What Are Fireworms and Why Are They a Problem in Your Reef Tank?

Maintaining a healthy reef aquarium involves constant vigilance, especially when it comes to unwanted hitchhikers. One such problematic intruder is the fireworm, a type of predatory polychaete worm that can pose a threat to your tank’s inhabitants.

What Are Fireworms?

Fireworms are a group of bristle worms. While many bristle worms are harmless detritivores, fireworms are opportunistic predators with venomous bristles capable of harming both tank inhabitants and the tank owner.

They often enter aquariums as hitchhikers on live rock, coral frags, or substrate and are particularly active at night.

Why Are Fireworms a Problem?

While they’re natural scavengers, fireworms in reef aquariums can cause real damage, including:

• Eating coral tissue (especially soft corals, LPS, and zoanthids)
• Killing small invertebrates (snails, shrimp, feather dusters)
• Attacking and feeding on injured or sleeping fish
• Rapid reproduction under the radar

In short, they can be predatory, destructive, and difficult to catch if not managed early.

What Are The Signs That You May Have Fireworms?

Fireworms are often nocturnal, so spotting them can be tricky. DNA testing will be able to detect them, but you can also Look out for:

• Missing polyps or bite marks on soft coral tissue
• Shrinking or disappearing zoas
• Empty snail shells or missing shrimp

How to Identify Fireworms

Fireworms are visually similar to harmless bristle worms, but with a few distinct differences:

• Thicker, flattened bodies with a reddish or orange hue
• Prominent white bristles along their sides (used for defense)
• More active and aggressive, particularly at night
• Typically found in or under live rock, moving quickly when disturbed

Use a red-spectrum flashlight at night for improved observation, as fireworms are nocturnal.

 

Fireworm Removal Methods

1. Manual Removal (Ideal for Light Infestations)

Tools Required:

• Long tweezers or tongs
• Protective gloves (nitrile or aquarium-safe)
• Collection container

Procedure:

• Observe the tank at night under a red flashlight
• Carefully extract visible fireworms using tweezers
• Dispose of the worm in a secure container
  

Note: Do not handle with bare hands, the bristles can cause a painful sting!

 

2. Use a Targeted Trap

DIY Fireworm Trap:

• Use a small bottle or container with entry holes plugged with cut straws. This will allow for easy entry but hard escape. Add bait (shrimp, scallop, or fish) in the bottle and close lid.
• Place in the tank after lights out
• Check and empty each morning

Commercial Traps:

• There are commercial fireworm/bristle worm traps available in aquarium shops or online. 
• You can also buy a 3D printed trap or print one yourself.

Repeat the process nightly until no more worms are observed or caught.

 

3. Biological Control (Optional and Species-Dependent)

Certain reef-safe species have been observed to prey on fireworms, including:

• Arrow crabs (Stenorhynchus seticornis)
• Dottybacks (Pseudochromis spp.)
• Wrasses: Six-line (Pseudocheilinus hexataenia) or wrasses in the Halichoeres genus.

Caution: These species may exhibit aggression or predation toward other invertebrates and small fish. Introduce only if appropriate for your system.

 

4. Live Rock Treatment (for Severe Infestations)

In severe cases, affected live rock may need to be removed and treated externally:

• Remove corals and valued invertebrates from the live rock (with gloved hands)
• Submerge in high-salinity saltwater (1.040–1.050) or RODI water for 30 seconds. 
• Worms will exit rapidly due to osmotic shock (might not remove worms deep within the rocks)
• Rinse the rock with normal seawater to dislodge any fireworms and reintroduce into the tank. 

This method can be labor-intensive but is effective at flushing hidden worms. it can also impact the bacteria on the rock, if you decide to treat using this method, monitor ammonia and nitrites.

 

5. Prevention and Long-Term Management

• Dip and quarantine all new live rock, coral frags, and macroalgae
• Avoid overfeeding and maintain good nutrient control
• Regularly inspect tank during nighttime hours
• Siphon detritus and maintain substrate cleanliness

 

Fireworms infestation are a serious but manageable pest in marine aquariums. With early detection and a combination of manual removal, trapping, and habitat management, most infestations can be resolved without chemical treatments or dismantling your system.