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All About Bristle Worms

Here’s what you should know about bristle worms in aquariums.

Bristle Fire Worm

Borut Furlan/Getty Images

The bristle worm is a segmented aquatic worm with bristly tufts extending from each segment. These worms can grow very large—up to 24 inches in a tank—but most are between 1 and 6 inches long. They are nocturnal and tend to stay in or under a live rock or in substrate.

You may never see a bristle worm in your tank unless you look for them at night with a flashlight or expose them by moving a rock or displacing the substrate. Nevertheless, it’s important to know the role they play in your aquarium, the benefits and drawbacks of having them in your tank, and how to safely remove them if necessary. Read on to learn everything you need to know about bristle worms.

What Is a Bristle Worm?

Members of the annelid family, the term bristle worm encompasses more than 10,000 species. Generally found in the ocean (but also occasionally in fresh water), they're characterized by segmented bodies with bristle-like protrusions—called chaetae—along their sides.

What Causes Bristle Worms?

When you purchase things like coral, live rock, or substrate to add to your aquarium, there might be bristle worms hiding in them. This results in you introducing these animals to your tank. 

Once in your tank, bristle worms can reproduce quickly if you don’t keep the tank as clean as possible by removing debris and ensuring you don’t overfeed your fish.

Identifying Bristle Worms

If you suspect you have bristle worms, the first thing to do is positively identify what type they are. Some types are beneficial, but those that are not can, if left alone, overrun your tank and cause irritation and other problems for your tank inhabitants. They multiply rapidly, and some are carnivorous, so they may need to come out.

The common bristle worm can be useful in your tank. However, the harmful bristle worms that you want to keep out of your aquarium include:

  • Bearded Fireworm
  • Bobbit Worm
  • Red-Tipped Fireworm

Fireworms are a type of bristle worm. They have poisonous bristles, their body is thicker, and they are more colorful (e.g., red and white), with more obvious bristles. Bristle worms will typically be thinner and colored gray or pink.

Warning

Do not touch bristle worms with bare hands. Their bristles are very thin and will embed in your skin, causing a severe itch. If a bristle worm stings you, use tape or tweezers to remove the bristles carefully. Cleanse the area, apply some rubbing alcohol or vinegar, and use corticosteroid cream if necessary. If the area gets infected, contact your doctor.  

Are There Benefits to Bristle Worms?

Bristle worms may look ugly and a little creepy, but most are actually good for your tank—if they are not the poisonous type. They consume materials in your tank that would otherwise decompose and produce ammonia, adding to the load that must be processed by your biological filter. Bristle worms primarily are scavengers and consume uneaten food, detritus, and carrion in a saltwater aquarium.

Do Bristle Worms Harm Fish?

Some people believe that a bristle worm in their tank has killed a fish when they find the bristle worm chowing down on a carcass. But in most cases, the fish was already dead or near death when the bristle worm decided to make a meal of it.

The stinging types of bristle worms, such as fireworms, are an exception. Fireworms have been known to attack perfectly healthy fish (usually small ones) at night when the fish are sleeping in a crack or crevice of live rock.

Getting Rid of Bristle Worms

Getting rid of bristle worms in a reef tank with a lot of live rock can be difficult and time-consuming. There are natural predators of bristle worms that can work quite well in a tank. These include:

  • Dottyback
  • Wrasse of the Halichoeres family
  • Bird Wrasse (Gomphosus varius)
  • Maori Wrasse (Cheilinus oxycephalus)
  • Sunset Wrasse (Thalassoma lutescens)
  • Coral Banded Shrimp (Stenopus hispidus)
  • Arrow Crab (Stenorhynchus setrcornis
illustration of predators that feed on bristleworms

The Spruce

While this option is very popular, caution is advised. An introduced predator will eat the bad worms, but species such as these also will eat desirable inverts and crustaceans. Once the bristle worms have been consumed, the new predators in your tank will have to be dealt with in order to preserve the desirable invertebrates in your tank.

How to Physically Remove Bristle Worms

If you have bristle worms lodged in cracks and holes of your live rock, simply removing each piece of rock from the tank and dipping it in a bucket of dechlorinated fresh water for just a few seconds usually results in the worms pouring out of the rock and into the bottom of the bucket.

If the offending bristle worms are found underneath your live rock, they can usually be picked up with a pair of tweezers or tongs and disposed of.

FAQ
  • Are bristle worms harmful to humans?

    Bristle worms aren’t harmful but their bristles sting, so wear gloves for protection when working on your aquarium.

  • What happens if a bristle worm stings you?

    Touching the bristles on a bristle worm will cause stinging and pain. Swelling and redness can also occur. Remove the bristles from your skin and clean and treat the area to prevent infection.

  • Do bristle worms have a purpose?

    Bristle worms help clean up the environment, so they can be useful in an aquarium as long as they are not predatory.