Bristleworms in Detail

Bristle Fire Worm

Bristleworms (also known as bristle worms) are segmented worms with bristly tufts on each segment. They may grow to be extremely huge in a tank, up to 24 inches long, although most are between one and six inches long. They prefer to stay under or beneath living rock or in the tank substrate at night. Unless you seek for bristleworms at night with a flashlight or expose them by moving a rock or shifting the substrate, you may never see one in your tank.

What Is a Bristleworm?

Bristleworms are members of the annelid family, and there are over 10,000 different species. They have segmented bodies with bristle-like protrusions called chaetae down their sides and are mostly found in the ocean (though rarely fresh water).

Identifying Bristleworms

If you believe you have bristleworms, the first step is to determine which variety you have. Some are good, while others may overrun your tank and create discomfort and other issues for your tank's residents if left alone. They reproduce quickly, and some are carnivorous, so they may need to emerge.


Do not touch bristleworms with bare hands. Their bristles are very thin and will embed in your skin, causing a severe itch.

Beneficial Bristleworms

Bristleworms may appear unattractive and creepy, yet most are beneficial to your aquarium provided they are not harmful. They eat things in your tank that would otherwise degrade and create ammonia, increasing the load that your biological filter must handle. In a saltwater tank, bristleworms are mostly scavengers, eating uneaten food, debris, and carrion. When they see a bristleworm chowing down on a cadaver in their aquarium, some people assume it has killed a fish. However, in most cases, the fish was already dead or dying before the bristleworm decided to consume it. Bristleworms that sting, such as fireworms, are the exception. At night, while the fish is resting in a crack or fissure of living rock, fireworms have been known to bite perfectly healthy fish (typically little ones).

Getting Rid of Bristleworms

In a reef tank with a lot of live rock, getting rid of bristleworms may be tough and time-consuming. Natural predators of bristleworms exist and can be effective in a tank. Among them are:

  • Wrasse of the Halichoeres family
  • (Gomphosus varius)
  • Maori Wrasse (Cheilinus oxycephalus)
  • Sunset Wrasse (Thalassoma lutescens)
  • (Stenopus hispidus)
  • Arrow Crab (Stenorhynchus setrcornis

While this is a popular alternative, care is urged. The nasty worms will be eaten by an introduced predator, but species like these will also devour desirable invertebrates and crustaceans. Once the bristleworms have been devoured, you'll need to deal with the new predators in your tank to keep the desired invertebrates alive.

If your live rock has bristleworms caught in cracks and crevices, just taking each piece of rock from the tank and immersing it in a bucket of dechlorinated freshwater for a few seconds will generally result in the worms flowing out of the rock and into the bucket's bottom.

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