Your Aquarium?

There are definitely some good marine bristle worms. They’re an incredible cleanup crew that scavenges away and eat up dead, rotting things, be they old food, fish waste, plants gone bad, or, in unfortunate events, dead fish.

If they help clean the tank, they’re a good critter to keep around, unless they’re one of the nasty fireworms.

So, to put it more plainly: Keep the common bristle worms and ditch the fireworms.

Can You Have Too Many Bristle Worms?

In one sense, you can’t have too many good bristle worms. It’s more the fact that you have a ton that is the problem. If there are loads of these guys hanging out and thriving in your aquariums, it means there’s an abundance of food.

This means there’s too much food waste, fish waste, dead animals, or other things allowing these worms to scavenge and overpopulate.

Reasons You Might Not Want to Keep Bristle Worms in Your Aquarium

The good bristle worms aren’t really of much concern, unless they’re way too plentiful (which, as noted above, is more an issue with the aquarium than the worms themselves).

But fireworms are extremely dangerous to your fish, corals, plants, and even yourself, if you reach in and happen to come in contact with their venomous spines.

They won’t kill you by any stretch, but they’re sure as heck sting if they get you.

As to your plants, corals, fish, et cetera, fireworms will try to eat them. So, basically, if you want to keep your fish and corals happy and healthy, you want to get rid of fireworms.

How Do Bristle Worms Get in Your Tank If You Don’t Add Them?

Generally speaking, bristle worms in live rock is the basic way these guys get into your tank.

Your local pet store, retailer, or online shop may do their best to inspect live rock before they sell it, but there’s always the possibility that they missed some fireworms or common bristle worms somewhere along the way.

Do You Need to Remove Them If They Get In?

If you have fireworms in the mix, you do need to remove them. If you have common bristle worms, it’s really your preference on whether or not to chuck them out or not.

Common bristle worms will help you clean the tank. Fireworms will try to eat your fish. It’s kind of as simple as that.

How to Get Rid of Bristle Worms

If you do decide to rid your aquarium of bristle worms, there are three primary ways to do so.

Bristle Worms Traps

The first method for removing bristle worms if through the use of bristle worms traps. Some of the most effective traps are the ones that provide a one-way in and zero-ways out approach.

You can buy them at a store or you can find some DIY bristle worm traps online.

Natural Predators

Of course, if you’d prefer a more natural way to remove bristle worms, they do have some natural predators that you might appreciate having in your aquarium anyway. Just a few options include of what eats bristle worms:

  • Wrasse
  • Maori Wrasse
  • Bird Wrasse
  • Dottyback
  • Arrow Crab
  • Sunset Wrasse
  • Coral Banded Shrimp
  • Hawkfishes
  • Six Line Wrasse
  • Some Pufferfish – this is hit and miss, though
  • Some Butterflyfish – these are also hit and miss

Other Methods Of Removal

Finally, you can actually remove these little guys by hand. If you happen to see them in the tank, you can grab them with a pair of tweezers, one by one, and evict them from the water.

If you have small quantities of them hanging out, this is probably the easiest and most efficient – and cheapest – way to boot them. If you’re dealing with fireworms, remember to wear gloves to avoid their stinging hairs.

You can also remove sections of rock and sediment in which the fireworms have obviously been living. Put them into fresh, de-chlorinated water.

This will provoke the worms to come out of the crevices in the rocks. But this can also do harm to the good things living in your live rocks, so only do this if you’re desperate.

Preventing Bristle Worms From Getting In

Of course, the best way to “get rid of” bristle worms is actually through prevention of them in the first place. Every time you purchase a new live rock to put into your aquarium, double and triple-check them.

You can do this by having a control tank for the new rocks. It will keep the rocks live without killing the good critters, bacteria, et cetera living in them, but will reveal the bristle worms as they exit the rocks in search of food.

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