What Is a Bristle Worm? Should You Treat Them In Your Aquarium?

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

Some reef keepers suggest that they should be avoided at all costs, while others suggest that they may be beneficial to the health of a liquid salt facility.

So should they stay or should they go?

On this topic, we discuss the pros and cons of leaving bristle worms in your fish tank or aquarium.

  • Usual Nickname: Bristle Worm
  • Scientific nickname: polychaete
  • Size: typically 1 “- 6” (can rise up to two feet)
  • Diet: mainly algae, uneaten fish food, and waste.
  • Color: pink or gray

What is a bristle worm?

The term “bristle worm” refers to thousands of different worms, each with different behaviors and anatomy. They are a variety of segmented worms and generally feature bristles along their sides, many of which are toxic and poisonous.

This presents a major problem for both you and some of your inhabitants, as if you rub against a rock that hides a bristle worm, you will end up with these bristles on your hand or arm.

As you can imagine, this is a problem for you and the different inhabitants of your tank. However, most bristle worms are peaceful and generally not harmful, unless a fish encounters them or is overly curious.

In fact, fish usually survive on a couple of bristle worms. In extension, the bristle worms are not capable of shooting their bristles at the fish or of applying them aggressively; they just fall off before something touches them. Most of them are detritivores or omnivores, and they eat the things that nothing else in the container will eat.

They will take care of the food of different fish and invertebrates missed, carcasses, and they will reprocess the waste of different creatures. In this way, they can be useful in the tank, identical to detritus worms in fresh liquid containers.

Other than detritus worms, there are a few nasty types that you can encounter.

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

The fireworm is the most frequently encountered; Its bristles are much more powerful than other bristle worms, and it frequently feeds on invertebrates, corals, and small fish.

The Bobbit worm is probably the worst you can find. It hides under the sand and hits upwards in the period when fish or different creatures are up, and its jaws are capable of cutting a fish in two. If you’re not careful, it can cause little serious damage to your arm or hand.

Pros of treating a bristle worm in your fish tank or aquarium

As mentioned above, these worms will consume various varieties of decaying matter, which can be incredibly helpful.

Most of the time you won’t even notice that you have bristle worms, as they frequently come out at night to wash the container of anything the different inhabitants have missed.

If you remove one suddenly, you will start to see more decomposing matter than before, which can, in some cases, bring a nitrite spike and ammonia, which is terribly harmful.

While it will likely only result in additional daily or weekly maintenance for you, in addition to a feeding adjustment, it may be worth leaving the worm where it is.

There is a low chance that a harmless bristle worm will reproduce by feeding only on the leftover matter, so they are unlikely to invade your tank.

In extension, as mentioned above, they will feed on the carcasses of dead fish. As you know, a decomposing fish will quickly raise its ammonia to unsafe layers, and if it can’t find the body quickly properly, it can crash your tank.

In fact, only a bristle worm will be able to help you reduce the amount of ammonia, or indeed find the body.

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

Cons of bristle worms

While bristle worms can be beneficial in removing decomposing matter from your container, they pose little danger. As mentioned above, in fact peaceful ones can have toxic bristles.

Fortunately, they only cause mild irritation, plus it’s up to you whether or not treating that risk near is worth it.

Just by moving a few rocks, the painful bristles can end up on your skin. While this is not a common occurrence, as most peaceful bristle worms are well hidden in rocks, it is a possibility to consider.

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